LINY LAROCHE
9Ó.S
UL-RELATION ENTRE L’INSOMNIE CHRONIQUE ET LE FONCTIONNEMENT IMMUNITAIRE
Mémoire Présenté
à la Faculté des Études Supérieures de l’Université Laval
pour l’obtention
du grade de maître en psychologie (M.Ps.)
École de Psychologie
FACULTÉ DES SCIENCES SOCIALES UNIVERSITÉ LAVAL
DÉCEMBRE 1999
Québec, le 20 décembre 1999
OBJET : Mémoire de maîtrise présenté à la Faculté des Études Supérieures de ΓUniversité Laval par Liny Laroche intitulée : « Relation entre l’insomnie chronique primaire et le fonctionnement immunitaire ».
Madame, Monsieur,
Par la présente, les soussignés co-auteurs d’un article intitulé « Chronic Insomnia and
Immunity » faisant partie du mémoire de maîtrise présentée à la Laculté des Études Supérieures de l’Université Laval par Liny Laroche donnent leur autorisation pour l’insertion de cet article dans le mémoire et l’éventuel microfilmage de ce mémoire selon les règles de la Bibliothèque nationale du Canada.
En espérant le tout conforme, veuillez, Madame, Monsieur, accepter mes plus cordiales salutations.
Éü
3
Liny Laroche, candidate
Josée Savard, Ph.D.
/TUM
Résumé
L’objectif du présent mémoire est de comparer le fonctionnement immunitaire d’individus souffrant d’insomnie clinique à des individus considérés bons dormeurs. Le groupe « bons dormeurs » est composé de 19 adultes qui dorment habituellement entre 7 et 9 heures par nuit et ne rencontrent pas les critères diagnostiques de l’insomnie. Le groupe des « insomniaques » est composé de 18 adultes présentant un syndrome d’insomnie chronique primaire, tel qu’évalué par une entrevue semi-structurée et deux semaines d’auto-enregistrement du sommeil. Des échantillons sanguins ont été pris au moment de l’entrevue ainsi que lors de la deuxième nuit d’enregistrement polysomnographique afin d’évaluer la production d’IL-1-β , d’IL-2 et d’IFN-γ ainsi que le pourcentage des sous-populations de lymphocytes suivantes : a) T; b) T-auxiliaires; c) T-cytotoxiques; et d) cellules NK. Aucune différence significative n’est observée entre les groupes sur les variables démographiques et les variables reliées aux comportements de santé. Bien que certaines tendances soient observées, les paramètres immunitaires ne diffèrent pas significativement entre les deux groupes, à !’exception de la production d’IL-2 qui est plus élevée chez les participants insomniaques. Ces résultats suggèrent que les individus souffrant d’insomnie n’ont pas un fonctionnement immunitaire plus faible que des individus considérés bons dormeurs.
Avant-propos
OUF! C’est avec grand soulagement queje dépose ce mémoire à l’aube du deuxième millénaire...
D’abord, merci à toi Josée. Sans ton support je n’aurais pu réaliser cette recherche ni déposer mon mémoire à temps... Je sais bien que mon « changement de carrière » au cours de ma maîtrise m’a plutôt détournée des objectifs queje m’étais fixés avec toi au départ et que cela t’a apporté des déceptions... J’en suis sincèrement désolée. Merci aussi à vous M. Morin, pour votre compréhension et votre flexibilité.
J’ai eu la chance de travailler à l’intérieur de deux groupes de recherche où j’ai trouvé support moral et technique. Merci au labo du sommeil, particulièrement à Sébastien pour notre été au téléphone, ainsi qu’à Célyne, Ginette, Véronique, Marie-Ève, Daniel et Linda. Merci également au groupe de recherche en psycho-onco, particulèrement à Sébastien S., Mylène, Catherine, Lucie et Claudia.
Un projet multidisciplinaire comme celui-ci ne se fait pas sans la collaboration de plusieurs personnes. Je désire donc remercier pour leur participation à l’étude les techniciennes du labo du sommeil, les « infirmières » Paule et Christian ainsi que les techniciennes de
l’Interface Clinique, Marie-Anne et Nancy. Un merci spécial à Hans, mon mentor de la
psychologie de la santé, pour ses précieux conseils statistiques et son oreille toujours disponible! Je ne peux surtout pas oublier mes amis qui n’ont jamais cessé de m’écouter et de m’encourager même si je leur ai sûrement souvent cassé les pieds... Merci Mélanie, Hélène & Marc, Mireille, Valéry & Michel, Yannick (merci pour tes conseils de biochimiste!), Jean- Philippe, Thierry, Chantal et Andou ainsi que Kim et Geneviève.
Merci aussi à ma « gang de pré-méd », Philippe, Marie-Hélène, Caro et Julie, qui en plus de me supporter et de m’encourager ces derniers mois, m’ont permis de délaisser parfois la médecine au profit de mon mémoire.
Enfin, le dernier merci et non le moindre... Ma famille : Pauline, Vital, Jasmin, Joé et Nancy. Merci pour tout ce que vous avez pu faire pour me faciliter la tâche pendant ces deux dernières années (que ce soit pour un encouragement, un lunch, un lift ou une imprimante!). Merci particulièrement à mes parents qui, par leur exemple, m’ont appris à toujours persévérer...
TABLE DES MATTERES
RÉSUMÉ
AVANT-PROPOS iii
TABLE DES MATIÈRES iv
LISTE DES TABLEAUX vi
CHAPITRE 1 : INTRODUCTION 1
1.1 Introduction 2
1.2 L’insomnie : prevalence et définition 2
1.3 Impact du sommeil sur la santé 3
1.4 Psychoneuroimmunologie 4
1.5 Sommeil et fonctionnement immunitaire 5
1.6 Pertinence et objectif de l’étude
CHAPITRE 2 : RELATION ENTRE L’INSOMNIE CHRONIQUE ET LE FONCTIONNEMENT IMMUNITAIRE (ARTICLE)
10 2.1 Page-titre 12 2.2 Résumé 13 2.3 Front page 14 2.4 Abstract 15 2.5 Introduction 16 2.6 Method 19 2.6.1 Participants 19 2.6.2 Procedure 21 2.6.3 Measures 21
2.6.3.1 Subjective sleep assessment 21
2.6.3.2 Polysomnography 22
2.6.3.3 Psychological measures 23
2.6.3.4 Health practice 23
V
2.6.4 Statistical analyses 26
2.7 Results 27
2.7.1 Preliminary analyses 27
2.7.2 White blood cells counts 28
2.7.3 Cytokines 28
2.7.4 Immune parameters stability 29
2.8 Discussion 29
2.9 References 34
2.10 Tables 38
CHAPITRE 3 : CONCLUSION 44
3.1 Principaux résultats 44
3.2 Limites et forces de l’étude 44
3.3 Implications et recherches futures 45
RÉFÉRENCE (INTRODUCTION ET CONCLUSION) 47
INTRODUCTION Figure 1 ARTICLE Table 1 Table 2 Table 3
CHAPITRE I
1.1 Introduction
Ce chapitre vise à introduire la problématique à l’étude dans ce mémoire. La première section aborde la prévalence de l’insomnie dans la population générale ainsi que la définition clinique de l’insomnie. L’impact que le sommeil peut avoir sur la santé est ensuite décrit. Puis, le domaine de recherche de la psychoneuroimmunologie, le cadre théorique utilisé dans ce
mémoire, est expliqué. La relation entre le sommeil et le fonctionnement immunitaire est par la suite discutée en décrivant brièvement les études ayant été menées sur le sujet. Enfin ce chapitre se termine avec la présentation de l’objectif de cet étude.
1.2 L’insomnie : prévalence et définition
L’insomnie compte parmi les plaintes les plus fréquentes en pratique clinique (Morin, 1991). Des études épidémiologiques suggèrent que près du tiers de la population souffrent d’insomnie de façon occasionnelle, alors que 9 à 15% souffrent d’insomnie chronique (Ford & Kamerow, 1989; Gallup Organization, 1991; Mellinger, Balter & Uhlenhuth, 1985).
