AN INFLAMMATORY STATE IS KNOWN TO EXIST IN SLEEP DISORDERS.1,2 INTERLEUKIN-6 (IL-6), FOR EXAMPLE, IS AN INFLAMMATORY CYTOKINE THAT IS elevated in sleep apnea and narcolepsy.3-5 Better sleep is associated with decreased daytime secretion of IL-6, whereas disturbed

729 AN INFLAMMATORY STATE IS KNOWN TO EXIST IN SLEEP DISORDERS.1,2 INTERLEUKIN-6 (IL-6), FOR EXAMPLE, IS AN INFLAMMATORY CYTOKINE THAT IS elevated in sleep apnea and narcolepsy.3-5 Better sleep is associated with decreased daytime secretion of IL-6, whereas disturbed nocturnal sleep is associated with increased daytime IL-6 levels.6 Other markers of inflammation, including plasma endothelin-1 (ET-1) and the circulating soluble form of ICAM-1 (sICAM-1) may also be elevated in the setting of sleep disorders.7,8 ET-1 is a potent vasoconstrictor and mediator of inflammation elicited from endothelial cells.10 ICAM-1 is a ubiquitously expressed adhesion molecule important for leukocyte trafficking and basic inflammatory processes.9 In contrast to the literature on sleep and cytokines, such as IL-6 and IL-1ß, the linkages between elevated levels of ET-1 and sICAM-1 and disturbed sleep are less clear. It is known that sleep disorders are associated with increased risk for coronary artery disease and that inflammation is a potential mechanism of this increased risk.11 The elevated circulating levels of IL-6 in obstructive sleep apnea are correlated with carotid intima-media thickness, suggesting that apnea-related systemic inflammation is associated with progression of atherosclerosis and increased risk of cardiovascular morbidity in these patients.12 The elevated sICAM-1 levels in patients with ischemic heart disease and sleep apnea increase their risk of atherosclerosis.13 Circulating ET-1 levels are likely elevated in obstructive sleep apnea and provide a link with increased risk for cardiovascular diseases.14,15 Like sleep disorders, even sleep disturbances in the normal range have been associated with risk for coronary artery disease and might share similar inflammatory mechanisms.16,17 In healthy adults, a modest amount of sleep loss leads to an inflammatory response that could support basic cardiovascular diseases processes.18,19 Moderately elevated levels of IL-6 and sICAM-1 are associated with increased morbidity and mortality independent of other established risk factors.20 The purpose of this study was to examine if the quality of sleep in relatively healthy individuals without a known sleep disorder is associated with inflammation. We assessed circulating levels of IL-6, sICAM-1, and ET-1 and a standard battery of polysomnography-derived indexes of sleep in a group of healthy men and women.