254 Sleep as a Mediator of the Relationship between Socioeconomic Status and Health: A Hypothesis EVE VAN CAUTER a AND KARINE SPIEGEL Department of Medicine, University of Chicago, 5841 South Maryland Avenue, Chicago, Illinois, USA Laboratory of Experimental Medicine, Université Libre de Bruxelles, Belgium ABSTRACT: This article discusses the hypothesis that the adverse impact of low socioeconomic status (SES) on health may be partly mediated by decrements in sleep duration and quality. Low SES is frequently associated with a dimin- ished opportunity to obtain sufficient sleep or with environmental conditions that compromise sleep quality. In a recent study, we examined carbohydrate metabolism, endocrine function, and sympatho-vagal balance in young, healthy adults studied after restricting sleep to four hours per night for six nights as compared to a fully rested condition obtained by extending the bed- time period to 12 hours per night for six nights. The state of sleep debt was associated with decreased glucose tolerance, elevated evening cortisol levels, and increased sympathetic activity. The alterations in glucose tolerance and hypothalamo–pituitary–adrenal function were qualitatively and quantitative- ly similar to those observed in normal aging. These results indicate that sleep loss can increase the “allostatic load” and facilitate the development of chronic conditions, such as obesity, diabetes, and hypertension, which have an in- creased prevalence in low SES groups. THE SES–HEALTH GRADIENT AND SLEEP LOSS: A HYPOTHESIS The pathways underlying the relationship between socioeconomic status (SES) and health are likely to involve multiple physiological systems. In this volume, path- ways involving cardiovascular mechanisms, immune mechanisms, and neuroendo- crine and metabolic effects of stress are discussed. As indicated in other chapters, the burden of negative emotions in low-SES groups and the erosion of psychosocial re- sources that often accompany low-SES status are also thought to be involved in the linear gradient between SES and health. In recent years, evidence has rapidly accu- mulated to indicate that sleep loss may have adverse effects on cardiovascular func- tion, on immune function, on endocrine function (particularly on the stress- responsive hypothalamo–pituitary–adrenal [HPA] system) and on carbohydrate metabolism. The negative impact of sleep loss on mood and affect has been long rec- ognized. Increased irritability has also been noted in a majority of studies involving a Address for correspondence: Eve Van Cauter, Ph.D., Department of Medicine, MC 1027, University of Chicago, 5841 South Maryland Ave., Chicago, IL 60637, USA. 773-702-0169 (voice); 773-702-9194 (fax). e-mail: evcauter@medicine.bsd.uchicago.edu