Il n’existe pas de définition unique de l’insomnie. Elle peut d’abord se présenter sous plusieurs formes (i.e., insomnie initiale, de maintien et/ou tardive). On distingue également l’insomnie chronique (i.e., durée de plus de 6 mois) de l’insomnie subaiguë (i.e., durée entre 1 et 6 mois) et situationnelle (i.e., durée de moins de 1 mois). Selon les critères combinés de
1’ «International Classification of Sleep Disorders » (ICSD; American Sleep Disorders
Association (ASDA), 1990) et de la quatrième édition du « Diagnostic and Statistical Manual for Mental Disorders » (DSM-IV; American Psychiatrie Association [APA], 1994) le syndrome d’insomnie se définit par : a) un temps nécessaire pour s’endormir (latence du sommeil) ou un temps d’éveil après s’être endormi supérieur à 30 minutes par nuit; b) une efficacité du sommeil (ratio de la durée totale du sommeil sur le temps passé au lit) inférieure à 85%; c) une fréquence
Introduction 3
de ces difficultés d’au moins 3 nuits par semaine; et d) elles sont associées à une détérioration significative du fonctionnement social et occupationnel pendant le jour ou à une détresse marquée. Il convient également de définir l’insomnie primaire, qui n’est pas liée ou causée par un autre trouble du sommeil ou un trouble psychopathologique et qui n’est pas due aux effets physiologiques directs d’une substance ou d’une condition médicale générale (APA, 1994). 1.3 Impact du sommeil sur la santé
Il y a des milliers d’années, Hippocrate croyait déjà que le sommeil avait un impact important sur la santé. Encore aujourd’hui, cette idée est véhiculée tant par les médecins que la population générale malgré le fait qu’il n’existe pas encore de preuves empiriques solides démontrant directement la valeur préventive ou récupératrice du sommeil sur la santé (Krueger & Toth, 1994). Certaines études suggèrent néanmoins que la qualité et la quantité du sommeil auraient un impact sur la santé. En effet, plusieurs études révèlent que les patient souffrant d’insomnie consultent plus fréquemment les ressources médicales (Ford & Kamerow, 1989) et sont hospitalisés plus fréquemment que les bons dormeurs (Johnson & Spinweber, 1983). Sur le plan clinique, les individus qui soufrent d’insomnie chronique se disent aussi plus vulnérables à contracter une grippe, une diarrhée ou une autre infection (Morin, 1993). Par ailleurs, deux études épidémiologiques prospectives révèlent que les individus qui rapportaient dormir moins de 4 (Kripke, Simons, Garfinkel & Hammond, 1979) ou de 6 (Wingard & Berkman, 1983) heures par nuit présentaient un risque de mortalité (causes confondues) au moins 1.5 fois plus élevé que les individus qui dormaient de 7 à 8 heures par nuit. Bien que ces données suggèrent que la qualité et la quantité puissent affecter la santé, il existe peu d’évidence empirique directe pour supporter ce lien.
1.4 Psychoneuroimmunologie
La psychoneuroimmunologie est un domaine de recherche relativement récent qui procure un cadre théorique permettant d’expliquer un tel lien entre la qualité du sommeil et la santé. Plus précisément, la théorie psychoneuroimmunologique s’intéresse aux interrelations entre les facteurs psychologiques, neuro-endocriniens et immunitaires (voir figure 1). Elle
postule, par exemple, que les facteurs psychologiques ont un impact sur l’immunocompétence, et donc sur la capacité du système immunitaire à combattre les pathogènes, ce qui aurait à son tour un impact néfaste sur la santé (pour une brève définition des composantes principales du système immunitaire voir Annexe A). Ainsi, selon cette perspective, des états émotionnels comme la dépression et le stress auraient un impact sur l’immunité des individus et, par conséquent, sur le développement ou la progression des maladies physiques. De la même façon, des détériorations au plan du fonctionnement immunitaire pourraient être considérées comme un facteur médiateur de l’impact du sommeil sur la santé physique (Krueger & Toth, 1994).
Figure 1
FACTEURS PSYCHOLOGIQUES (comportements, émotions et cognitions)
FONCTIONNEMENT IMMUNITAIRE <
FONCTIONNEMENT NEURO-ENDOCRINIEN
Introduction 5
1.5 Sommeil et fonctionnement immunitaire
Bien que le lien entre le sommeil et la santé ne soit pas encore prouvé, différents champs d’études suggèrent l’existence d’une relation bidirectionnelle entre le sommeil et le
fonctionnement immunitaire. Les chercheurs se sont d’abord intéressés à l’impact que le fonctionnement immunitaire peut avoir sur le sommeil. Cette hypothèse a été testée dans le contexte de la régulation du sommeil ainsi que dans le contexte des infections bactériennes et virales. Ce n’est que plus récemment que les chercheurs ont aussi commencé à s’intéresser à la relation inverse, c’est-à-dire, à l’impact que le sommeil peut avoir sur le fonctionnement immunitaire. Cette hypothèse a été testée dans le contexte de la privation totale ou partielle de sommeil chez les animaux et les humains ainsi que dans le contexte de la dépression.
1.5.1 La régulation du sommeil : Bien que l’idée d’une régulation hormonale du sommeil soit très ancienne, les expérimentations s’adressant à ce problème n’ont débuté qu’au tournant du vingtième siècle. Legendre et Pieron (1913) et Ishimori (1909) postulaient
l’existence d’une hypnotoxine dans le fluide cérébro-spinal (FCS) d’animaux privés de sommeil puisque l’infusion de ce FCS dans un animal normal induisait un sommeil long et profond. Il y a près de vingt-cinq ans, ces recherches ont été reprises par Pappenheimer et ses collègues (1975) qui isolèrent du FCS d’animaux privés de sommeil une substance spécifique promouvant le sommeil, appelé facteur S. Cette substance a été identifiée comme une muramyl peptide (MP), qu’on peut retrouver sur la paroi cellulaire de certaines bactéries. Cependant, l’effet
somnogénique de la MP s’observait seulement après un délai d’une heure suivant son injection, ce qui suggérait que l’effet dépendait plutôt de la synthèse d’un autre composé.
L’interleukine-1 (IL-1), une cytokine, serait ce composé. En effet, cette découverte a mené au premier rapport de l’action somnogénique d’IL-1 (Krueger, Dinnarello, & Chedid,
1983) puisque la MP est connue pour induire la synthèse et la libération de cette cytokine. Le terme cytokine réfère à un groupe de protéines régulatrices qui sont des médiateurs clés dans plusieurs réponses immunitaires (Opp, Kapas & Toth, 1992). L’IL-l (plus spécifiquement IL-lß) est connue pour affecter directement et indirectement une variété de fonctions immunologiques, incluant la prolifération et la différenciation des lymphocytes T et B, la production de
l’Interleukine-2 (IL-2) et la stimulation des cellules « natural killer » (NK) (Dinarello, 1984). Outre l’IL-l, d’autres cytokines, telles que l’interféron-alpha (IFN-a), le facteur
nécrosant des tumeurs-alpha (TNF-a) et le facteur nécrosant des tumeurs-bêta (TNF-ß), ont par la suite été identifiées comme somnogéniques (Krueger, 1990). On retrouve d’ailleurs depuis une dizaine d’années une prolifération de la littérature scientifique sur la régulation du sommeil par les cytokines et certains neuromodulateurs reliés. Un type d’expérience effectué consiste à infuser dans les ventricules cérébraux latéraux d’animaux des cytokines humaines. Krueger, Walter, Dinarello, Wolff et Chedid (1984) ont observé une augmentation rapide (proportionnelle à la dose) du sommeil non paradoxal suite à l’infusion d’IL-1. Un autre type d’expérience effectué consiste à observer les variations des paramètres immunitaires en fonction des stades de sommeil mesurés à l’aide de 1 ’électroencéphalogramme (EEG). Par exemple, Moldofsky, Lue, Eisen, Keystone et Gorczynski (1986) ont observé que le début du sommeil non-paradoxal chez les humains coïncide avec une augmentation significative de la production d’IL-1 suivie d’une augmentation de la production d’IL-2 dans le plasma.
Infections bactériennes et virales : Un autre type d’étude consiste à observer l’effet des infections virales ou bactériennes sur le sommeil ainsi que la progression d’infections en
fonction du sommeil obtenu. Une tendance à passer plus de temps en sommeil non-paradoxal a été observée chez des lapins inoculés par le staphyloccus aureus comparativement aux animaux
Introduction 7
contrôles (Krueger & Toth, 1994; Toth & Krueger, 1987). Toth et Krueger (1988) ont également observé que parmi des lapins inoculés par le staphyloccus aureus, ceux qui ne présentaient pas davantage de sommeil non-paradoxal présentaient un état clinique plus morbide que les autres lapins infectés. Pour expliquer ces résultats, les auteurs ont proposé que les produits constituant les bactéries et les champignons, tels que la muramyl peptide, l’endotoxine et la polysaccaride, stimulent les réponses immunitaires, ce qui résulte en une libération d’immunomodulateurs qui induisent à leur tour des changements au niveau du sommeil. Cette hypothèse expliquerait la période de latence de 2 à 4 heures suivant l’inoculation avant !’augmentation du sommeil non- paradoxal. Une autre étude de ce genre démontre que des souris inoculées par le virus
d’influenza ne parviennent pas à combattre le virus lorsqu’elles sont privées de sommeil pendant l’inoculation comparativement aux souris n’ayant pas été privées de sommeil (Brown, Pang, Husband & King, 1989).
