Effects of acutely displaced sleep on testosterone.

CONTEXT It is not yet clear whether the diurnal variation in testosterone is regulated by circadian or homeostatic (sleep) influences. OBJECTIVE The present study tested whether testosterone is driven by a circadian-independent sleep effect by shifting sleep acutely to daytime in a 24-h sampling regiment. DESIGN, SETTING, AND PARTICIPANTS In the sleep laboratory, seven healthy young men (age, 22-32 yr) participated in three conditions: habituation (sleep between 2300-0700 h), night sleep (2300-0700 h), and day sleep (0700-1500 h), the latter two in a balanced order. INTERVENTION AND MAIN OUTCOME MEASURE Serum testosterone was, in all conditions, sampled by hourly blood drawing for 24 h during constant bed rest. RESULTS Mean testosterone levels increased as a log-linear function of time (hours) across both sleep periods (b = 4.88; P < 0.001), from 15.3 +/- 2.1 to 25.3 +/- 2.2 nmol/liter during night sleep and from 17.3 +/- 2.1 to 26.4 +/- 2.9 nmol/liter during day sleep. Similarly, mean testosterone levels decreased with time (log-linear) awake (b = -1.80; P < 0.001). There was also evidence of a weak circadian component (acrophase ranging between 0651-0924 h) and an increase with time in the laboratory. Moreover, all these effects, except for the increase during sleep, differed significantly between individuals. CONCLUSION In conclusion, testosterone increased during sleep and fell during waking, whereas circadian effects seemed marginal. Individual differences were pronounced.