Sleep timing may modulate the effect of sleep loss on testosterone

Summary Background Sleep loss has been shown to reduce secretory activity of the pituitary–gonadal axis in men, but the determinants of this effect are unknown. Objective To discriminate the effects of sleep duration and sleep timing on serum concentrations of luteinizing hormone (LH), testosterone (T) and prolactin (PRL). Methods Fifteen young, healthy men (27·1 ± 1·3 years; BMI, 22·9 ± 0·3 kg/m2) were examined in a condition of sleep time restriction to 4 h (bedtime, 02:45 –07:00 h) for two consecutive nights and in a control condition of 8 h regular sleep (bedtime, 22:45–07:00 h). After the second night, serum concentrations of LH, T and PRL were monitored over a 15‐h period. In addition, these hormones were measured in serum samples obtained in a further experiment in eight healthy men (24·5 ± 1·1 years; BMI, 23·7 ± 0·6 kg/m2) in the morning after one night of total sleep deprivation, of 4·5 h sleep (bedtime, 22:30–03:30 h), and of regular 7 h sleep (bedtime, 22:30–06:00 h). Results Serum LH, T and PRL concentrations showed characteristic diurnal variations across the 15‐h period without any differences between the 4‐ and 8‐h sleep conditions. However, total sleep deprivation and 4·5 h of sleep restricted to the first night‐half markedly decreased morning T and PRL concentrations (both P ≤ 0·05). Conclusion Collectively, our data suggest that the effect of sleep restriction on pituitary–gonadal secretory activity may be modulated by sleep timing. While sleep loss in the early part of the night does not affect T and PRL, early awakening and wakefulness during the second part of the night reduces morning circulating T and PRL concentrations.