Quelques observations de ce type ont également été effectuées chez l’humain. Deux études ont révélé une augmentation de sommeil non-paradoxal pendant la seconde partie de la nuit chez les personnes séropositives au VIH (Norman, Chediac, Kiel & Cohn, 1990; Norman, Shaukat, Way, Cohn & Resnick, 1987). D’autre part, les personnes atteintes de cancer recevant une thérapie à l’IL-1 rapportent une somnolence excessive (Dinarello, 1991).
Privation de sommeil : L’impact de la privation partielle et totale de sommeil a été étudié dans plusieurs recherches sur les animaux et les humains. Concernant les études menées auprès d’animaux, il a été démontré qu’une privation totale de sommeil (PTS) (i.e. sans aucun sommeil) d’environ trois semaines suffit pour causer la mort chez la majorité des rats (pour une revue, voir Rechtschaffen, Bergmann, Everson, Kushida & Gilliland, 1989). Pendant plusieurs années, les chercheurs ne réussissaient pas à identifier le médiateur physiologique en cause. Il a
été récemment postulé que le taux élevé de létalité suite à la PTS prolongée est causé par une panne dans la défense de l’hôte qui permet aux pathogènes, que le système immunitaire contrôle normalement, de se propager dans le flux sanguin, déclenchant ainsi une série mortelle de réactions chimiques (Everson, 1993).
Dans les études portant sur l’impact de la PTS sur l’immunité chez l’humain, les auteurs utilisent généralement des périodes de privation de sommeil variant entre 48 et 70 heures. Plusieurs recherches de ce type ont été effectuées mais les résultats ne s’avèrent pas toujours constants. Néanmoins, les résultats les plus fréquemment observés suite à une PTS chez
l’humain sont : une augmentation de la réponse immunitaire non-spécifique (ex. : le nombre de phagocytes, le nombre de cellules NK et l’activité des cellules NK), une diminution de
l’immunité à médiation cellulaire (ex. : le décompte lymphocytaire) et aucun effet apparent sur l’immunité humorale (Dinges, Douglas, Hamerman, Zaugg & Kapoor, 1995). Everson (1993) a décrit la chaîne de réactions immunitaires typique après deux nuits de PTS. D’abord, le nombre de monocytes dans la circulation sanguine augmente. Par la suite, il y a une augmentation du nombre de cellules NK et de leur cytoxicité. La concentration d’interférons et d’interleukines augmente également à ce moment. Après une nuit de récupération, le fonctionnement
immunitaire revient à la normale, suggérant que la PTS sur une courte durée n’aurait pas d’impact significatif sur la santé.
Dans la vie courante, il est rare que les individus ayant des difficultés de sommeil ne dorment pas du tout dans une nuit. L’étude de la privation partielle de sommeil (PPS) offre donc l’avantage de représenter plus fidèlement la réalité clinique et les résultats peuvent ainsi mieux se généraliser à l’insomnie. L’effet de la perte de sommeil pendant seulement une partie de la nuit sur la réponse immunitaire demeure toutefois relativement inexploré. Seulement deux études ont
Introduction 9
été menées jusqu’à présent. Irwin et ses collaborateurs (1994) ont observé une réduction
significative de l’activité des cellules NK lorsque les participants étaient privés de sommeil entre 3h00 et 7h00 du matin. Une réduction de l’activité des cellules NK a également été observée suite à une privation de sommeil en début de nuit (entre 23h00 et 3h00) en plus d’une diminution du pourcentage de cellules NK, une diminution de la production d’IL-2 par stimulation des lymphocytes-T, ainsi qu’une réduction de l’activité des cellules tueuses induite par l’IL-2 (« lymphokines activated killer ») (Irwin et al., 1996).
Dépression et fonctionnement immunitaire : Plusieurs études démontrent une certaine immunosuppression chez les patients dépressifs (Herbert & Cohen, 1993; O’leary, 1990; Weisse,
1992). Il n’est cependant pas clair si 1 ’immunosuppression observée est une conséquence de la dépression comme telle ou de seulement certains symptômes qui y sont associés (Herbert & Cohen, 1993). En effet, Cover et Irwin (1994) ont observé que seuls deux symptômes de dépression, soit la baisse de l’activité motrice et l’insomnie initiale (évalués en utilisant le « Hamilton Depression Rating Scale » [HORS]) étaient significativement associés à la
cytotoxicité des cellules NK. De plus, il n’y avait pas d’association entre les autres sous-échelles du HORS, ou même la cote total au HDRS, et l’activité lytique des cellules NK.
Dans une autre étude, Irwin, Smith et Gillin (1992) ont utilisé des mesures
électroencéphalographiques du sommeil pour comparer des sujets dépressifs à un groupe
contrôle. Ils ont ainsi observé que la durée totale de sommeil, l’efficacité du sommeil et la durée du sommeil non-paradoxal présentaient une corrélation positive avec l’activité lytique des cellules NK, et ce indépendamment du niveau de dépression ou de la présence d’un trouble de l’humeur. Ces deux études suggèrent donc que l’insomnie et non la dépression serait responsable de l’immunosupression observée.
1.6 Pertinence et objectif de l’étude
En somme, plusieurs études semblent indiquer l’existence d’un lien bidirectionnel entre le sommeil et le fonctionnement immunitaire. Les études de privation de sommeil et les études sur le sommeil et le fonctionnement immunitaire des personnes dépressives sont particulièrement intéressantes pour l’étude de la relation entre l’insomnie et le fonctionnement immunitaire. Néanmoins, ces études comportent certaines lacunes, notamment, dans les deux études portant principalement sur la dépression, l’insomnie était considérée comme un symptôme plutôt qu’un syndrome et n’était donc pas évaluée selon les critères diagnostiques normalement utilisés, soit ceux du DSM-IV ou de l’ICSD. Par ailleurs, les études de la PTS et de la PP S sont des stresseurs de laboratoire à court terme, ce qui rend difficile la généralisation de ces résultats à l’insomnie. Il est possible de croire que l’insomnie, qui constitue un problème chronique de sommeil, serait encore plus susceptible d’avoir des conséquences significatives sur l’immunité et la santé. Pourtant, l’impact du syndrome d’insomnie chronique sur l’immunité n’a jamais été étudié directement.
Le présent projet a donc pour but d’évaluer la relation entre l’insomnie primaire
chronique et l’immunocompétence en comparant, sur le plan immunitaire, un groupe d’individus souffrant d’insomnie chronique primaire à un groupe d’individus considérés bons dormeurs évalués à l’aide de critères diagnostiques valides et rigoureux. L’hypothèse stipulée au départ était que les participants souffrant d’insomnie chronique (tel que diagnostiquée en utilisant les critères combinés de l’ICSD et du DSM-IV) manifesteront une immunocompétence
significativement plus faible que les participants bons dormeurs, et ce en contrôlant pour l’âge et les habitudes de santé pouvant avoir un impact potentiel sur l’immunité.
