Circadian interleukin-6 secretion and quantity and depth of sleep

Patients with pathologically increased daytime sleepiness and fatigue have elevated levels of circulating interleukin-6 (IL-6). The latter is an infla mmatory cytokine, which causes sickness manifestations, including somnolenc e and fatigue, and activation of the hy pothalamic-pituitary-adrenal axis. In this study, we examined: 1) the relation between serial measurements of plasma IL-6 and quantity and depth of sleep, evaluated by polysomnography; and 2) the effects of sleep deprivation on the nyctohemeral pattern of IL-6 secretion. Eight healthy young male volunteers were sampled for 24 h twice , at the baseline state, after a normal night's sleep and after total overn ight sleep deprivation. At the baseline state, IL-6 was secreted in a bipha sic circadian pattern with two nadirs at 0800 and 2100 and two zeniths at 1 900 and 0500 (P < 0.01). The baseline amount of sleep correlated negatively with the overall daytime secretion of the cytokine (P < 0.05). Also, depth of sleep at baseline correlated negatively with the postdeprivation increa se of daytime secretion of IL-6 (P < 0.05). Sleep deprivation changed the t emporal pattern of circadian IL-6 secretion but not the overall amount. Ind eed, during the postdeprivation period, the mean daytime (0800-2200 h) leve ls of IL-6 were significantly higher (P < 0.05), whereas the nighttime (220 0-0600 h) levels were lower than the predeprivation values. Thus, sleep-dep rived subjects had daytime oversecretion and nighttime undersecretion of IL -6; the former might be responsible for their daylong somnolence and fatigu e, the latter for the better quality (depth) of their sleep. These data sug gest that a good night's sleep is associated with decreased daytime secreti on of IL-6 and a good sense of wellbeing and that good sleep is associated with decreased exposure of tissues to the proinflammatory and potentially d etrimental actions of IL-6. Sleep deprivation increases daytime IL-6 and ca uses somnolence and fatigue during the next day, whereas postdeprivation de creases nighttime IL-6 and is associated with deeper sleep.