The aging clock: circadian rhythms and later life
Suzanne Hood, Shimon Amir
Suzanne Hood, Shimon Amir
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Review

The aging clock: circadian rhythms and later life

Abstract

Circadian rhythms play an influential role in nearly all aspects of physiology and behavior in the vast majority of species on Earth. The biological clockwork that regulates these rhythms is dynamic over the lifespan: rhythmic activities such as sleep/wake patterns change markedly as we age, and in many cases they become increasingly fragmented. Given that prolonged disruptions of normal rhythms are highly detrimental to health, deeper knowledge of how our biological clocks change with age may create valuable opportunities to improve health and longevity for an aging global population. In this Review, we synthesize key findings from the study of circadian rhythms in later life, identify patterns of change documented to date, and review potential physiological mechanisms that may underlie these changes.

Authors

Suzanne Hood, Shimon Amir

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Figure 3

Schematic of possible mechanisms underlying age-related changes in circadian rhythms.

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Schematic of possible mechanisms underlying age-related changes in circa...
Progressive yellowing and thickening of the lens may reduce sensitivity to light, the strongest zeitgeber. Reduction of AVP and VIP expression and fewer GABAergic synapses may decrease signaling within the SCN, leading to a decrease in the overall amplitude of its firing rhythm. A weaker SCN output signal may in turn reduce the strength of downstream oscillators in central and peripheral tissues, including the cortex, pineal gland, liver, kidney, thyroid, and spleen. Providing other zeitgebers such as scheduled meals (green arrows), which act on the circadian system via extra-SCN pathways, may help entrain an aging circadian system.