CHAPITRE II
Relation entre l’Insomnie chronique primaire et
le fonctionnement immunitaire
Liny Laroche, B.A., Josée Savard, PhD, et Charles M. Morin, PhD
École de psychologie et Centre de recherche sur le cancer Université Laval, Québec, Canada
Résumé
Plusieurs études ont documenté l’impact de la privation de sommeil sur le
fonctionnement immunitaire. Bien que les résultats de ces études soient plutôt consistants à démontrer un effet, la privation expérimentale de sommeil constitue un stresseur de laboratoire à court terme qui ne peut être généralisé à l’insomnie clinique. Cette étude compare, sur le plan immunitaire, des individus souffrant d’insomnie clinique à des individus considérés bons dormeurs. Le groupe « bons dormeurs » est composé de 19 adultes qui dorment habituellement entre 7 et 9 heures par nuit et ne rencontrent pas les critères diagnostiques de l’insomnie. Le groupe « insomnie » est composé de 18 adultes présentant un syndrome d’insomnie chronique primaire, tel qu’évalué par une entrevue semi-structurée et deux semaines d’auto-enregistrement du sommeil. Des échantillons sanguins ont été pris au moment de l’entrevue (Temps 1) ainsi qu’avant la seconde nuit d’enregistrement polysomnographique (Temps 2), incluant
l’énumération de : a) lymphocytes T (CD3); b) lymphocytes T-auxiliaires (CD4); c) cellules NK (CD16-CD56); et d) lymphocytes T-cytotoxiques (CD8). La production de cytokines (i.e., IL1- ß , IL-2 et IFN-γ) a également été évaluée. Aucune différence significative n’est observée entre les groupes sur les variables démographiques (i.e., âge, genre, éducation) et les variables reliées aux comportements de santé (i.e., consommation de cigarettes, alcool et caféine). Au Temps 2, la production d’IL-2 était significativement plus élevée chez les individus souffrant d’insomnie comparativement aux bon dormeurs. Aucun des autres paramètres immunitaires étaient
significativement différents entre les groupes, bien que certaines tendances soient observées chez les participants insomniaques à présenter un pourcentage moins élevé de lymphocytes T. Ces résultats préliminaires suggèrent que les individus souffrant d’insomnie n’ont pas un
Liny Laroche, B.A., Josée Savard, PhD, and Charles M. Morin, PhD
École de psychologie and Cancer Research Center Université Laval, Québec, Canada
Abstract
Several studies have documented the impact of experimental sleep deprivation on
immune functioning. Although the data from those studies are fairly consistent in demonstrating an effect, experimental sleep deprivation is a short-term laboratory stressor that may not
generalize to clinical insomnia. This study compares individuals with clinical insomnia to good sleepers on immunity. The “good sleepers” group was composed of 19 adults who habitually slept between 7 and 9 hours per night and did not meet criteria for an insomnia disorder. The “insomniacs” group was composed of 18 adults with a diagnosis of chronic and primary
insomnia, as assessed using a semi-structured interview and a 2-week sleep diary. Blood samples were taken at the interview (Time 1) and before the second night of polysomnographic
assessment (Time 2) for immune measures, including enumeration of: a) lymphocyte T (CD3); b) helper T (CD4) cells; c) NK (CD16-CD56) cells; and d) cytotoxic/suppressor T (CD8) cells. Cytokines (i.e., IT-Iß, IL-2, and IFN-γ) production was also evaluated. The results showed no significant difference between groups on demographics (i.e., age, gender, education) and health behavior variables (i.e., smoking, alcohol, and caffeine use). The IL-2 production was
significantly higher in insomniac patients than in good sleepers at Time 2. None of the other immune parameters were significantly different between groups, although there were trends for participants with insomnia to have lower percentage of lymphocyte T. These preliminary
INTRODUCTION
Insomnia is a prevalent condition affecting approximately 10% of the adult population on a chronic basis (1-3). Insomnia may involve trouble falling asleep (i.e., initial insomnia),
frequent or prolonged nocturnal awakenings (i.e., middle insomnia), or early morning awakening with an inability to return to sleep (i.e., late insomnia). It is commonly believed that sleep loss increases an individual’s vulnerability to diseases and, conversely, that sleep has a determinant role in illness recovery. Indeed, several studies have demonstrated that insomnia was associated with poorer health status compared to good sleepers (1, 4-6). Patients suffering from insomnia report poorer subjective health (7-9), seek medical care more frequently (1), and are hospitalized more often than good sleepers (10).
Although there is no direct empirical evidence to clearly demonstrate the preventive and recuperative value of sleep on health, it has been proposed that immune functioning acts as a mediator in the relationship between sleep and health (11). Specifically, sleep would be essential for optimal host defense functioning, whereas sleep loss would be associated with changes in some immune parameters, increasing the vulnerability to pathogens (12, 13). This hypothesis is indirectly supported by some evidence from epidemiological studies. For instance, an increased incidence of infections, an event associated with immunosuppression, was observed among participants experiencing disturbed sleep-wake rhythms (e.g. shift workers) (14, 15).
Furthermore, an association between mortality and sleep duration has been observed in longitudinal studies (16, 17). More specifically, sleeping less than 4 hours per night was associated with a 2.8 higher rate of mortality for men and a 1.5 higher rate for women in comparison with people sleeping from 7 to 8 hours (17).
Several animal studies supported the hypothesis that sleep loss increases the risk of infections through alterations in immune functioning. Sleep deprivation in rats produces
Chronic Insomnia and Immunity 17
septicemia and can even lead to mortality if prolonged over 3 weeks (18). This effect is commonly attributed to immune modulations. Brown (19) showed that mice immunized to influenza virus and then inoculated by the virus failed to clear the virus from their lungs when they were sleep deprived at the time of the inoculation.
The role of sleep disturbance in the modulation of immune functions in human has been tested mostly by examining the effect of total sleep deprivation (TSD; i.e., 48 to 72 hours without sleep) on several immune parameters. Despite some inconsistencies across studies, the findings suggest that total sleep deprivation increases non-specific responses (e.g., phagocyte and NK cell number and NK cell activity) and decreases cellular immune functioning (e.g., T-
lymphocytes, cytokines), with no effect on humoral immune function (e.g. B-lymphocytes) (20). Only three studies have documented the impact of partial sleep deprivation (PSD) on immune functioning. Irwin and his colleagues (21) observed a significant decrease in NK cell activity after an early-night PSD, as well as a reduction of NK cells number in the peripheral blood and a decrease of Interleukin-2 (IL-2) and induced lymphokine activated cell activity. A significant decrease of NK cell activity was also observed following a late-night PSD (22). Another study revealed no effect of a late-night PSD on circulating level of IL-2 of participants (23).
Although these data are fairly consistent in demonstrating an effect of sleep deprivation on immunity, experimental sleep deprivation may not generalize to sleep loss experienced by individuals suffering from clinical insomnia. Even partial sleep deprivation, the procedure that resembles most to naturalistic insomnia (because individuals with sleep difficulties usually sleep a portion of the night), remains a short-term laboratory stressor. Moreover, if situational or temporary sleep difficulties have an effect on immunity, one could reasonably hypothesized that chronic insomnia would have a stronger impact on immunity and health.
The limited data available on the relationship between insomnia and immunity have been obtained in the context of depression. In one study, electroencepalographic (EEC) measures of total sleep time and sleep continuity (i.e., sleep latency and sleep efficiency) were significantly associated with NK cell activity in both depressed patients and in control participants,
independently of severity of depression or presence of a mood disorder (24). Moreover, the severity of insomnia, as measured by the Hamilton Depression Rating Scale (HDRS), was significantly correlated with decreased NK cell activity in patients with major depression while there was no association between HDRS total score and NK cell activity. These data suggest that insomnia is a better predictor of immunity than depression (25). We obtained similar results in women at risk for cervical cancer. More precisely, higher satisfaction with the amount of sleep obtained was associated with a higher concentration of helper T-cells in circulating blood, even after controlling for depression (26).
Even though these studies provided some evidence that clinical insomnia is associated with immunity, they were characterized by some methodological flaws. One limitation was the lack of an operational definition of insomnia. Indeed, insomnia was defined more as a sleep complaint evaluated with general items rather than as an insomnia syndrome, according to standard criteria of the International Classification of Sleep Disorders (ICSD) (27) or the Diagnostic and Statistical Manual of Mental Disorder (DSM-IV) (28). Another limitation was the sampling of only one isolated immune measure, NK cell activity, which is often used because it is easier to analyze rather than because of its relevance as an indicator of overall immune function (29).
The goal of this study was to evaluate the relationship between primary chronic insomnia and immune function by comparing healthy individuals with chronic primary insomnia to age
Chrome Insomnia and Immunity 19
and sex-matched good sleepers on a variety of immune parameters. Based on the existing literature, we hypothesized that patients suffering from insomnia would display greater immunosupression than good sleepers.
