Impaired Nighttime Sleep in Healthy Old<i>Versus</i>Young Adults Is Associated with Elevated Plasma Interleukin-6 and Cortisol Levels: Physiologic and Therapeutic Implications

IL-6 and TNFα secretion is increased by sleep loss or restriction. IL-6 secretion progressively increases with age, yet its association with decreased quality and quantity of sleep in old adults is unknown. This study examined the alteration of 24-h secretory pattern of IL-6, TNFα, and cortisol in 15 young and 13 old normal sleepers who were recorded in the sleep laboratory for four consecutive nights. Serial 24-h plasma measures of IL-6, TNFα, and cortisol were obtained during the fourth day, and daytime sleepiness was assessed with the multiple sleep latency test. Old adults, compared with young subjects, slept poorly at night (wake time and percentage stage 1 sleep were increased, whereas their percentage slow wave sleep and percentage sleep time were decreased, P < 0.05). Accordingly, their daytime sleep latency was longer than in young adults (P < 0.05). The mean 24-h IL-6 and cortisol levels were significantly higher in old than young adults (P < 0.05). In both groups, IL-6 and cortisol plasma concentrations were positively associated with total wake time, with a stronger association of IL-6 and cortisol with total wake time in the older individuals (P < 0.05); their combined effect was additive. IL-6 had a negative association with rapid eye movement (REM) sleep only in the young (P < 0.05), but cortisol was associated negatively with REM sleep both in the young and old, with a stronger effect in the young. We conclude that in healthy adults, age-related alterations in nocturnal wake time and daytime sleepiness are associated with elevations of both plasma IL-6 and cortisol concentrations, but REM sleep decline with age is primarily associated with cortisol increases.