Effects of Aging on the Intrinsic Circadian Period of Totally Blind Humans

Abstract

Age-related changes in the intrinsic circadian period (tau) have been hypothesized to account for sleep symptoms in the elderly such as early morning awakening. The authors sought to determine whether the aging process produced quantifiable differences in the tau of totally blind men who had free-running circadian rhythms. The melatonin onset was used as the indicator of circadian phase. Melatonin rhythms had been characterized about a decade previously when the participants were 38 +/- 6 (SD) years old. Both previous and current assessments of tau were derived from at least 3 serial measurements of the 24-h melatonin profile from which the melatonin onset was determined. All 6 participants exhibited a longer tau in the 2nd assessment (mean increase +/- SD of 0.13 +/- 0.08 h; p < 0.01). Four participants exhibited differences in tau with nonoverlapping 95% confidence intervals. The results do not support the commonly held view that tau shortens during human aging. On the contrary, tau appears to slightly, but significantly, lengthen during at least 1 decade in midlife.

Aging and Circadian Rhythms

“…An initial series of forced desynchrony studies in which circadian period was assessed in healthy older adults and compared with young adults found no difference in period with age [64], and in a follow-up study of a larger group of young and older adults we found the same result [70]. A study of six blind men who each had their period estimated twice over a ~10-year interval found no evidence for a shortening of period with age within an individual [113]. Together, these findings suggest that an age-related shortening of circadian period does not underlie the advance in circadian rhythms and sleep timing with age in humans.…”

Ontogeny and aging of the distal skin temperature rhythm in humans

“…In terms of the endogenous component, there is some evidence of a shorter free-running rhythm for core temperature in older people under a constant routine protocol Harper et al 2005). However, other studies have failed to find a significant phase advance in aged people when studied under these experimental conditions (Kendall et al 2001). Although we cannot discard the possibility that their body clock is simply running faster, more reliable explanations take into account the exogenous contribution to circadian rhythms.…”

Effects of age on circadian rhythms are similar in wild-type and heterozygous Clock mutant mice

“…Experiments on the effects of age on τ in other species are also conflicting: for example, there are several reports of a shortening of τ in old golden hamsters [16,18,21,23], although one recent report found no significant age-related change in τ in the same species [6]. Similarly, in humans, there are recent reports of both changes [9] and lack of changes [5] in τ with advancing age. The effect of age on τ appears to be subtle at best; when it has been found the magnitude of the change in τ is often on the order of 0.5 h or less.…”