METHOD Participants
Twenty participants with insomnia and 20 good sleepers aged between 18 and 45 years olds were recruited through media advertisements. The inclusion criteria for the group of Insomnia Participants (IP) were the diagnostic criteria for primary and chronic insomnia of the International Classification of Sleep Disorders (ICSD) (27) and the Diagnostic and Statistical Manual of Mental Disorder (DSM-IV) (28). Those criteria were: a) sleep-onset latency or time awake after sleep onset greater than 30 min per night, with a corresponding sleep efficiency (ratio of total sleep time to time spent in bed) lower than 85%, for a minimum of 3 nights per week; b) duration of insomnia for at least 6 months; and c) complaint of at least one negative daytime effect (e.g. fatigue, impaired functioning, or mood disturbances) attributed to poor sleep, or marked distress. Participants in the Good Sleepers (GS) condition : a) had no subjective complaints of insomnia; and b) reported sleeping between 7 and 9 hours each night. Individuals in both groups were excluded if there was evidence of: a) another sleep disorder (e.g., sleep apnea or periodic limb movements [27]), as evaluated by the Diagnostic Interview for Insomnia (30) and by polysomnography; b) a current psychiatric disorder (e.g., major depression,
substance use disorder) as evaluated by a French adaptation of the Structured Clinical Interview for DSM-IV (31) ;c) severe depressive or anxiety symptoms, as suggested by a score greater than 21 on the Beck Depression Inventory (BDI) (32) and a score greater than 30 on the Beck Anxiety Inventory (BAI) (33); d) presence of an acute or chronic medical disorder that may influence sleep or immunity; and e) recent (i.e., in the past two weeks) use of medications known to
sleep and/or immune functioning (e.g., psychotropic medications, prostaglandine inhibitors or ß- blockers). Pregnant women were also excluded.
In response to media advertisement, 143 persons requested additional information about the study. Each individual was initially screened on the basis of the inclusion and exclusion criteria, using a telephone interview. A total of 92 individuals were excluded because of lack of interest or because they met at least one of the exclusion criteria, leaving 51 potential participants who were scheduled for an interview. Forty-five participants underwent the interview. Following interview and a review of questionnaires and sleep diaries, we excluded 5 persons because they did not meet criteria for insomnia (n=2) or good sleep (n=T) or because of evidence of periodic limb movements (n=l) or mood disorder (n=l). Of the 40 participants who met all of the selection criteria for this study and had a first blood draw, 37 completed all procedures of the study. One participant was excluded because of an acute disease during the course of the study and two dropped out just before polysomnographic assessments.
The GS group was composed of 19 participants (10 males, 9 females) with a mean age of 32.4 years (range 22-44). The IP group was composed of 18 participants (8 males, 10 females) with a mean age of 34.7 years (range 18-44). IP reported either mixed sleep-onset and
maintenance insomnia (56%), sleep-onset insomnia (39%), or maintenance insomnia (5%). The average insomnia duration was 11.5 years (SD= 11.5). Participants of both groups were mostly Caucasian French Canadian (92%). Sixty percent of the total sample were single, 32% were married, and 8 % were separated or divorced. Table 1 displays demographic and lifestyle characteristics for both groups.
Chronic Insomnia and Immunity 21
Procedures
Participants selected after phone screening were invited for an interview to further assess their eligibility. In the meantime two SD forms with instructions were mailed along with the following questionnaires: the SII, the BDI, the BAI, a sociodemographic questionnaire, and a medical history questionnaire. Participants were asked to bring in the completed questionnaires at the interview. During this evaluation session written consent was obtained and two semi- structured interviews, the Diagnostic Interview for Insomnia and the Structured Clinical Interview for DSM-IV, were administered by two different trained clinicians. For participants still meeting inclusion criteria for the study, venous blood was drawn (Time 1).
Participants were asked to continue completing the sleep diary until the two consecutive nights of polysomnography, usually one week later for a total of 3 weeks of SD. A second blood draw was taken before the second night in the laboratory (Time 2). All blood was collected between 20h30 and 211130 PM to control for diurnal variation. The health practices questionnaire was completed before both blood draws. Due to technical problems, two blood samples are missing at Time 2. IP who fully completed the study were offered a cognitive-behavioural treatment of insomnia as a compensation for their participation, whereas GS received 50SCAN.
Measures
Subjective sleep assessment. The Sleep Impairment Index (SII) (34) is a seven-item
questionnaire that provides an index of insomnia severity. Participants rate the following aspects using 5-point Likert scales (“0”= not at all, “4”= extremely): a) severity of sleep-onset, sleep maintenance and early morning awakening problems; b) satisfaction with current sleep pattern ; c) interference with daily functioning; d) noticeability of impairment attributed to sleep problem;
and e) level of distress caused by the sleep problem (30). The subjective ratings provide valuable information on the patient’s perception of his or her sleep problem. The total score is obtained by adding the rating of the seven items, and ranges from 0 to 28. The French version of the SII (35) has good internal consistency (Cronbach’s alpha= 0.88) and convergent validity with total sleep time and sleep efficiency using sleep diaries is adequate (r = 0.65) (34).
The sleep diary (SD) (30) is a self-monitoring instrument that provides subjective
estimates of sleep parameters. These daily estimates yield a reliable and valid index of insomnia, even though they do not reflect absolute values obtained from polysomnography (36). The SD is completed daily upon arising for at least a two-weeks period in order to provide a relatively stable index of insomnia (30). The SD assesses the following information: a) daytime napping; b) bedtime; c) sleep-onset latency, defined as the time from initial lights-out to sleep onset; d) frequency of nocturnal awakenings; e) awakenings duration; f) wake-up time; g) arising time; h) feeling upon arising (five point-scale); and i) sleep quality (five-point scale). Sleep indices derived from the SD are: a) sleep onset latency; b) wake after sleep onset (i.e., amount of time awake from the initial sleep onset to the last awakening); c) early morning awakening (i.e., time awake from the last awakening until actual arising time); d) time in bed (i.e., total time elapsed from initial lights-out to final arising time); e) total wake time (i.e., summation of awakenings); f) total sleep time (i.e., total wake time subtracted from time in bed) and finally; g) sleep
efficiency (i.e., total sleep time divided by time in bed and multiplied by 100) (37).
Polysomnography (PSG). All participants spent 2 consecutive nights in the sleep
laboratory. Bedtime and arising time were kept as close as possible (i.e., within 30 min) to the participant’s habitual sleep schedule. A standard PSG montage that included
Chronic Insomnia and Immunity 23
monitoring was used. Sleep tracings were scored by an experienced technician according to standardised criteria (38). Respiration (i.e. air flow, tidal volume and oxygen saturation) and anteriar tibialis EMG were recorded during the first night to detect sleep apnea or periodic limb movements. Sleep variables derived from PSG were the same as those derived from the SD. Sleep onset latency was defined as the latency to the onset of stage 2 sleep (37). The first night of recording was an adaptation night and we used only the data from the second PSG assessment night for the present analyses.
Psychological measures. The Beck Depression Inventory (BDI) (32) consists of 21 items
representing various symptoms of depression. Each item includes a series of four statements reflecting different intensity of depressive symptoms. The participant indicates which statement describes best his/her state for the last seven days. A score greater than 23 was considered as an indicator of clinical depression (32). Psychometric properties of the French Canadian version are well established with an internal consistency of 0.92 (39, 40).
The Beck Anxiety Inventory (BAI) (33) is a 21-item self-report inventory which assesses the intensity of cognitive, affective and physiological symptoms of anxiety. The patient rates symptom’s intensity during the last seven days on a 0 to 3 scale. A score over 29 was considered as an indicator of clinical anxiety. The French Canadian adaptation of the BAI has good
reliability and validity properties in non-clinical samples, including an internal consistency of 0.93 (40).
Health practices. Health behaviors that may potentially confound the relationship
between insomnia and immune functioning were assessed using a questionnaire elaborated by our research team. This questionnaire assesses smoking, exercise and dietary practices as well as caffeine, drug and alcohol consumption. Present and past smoking status was assessed as well as
the number of cigarettes smoked in the past week. The exercise index evaluates energy expenditure using the 7-day recall method (42). The basis of this calculation is resting metabolism (1 MET) which is approximately equal to one kilocalorie per kilogram per hour. Moreover, kilocalorie per kilogram is calculated for the past week, according to the time spent in moderate (i.e., 4 METS; e.g.: yard work, golf), hard (i.e.,6 METS; e.g.; double tennis, disco dancing), and very hard (i.e., 10 METS; e.g.: jogging, racquetball) activities as well as the time spent asleep (i.e., 1 MET ; according to SD) and the time spent in light activity (i.e., 1.5 METS; the time of the week not included in other categories) (43). Quality of nutrition was evaluated using 8 Likert scales items (“1” = never to “5” = 7 days/week) assessing the frequency of eating breakfast and compliance with the Canada’s food Guide to healthy eating (44) (e.g., to eat between 5-10 servings of fruits and vegetables per day). Number of alcoholic drinks in the past week was based on separate estimates of weekdays and weekend days drinking. Alcohol consumption was estimated separately for the typical week as well as for the past week. A half pint, bottle, or can of beer, a glass of wine, and a shot of whisky contain approximately equal amounts of alcohol and were considered as a single drink. Caffeine intake was assessed using questions about the number of cups of different beverages consumed in the past 48 hours. This number was then multiplied by the approximate quantity of caffeine (mg) contained in each of them (45).
