Journal
AMERICAN JOURNAL OF PHYSIOLOGY-ENDOCRINOLOGY AND METABOLISM
Volume 282, Issue 2, Pages E297-E303Publisher
AMER PHYSIOLOGICAL SOC
DOI: 10.1152/ajpendo.00268.2001
Keywords
aging; biological rhythms; chronobiology; constant routine
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Funding
- NCRR NIH HHS [M01 RR-02635] Funding Source: Medline
- NIA NIH HHS [R01 AG-06072, P01 AG009975, P01 AG-09975] Funding Source: Medline
- NIMH NIH HHS [R01 MH-45130] Funding Source: Medline
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We investigated the relationship between sleep timing and the timing of the circadian rhythm of plasma melatonin secretion in a group of healthy young and older subjects without sleep complaints. The timing of sleep and the phase of the circadian melatonin rhythm were earlier in the older subjects. The relationship between the plasma melatonin rhythm and the timing of sleep was such that the older subjects were sleeping and waking earlier relative to their nightly melatonin secretory episode. Consequently, the older subjects were waking at a time when they had higher relative melatonin levels, in contrast with younger subjects, whose melatonin levels were relatively lower by wake time. Our findings indicate that aging is associated not only with an advance of sleep timing and the timing of circadian rhythms but also with a change in the internal phase relationship between the sleep-wake cycle and the output of the circadian pacemaker. In healthy older subjects, the relative timing of the melatonin rhythm with respect to sleep may not play a causal role in sleep disruption.
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