Plasma melatonin rhythms in young and older humans during sleep, sleep deprivation, and wake

Study objectives: To determine the effects of sleep and sleep deprivation on plasma melatonin concentrations in humans and whether these effects are age-dependent.
Design: At least 2 weeks of regular at-home, sleep/wake schedule followed by 3 baseline days in the laboratory and at least one constant routine (sleep deprivation).
Setting: General Clinical Research Center (GCRC), Brigham and Women's Hospital, Boston, MA.
Participants: In Study 1, one group (<10 lux when awake) of 19 young men (18-30 y) plus a second group (<2 lux when awake) of 15 young men (20-28 y) and 10 young women (19-27 y); in Study 2, 90 young men (18-30 y), 18 older women (65-81 y), and 11 older men (64-75 y). All participants were in good health, as determined by medical and psychological screening.
Interventions: One to three constant routines with interspersed inversion of the sleep/wake cycle in those with multiple constant routines.
Measurements and results: Examination of plasma melatonin concentrations and core body temperature. Study 1. There was a small, but significant effect of sleep deprivation of up to 50 hours on melatonin concentrations (increase of 9.81 +/- 3.73%, P <0.05, compared to normally timed melatonin). There was also an effect of circadian phase angle with the prior sleep episode, such that if melatonin onset occurred <8 hours after wake time, the amplitude was significantly lower (22.4% +/- 4.79%, P <0.001). Study 2. In comparing melatonin concentrations during sleep to the same hours during constant wakefulness, in young men, melatonin amplitude was 6.7% +/- 2.1% higher(P <0.001) during the sleep episode. In older men, melatonin amplitude was 37.0% +/- 12.5% lower (P <0.05) during the sleep episode and in older women, melatonin amplitude was non-significantly 10.9% +/- 8.38% lower (P = 0.13) during the sleep episode.
Conclusions: Both sleep and sleep deprivation likely influence melatonin amplitude, and the effect of sleep on melatonin appears to be age dependent.
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