Immunologic Assays. For all participants, venous blood (24ml) was collected in 3
heparinized tubes. Analyses were performed by laboratory personnel who were “blind” to the clinical status of participants (insomniacs Vs good sleepers).
Lymphocyte subsets were determined in the whole blood by three-color direct immunoluorecence using a FACScan flow cytometer (FACScan, Becton Dinckinson
Chronic Insomnia and Immunity 25
Immunocytometry Systems, San Jose, CA). A minimum of 10,000 cells per sample was analysed. To analyse lymphocyte surface Ags, mAbs directly conjugated with fluorescein
isothiocyanate (FITC), phyco erythrin (PE) or peri din chlorophyll (PerCP) were used. Briefly, for each subset analysis, 10μ1 Abs (TATEST™) were added to 50 μΐ EDTA blood and incubated for 15 min. Erythrocytes were then disintegrated using OPTILYSE reagent (Coulter, ). Enumeration by flow cytometry included the following cells: T cells (CD3+; CD3 FITC), T helper cells (CD3+CD4+; CD3 FITC/CD4 PE/CD45 PerCP), T suppressor/cytotoxic cells (CD3+CD8+; CD3 FITC/CD8 PE/CD45 PerCP) and NK cells (CD3+/CD16+CD56+; CD3 FITC/CD16+CD56 PE/CD45 PerCP). All Abs and immunofluorecence reagents were purchased from Becton Dickinson (San Jose, CA).
For determination of IL-1-β, IL-2, and IFN-γ production, a whole blood assay was performed (46). Blood was drawn into syringes pre-treated with heparin. Aliquots of 50 μΐ of blood were resuspended under laminar airflow in 400 μΐ of RPMI 1640 medium ( containing 2mM L-glutamine, 100 U/ml penicillin, and 100 pg/ml streptomycin; Life Technologies, Birlington, Ontario). For stimulation of IL-1-β, 0.5 pg LPS from Escherichia coli was added, dissolved in 50 μΐ of a medium containing 80% RPMI and 20% sterile water (final
concentration, 1 pg/ml). For stimulation of 11-2 and IFN-γ, 2.5 μ g PHA was added, dissolved in 50 μΐ of a medium containing 50% RPMI and 50% sterile water (final concentration 5pg/ml). Every sample was stimulated in duplicate. Before and after each measurement, an unstimulated control was included to exclude contamination of blood and reagents. The samples were
incubated for 48h at 37°C with 5% carbon dioxide in humidified air. The supernatant were harvested and stored at -80 °C until assay. The incubation time of 48 h was chosen on the basis of previous kinetic studies indicating that this time provides good estimate for the production of
cytokines assessed in this study (47). The resultant measure of cytokines concentration, therefore, has to be regarded as a net measure of these two processes. All cytokine levels were measured by ELISA kits (Biosource International, Camarillo, CA) .The sensitivities of the assays were 1 pg/ml for IL-1-β, 5 pg/ml for IL-2 and and 4 pg/ml for IFN-γ. Data on IL-2 production on Time 1 are missing because of technical problems.
Statistical analyses
Descriptive statistics and hypothesis testing were performed using the Statistical Package for Social Sciences, version 8.0 for Windows. Bilateral tests and an alpha level of 0.05 were used for all statistical analyses. Effect sizes were reported to enable readers to evaluate the strength of the results across samples, designs, and analyses (48). Power analyses were conducted on an interactive program (PowPal) (49) that computes effect sizes and power estimates from summary statistics.
The present report focuses on sleep status (insomniac or good sleeper) and selected immune parameters (i.e., percentage of CD3, CD4, CD8, CD 16/56 and production of IL-lß, IL-2 and INF-γ) assessed at two time points. The main goal was to determine whether the two groups of participants differed significantly on these immune parameters.
We measured a series of control variables that might have confounded the relationship between sleep and immune function. These variables included age, gender, education, ponderal index, and health practices. The ponderal index was calculated using this formula:
height2/weight. We planned to statistically control for those variables that were significantly different between groups.
Chronic Insomnia and Immunity 27
RESULTS
Preliminary analyses
Two-tailed t tests and chi-square analyses were conducted to determine whether the two groups were equivalent on demographic, psychological (depression, anxiety) and health practice variables. There were no significant difference between groups on gender, age, and marital status. However, GS were significantly better educated than IP (see Table 1). Further analyses using bivariate correlations revealed no significant correlation between education and any of the immune parameters in both groups. Thus, education was not used as a covariate in the
subsequent analyses. As shown in Table 1, no significant difference was observed between insomniacs and good sleepers on any of the health-behavior variables. Consequently, they were not used as covariate in subsequent analyses. The BAI and BDI total scores were significantly greater in IP compared to GS (psO.Ol). However, we decided not to control statistically for these clinical variables because IP have often been found to report more anxious and depressed symptoms, suggesting that these mood disturbances are inherent characteristics of insomnia.
In order to validate the group assignment, the two groups were compared on the SII total score, sleep diary variables, and sleep EEG measures. These data are shown in Table 2. As expected, the IIS total score was significantly higher in IP (range - 10-25) compared to GS (range = 0-7). In addition, patients with insomnia reported significantly more sleep disturbances than good sleepers on all sleep variables, as assessed by the daily diary (psO.OOl). Although the EEG sleep of IP was generally more impaired than GS, there was no difference between groups on any EEG measure.
White blood cells counts
A multivariate analysis of variance (MANOVA) conducted on the percentage of lymphocytes-T subsets (CD3+ cells, CD4+ cells and CD8+ cells) showed no difference between groups at Time 1, F (3,33) =0.9, p = 0.43 and Time 2, F (3,29) = 1.6, p = 0.20). Power analyses revealed a medium effect size at Time 1 (d = 0.59) and a large effect size at Time 2 (d = 0.83). As shown in Table 3, two-tailed t tests revealed no difference between IP and GS on the percentage of CD3+ (T lymphocytes), CD4+ cells (T helper), CD8+ cells (T suppressor) and CD 16+/CD56+/CD3" cells (NK cells) neither at Time 1 nor at Time 2. Only the difference on the percentage of CD3+ cells approached statistical significance (p = 0.06).
Cytokines
A MANOVA conducted on IL-lß, IFN-γ and IL-2 showed no significant difference between groups at Time 2, F (3,14) =3.1, p = 0.06. However, a power analysis revealed a large effect size (d = 1.64). As shown in Table 3,11-2 production was significantly lower in GS at Time 2, t (1, 29) = 2.7, p = 0.02 with a large effect size (d =1.01). Two-tailed t tests also revealed no significant difference between IP and GS on Il-1-β and IFN-γ production at Time 1 and Time 2. Power analyses yielded small to medium effect sizes, ranging from 0.14 to 0.71. Nevertheless, this analysis indicated that 35 individuals per group would have been needed to obtain a
statistically significant difference with a conventional power level of 0.80 on production of IFN- γ at Time 1 (50).
Chronic Insomnia and Immunity 29
Immune parameters stability
Since the pattern of results appeared to vary over time, paired sample t-tests were conducted on immune parameters to verify their stability between Time 1 and Time 2. No significant difference was observed on lymphocyte percentages between Time 1 and Time 2 for the total sample (ps >0.45) and when both groups were taken separately (GS: ps >0.27; IP: ps > 0.14). However, there was a significant increase of IL-1-β and IFN-γ production from Time 1 to Time 2 for IP (ps <0.05) and for the total sample (ps < 0.05), with large effect sizes for IL-1-β (d = 0.87) and IFN-γ (d = 1.16) production. GS had stable production of IL-lß and IFN-γ between the first and second assessment period (ps > 0.33).
