Short-term SD (3 h sleep/night for 4 consecutive days), in young adults, seems to be related with a significant decrease in morning serum Nutlin-3a levels [162]. This hormone decreases more after four nights of sleep loss in the earlier-night sleep restriction group (sleep from 00:00 to 03:00) than in the later-night group (sleep from 03:00 to 06:00). Data in this study suggested that SD, especially in the later night, differentially inhibits the activation of HPA-axis and reduces cortisol secretion, pointing out the importance of sleep at the 03:00 to 06:00 period, during the circadian nadir, in protecting normal physiological rhythms and function of the HPA-axis.
On the contrary, chronic SD is associated with an elevation in evening cortisol levels that may reflect decreased efficacy of the negative feedback regulation of the HPA axis. This elevation may result in a significant glucocorticoid overload [4].
Few investigators have tried to correlate cortisol secretion with sleep impairment in the elderly. Prinz and colleagues measured the 24-h urine-free cortisol levels in 88 healthy, old, non-obese men and women (mean age of 70.6 years) and observed that subjects with higher cortisol levels had more impaired sleep (lower sleep efficiency, fewer minutes of stages 2, 3, and 4 sleep, and more EEG beta activity during NREM sleep) [163].
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Distribution patterns Although both species are considered
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