DISCUSSION
The goal of this study was to evaluate the relationship between primary chronic insomnia and immune functions by comparing individuals with insomnia to good sleepers on a variety of immune parameters. The only significant difference was a higher IL-2 production in patients with insomnia compared to good sleepers at Time 2. Unfortunately, IL-2 data were not available at Time 1 (because of technical problems) to determine whether this effect was stable over time. In addition, there was a nonsignificant trend for the percentage of CD3+ cells to be lower in insomniac patients at Time 2. Power analyses indicated that only a few additional participants (i.e., approximately 15 per groups) would have been needed to make this difference statistically significant. Additional power analyses revealed that many more participants would have been needed to detect a significant group effect on other immune variables measured (i.e., CD4, CDS, and NK cell percentages and IL-1-β and IFN-γ production) suggesting that, if these differences
exist, they are rather weak. Aside from IL-1-β and IFN-γ data of insomniac patients, immune parameters were stable across the two time points.
Because this study is the first to compare insomniac participants to good sleepers on immune functioning, its results are difficult to compare to those of previous studies. The most relevant studies are those conducted in the context of depression (24-26) as they were the only one examining the impact of clinical insomnia. Although those studies showed that patients with insomnia were more immunosuppressed compared to normal controls, they only evaluated NK cell activity, a variable not measured in the present study. Our results can also be compared to studies of partial sleep deprivation (PSD), although this experimental procedure may be quite different from clinical insomnia. Irwin and his collaborators observed a significant reduction of NK cells percentage and IL-2 production following an early-night PSD (21), while no effect on circulating level of IL-2 was observed after a late-night PSD (23). These findings suggest that insomnia could significantly decrease IL-2 production. However, the opposite result was observed in the present study, that is insomniac participants had increased IL-2 production compared to good sleepers. However, it is likely that our IL-2 production measure at Time 2 was affected by the sleep laboratory assessment conducted the preceding night. Indeed, good sleepers tended to sleep worse while insomniac participants tended to sleep better in the sleep laboratory, compared to their usual sleep at home. Further, the stress associated with sleeping in the
laboratory might also have confounded the relationship between insomnia and immunity. Surprisingly, our results are more consistent with findings of total sleep deprivation (TSD) studies. The literature review of Dinges and his collaborators (20) suggests that, despite some inconsistencies, TSD generally increases cytokines production. However, it remains intriguing that our groups only differ significantly on one immune parameter.
Chronic Insomnia and Immunity 31
The group difference on only one immune variable can also be explained by the absence of clear difference between groups on EEG sleep measures. Indeed, no statistically significant difference was observed between good sleepers and insomniac participants on sleep laboratory data. Participants were selected for the study according to subjective sleep assessments based on a clinical interview and daily sleep diary monitoring but not based on sleep laboratory results. Therefore, it is plausible that more differences on immune functioning would have been observed between good and poor sleepers, if their status had been validated by
polysomnographic assessment. However, the sleep patterns of good sleepers and insomniac patients is often different in the sleep laboratory, especially during their first night spent in the laboratory (51). Insomniacs tend to sleep better in sleep laboratory, whereas good sleepers typically sleep worse, as was also found in this study. A recent study concluded that a week of recording may be necessary to achieve adequate temporal stability of polysomnographic data in elderly insomniacs (52). In the present study, participants slept only 2 nights in the laboratory, which may not have been sufficient to reliably assess sleep.
Another possible explanation for our negative results is that some parameters (e.g., white blood cells subsets) measured in the peripheral blood may vary significantly depending on the circadian time of blood testing (53). A recent study (54) showed that the levels of IL-6 can be either higher or lower during the post-deprivation period compared to pre-deprivation values, depending on the time of testing (i.e., daytime and nighttime). Hence, it is likely that insomnia also has a biphasic effect on IL-2 production and that our results are only indicative of effects occurring during nighttime.
Despite these limitations, the present study offers some methodological improvements compared to previous studies. First, we evaluated various immune parameters simultaneously in
order to obtain a more general measure of immune functioning. Compared to previous studies that used a single measurement point of immunity, we evaluated these parameters twice, with a week interval, which allowed to measure temporal stability. Very few psychoneuroimmunology studies have done this before. Moreover, several demographic and health behavior variables that could have confounded the relationship between insomnia and immunity were evaluated, with the intention to control for the variables on which the two groups would have differed
significantly. According to our preliminary analyses, this control proved to be unnecessary. Areas for future research include the selection of more clinically meaningful immune variables and repeated measurements of those variables. Firstly, assessment of cells from
peripheral blood samples presents serious interpretation problems because conventional immune responses are developed in secondary lymphoid organs (lymph nodes, spleen, etc.) and not from cell circulation. Thus, changes in functional activities of peripheral blood lymphocytes might simply reflect a redeployment of cells to sites where they are needed the most. Assessment of mucosal immunity (which represents 20-50% of the body’s total lymphocytes) could represent a better alternative to study sleep-immunity relationships, but is not as practical (29).
Secondly, our results suggest that immune parameters can vary considerably within a week period of time. Because of this variability, it is probably unrealistic to pretend that one or two measures reliably reflects the general immune functions of an individual. The vast majority of psychoneuroimmunogy studies used only one immunological measurement. A better approach would be to take repeated immune measures (e.g., daily or weekly) or to take continuous
measures (e.g., every hours) as it is often done in circadian rhythm studies. Another area of future research is to evaluate the short-term effects of sleep loss (i.e., bad night Vs good night) on immunity during the following days. Indeed, it may be that insomnia does not lead to chronic
Chronic Insomnia and Immunity 33
immunosuppression but rather produces a short-term immune-down regulation that stabilizes during the recovery period.
In sum, the present study suggests that good sleepers have lower IL-2 production compared to insomniac participants but the groups do not differ significantly on any other immune measures taken in this study. These findings are inconsistent with previous studies conducted on depression and partial sleep deprivation. Several possible hypotheses were raised to explain those discrepancies and several areas were suggested to extend this line of research.
REFERENCES
1. Ford DE, Kamerow DB: Epidemiologic study of sleep disturbances and psychiatric disorders. JAMA 262: 14791989 ,1484־
2. Gallup Organization: Sleep in America. Princeton, NJ: Author, 1991
3. Mellinger GD, Balter MB, Uhlenhuth EH: . Insomnia and its treatment: Prevalence and correlates. Arch of Gen Psychiatry 42: 2251985 ,232־
4. Wereyer S, Dilling H: Prevalence and treatment of insomnia in the community: Results from the upper Bavarian field study. Sleep 14: 3921991 ,398־
5. Lavie P: Sleep habits and sleep disturbances in industrial workers in Israël: Main findings and some characteristics of workers complaining of excessive daytime sleepiness. Sleep 4: 147-158, 1981
6. Bixler EO, Kales A, Soldatos C, et al: Prevalence of sleep disorders in the Los Angeles metropolitan area. Am J Psychiatry 4: 12571262,1979־
7. Healey ES, Kales N, Monroe LJ, Bixler EO, Chamberlin K, Soldatos CR: Onset of insomnia: Role of life stress events. Psychosom Med 43: 4391981 ,451־
8. Kales JD, Kales A, Bixler EO et al: Biobehavioral correlates of insomnia V: clinical characteristics and behavioral correlates. Am J Psychiatry 141: 1371-1376, 1984
9. Kuppermann M, Lubeck DP, Mazonson PD et al: Sleep problems and their correlates in a working population. J Gen Intern Med 10: 251995 ,32־
10. Johnson LC, Spinweber CL: Quality of sleep and performance in the Navy: A longitudinal study of good and poor sleepers. In: Guileminault C, Lugares! E, eds. Sleep-wake disorders: natural history, epidemiology, and long term evolution. New-York: Raven Press: 131983 ,28־ 11. Krueger JM, Toth LA: Cytokines as regulators of sleep. Ann of N־Y Acad Sei 739: 299310־,
1994
12. Krueger JM, Majde JA: Sleep as a host defense: Its regulation by microbial products and cytokines. Clin Immunol Immunopathol 57: 188-199, 1990
13. Krueger JM, Majde JA: Cytokines and sleep. Int Arch of Allergy and Immunol 106: 97100־, 1995
14. Curti R, Radice GC, Cesana R, Grieco A: Work, stress and immune system: Lymphocyte reactions during rotating shift work. Med Lav 6: 564-570, 1982
Chronic Insomnia and Immunity 35
15. Nakano Y et al: The effect of shift work on cellular immune function. J Human Ergol 11(8):131-137, 1982
16. Kripke DF, Simons RN, Garfinkel L, Hammond C: Short and long sleep and sleeping pills: Is increased mortality associated? Arch of Gen Psychiatry 36: 103-116, 1979
17. Wingard DL, Berkman LF: Mortality risk associated with sleeping patterns among adults. Sleep 6: 102-107, 1983
18. Everson CA: Sustained sleep deprivation impairs host defense. Am J of Physiol 265: R1148- R1154, 1993
19. Brown R, Price RJ, King M, Husband A J: Interleukin-1 ß and muramyl dipeptide can prevent decreased antibody response associated with sleep deprivation. Brain, Beh, and Imm 3: 320-330,1989
20. Dinges, DF, Douglas SD, Hamarman S, Zauggi L, Kapoor S: Sleep deprivation and human immune function. Adv in Neuroimmunology 5: 97-110, 1995
21. Irwin M, McClintick J, Costlow C, Fortner M, White J, Gillin JC: Partial night sleep deprivation reduces natural killer and cellular immune responses in humans. FASEB J 10: 643-653,1996
22. Irwin M, Maschovich A, Gillin CJ, Willoughby R, Pike J, Smith TL: Partial sleep
deprivation reduces natural killer cell activity in humans. Psychosom Med 56: 493-498, 1994 23. Irwin M, Thompson J, Miller C, Gillin C, Ziegler M: Effects of sleep and sleep deprivation
on catecholamine and interleukine-2 levels in human: Clinical implications. J of Clin Endocri and Metabolism 84: 1979-1985, 1999
24. Irwin M, Smith TL, Gillin CJ: Electroencephalographic sleep and natural killer activity in depressed patients and control subjects. Psychosom Med 54: 10-21, 1992
25. Cover H, Irwin M: Immunity and depression: Insomnia, retardation, and reduction of natural killer cell activity. J of Beh Med, 17: 217-223, 1994
26. Savard J et al.: Association between subjective sleep quality and depression on
immunocompétence in low-income women at risk for cervical cancer. Psychosom Med 6: 496-507,1999
27. American Sleep Disorders Association (ASDA): International classification of sleep disorders (ICSD): Diagnostic and coding manual. Rochester, MN: Author, 1990
28. American Psychiatric Association (APA): Diagnostic and statistical manual of mental disorders (4th ed.). Washington, DC: Author, 1994
29. Benca RM, Quintans J: Sleep and host defenses: A review. Sleep 20: 1027-1036, 1997 30. Morin, CM: Insomnia: Psychological assessment and management. New York: Guilford
Press, 1993
31. Spitzer RL, Williams JBW, Gibbon M, First MB: SCID. User’s guide for the Structured Clinical Interview for DSM-IIIR. Washington, DC: American Psychiatric Press Inc., 1990 32. Beck AT, Steer RA, Garbin MG: Psychometric properties of the Beck Depression Inventory:
Twenty-five years of evaluation. Clin Psycho Review 8: 77-100, 1988
33. Beck AT, Epstein N, Brown G, Steer R: An inventory for measuring clinical anxiety: Psychometric properties. J of Consult and Clin Psycho 56: 893-897, 1988
34. Morin CM, Azrin NH: Social and clinical validation of insomnia treatment outcome. Paper presented at the meeting of the Association for Advancement of Behavior Therapy, Houston, TX, 1985
35. Blais FC, Gendron L, Mimeault V, Morin CM: Évaluation de l’insomnie: Validation de trois questionnaires [Evaluation of insomnia: Validation of three questionnaires], L’Encéphale 23: 447-453, 1997
36. Coates TJ, Killen JD, George J, Marchine E, Silverman S, Thoresen C: Estimating sleep parameters: A multitrait-multimethod analysis. J of Consult and Clin Psycho 50: 345-352,
1982
37. Morin CM, Kowatch RA, Barry T, Walton E: Cognitive-behavior therapy for late-life insomnia. J of Consult and Clin Psycho 61:137-146, 1993
38. Rechtschaffen A, Kales A: A manual of standardized terminology, techniques, and scoring system for sleep stages of human subjects. Los Angeles, CA: BIS/BRI, 1968
39. Bourque P, Beaudette D: Étude psychométrique du questionnaire de dépression de Beck auprès d’un échantillon d’étudiants universitaires et francophones. Can J of Beh Scie 14: 211-218,1982
40. Gauthier J, Morin C, Thériault F, Lawson JS: Adaptation française d’une mesure d’auto- évaluation de l’intensité de la dépression. Rev Québécoise de Psycho 3: 13-27, 1982.
4L Freeston MH, Ladouceur R, Thibodeau N, Gagnon F, Rhéaume J: L’inventaire d’anxiété de Beck. Propriétés psychométriques d’une traduction française. L’Encéphale 20: 47-55, 1994
Chronic Insomnia and Immunity 37
. Blair SN: How to assess exercise habits and physical fitness. In Behavioral health. Handbook of enhancement and disease prevention, ed. Matarazzo JD, Herd JA, Miller NE, Weiss SM. New York: Willey, 424-447, 1984
. Ross RM, Jackson AS: Exercise concepts, calculations, and computer application. Carmel: IN: Benchmark Press, 1990
. Health Canada: Canada’s food Guide to healthy eating. Canadian government publication, 1998
. Barone JJ, Roberts H: Human consumption of caffeine. In Perspective from recent research, ed. Dews PB. Berlin: Springer-Verlag, 59-85, 1984
. Kirchner H, Kleinicke C, Digel W: A whole-blood technique for testing production of human interferon by leukocytes. J Immunol Methods 48: 213, 1982
. De Groote D et al: Direct stimulation of cytokines (IL-1-β, TNF-a, IL-6, IL-2, IFN-γ and GM-CSF) in whole blood. Comparison with isolated PBMC stimulation. Cytokine 4: 239, 1992
. Wilkinson L et al: Statistical methods in psychology journals. Guidelines and explanation. Am Psychologist 54: 594-604, 1999
. Gordman BS, Premavera LH, Allison DB: PawPal: A program for estimating effect sizes, statistical power, and sample sizes. Edu & Psy Measurements 55: 773-776
. Cohen J: Statistical power analysis for the behavioral sciences (2nd ed.), Hillsdale, NJ: Erlbaum, 1988
. Karacan I, Williams RL, Littell RC, Sallis PJ: Insomniacs: Unpredictable and idiosyncratic sleepers. In: Sleep: Physiology, biochemistry, psychologoly, pharmacology, clinical
implications. First European Congress of Sleep research, Basel: 120-132, 1972
. Wohlgemuth WK, Edinger JD, Fins AI, Sullivan RJ: How many nights are enough? The short term stability of sleep parameters in elderly insomniacs and normal sleepers. Psychophysiology 36: 233-244, 1999
. Bom J, Lange T, Hansen K, Molle M, Fehm H-L: Effects of sleep and circadian rhythm on human circulating immune cells. J of Immunol 158: 4454-4464, 1997
. Vgontzas AN et al: Circadian interleukin-6 secretion and quantity and depth of sleep. J of Clin Endocri and Metabolism 84: 2603-2607, 1999
42 43 44 45. 46. 47, 48. 49, 50. 51. 52. 53. 54.
TABLE 1. Demographic, Psychological, and Health Practice Variables of Insomnia Participants and Good Sleepers.
Insomnia Good
Variables Participants Sleepers
n==18 n==19 t if d Mean SD Mean SD Demographic variables Age (years) 34.7 8.5 32.4 6.8 0.9 0.38 0.30 Education (years) 15.5 2.9 17.5 2.8 2.2 0.04 0.74 Psychological variables
Beck Anxiety Inventory 11.0 6.8 5.2 5.9 3.3 0.002 1.12
Beck Depression Inventory 10.9 7.2 4.3 4.5 2.8 0.008 0.95
Health practice variables Ponderal Index (m2/Kg)
24.1 2.6 22.9 4.2 1.1 0.29 0.37
Energy expenditure (kcal/kg*wl) 251.2 34.2 246.5 22.7 0.5 0.64 0.17 Energy expenditure(kcal/kg*w2) 239.0 16.2 240.3 11.6 0.3 0.79 0.10 Mean caffeine intake/day (mg) 143.1 135.2 180.1 140.9 0.8 0.43 0.27
Dietary Habit Index 34.8 6.2 33.1 6.7 0.8 0.43 0.27
Alcohol consumption
No. drinks past week (Tl) 3.1 4.1 3.4 4.0 0.2 0.81 0.07
No. drinks past week (T2) 3.4 4.8 3.7 4.5 0.2 0.84 0.07
Mean No. drinks/week 2.1 2.5 3.3 2.6 1.5 0.15 0.51
