Sleep cycles are known to change as we get older, but circadian rhythms control deeper mechanisms like cognition and metabolism too. These internal rhythms are controlled by particular gene expression, and it appears this expression shifts in our later years - having knock on effects on multiple biological processes.
"Studies have reported that older adults tend to perform complex cognitive tasks better in the morning and get worse through the day. We know also that the circadian rhythm changes with ageing, leading to awakening earlier in the morning, fewer hours of sleep and less robust body temperature rhythms"
Researchers examined samples from 146 donated human brains, and discovered there were 235 core genes involved with this molecular clock. In the over 60s, there was a definite loss of classical rhythm but curiously the researchers found new genes gained rhythmicity too - activating a new kind of cycle. In the younger individuals, gene expression modeled the classical sleep/wake cycle.
"As we expected, younger people had that daily rhythm in all the classic 'clock' genes, but there was a loss of rhythm in many of these genes in older people, which might explain some of the alterations that occur in sleep, cognition and mood in later life"
It's not definitively clear exactly why this new cycle begins to dominate, or why the old one changes through the years. It may be that due to damage or dysregulation a new clock attempts to compensate, but that finding ways to realign rhythm to a more youthful profile could lead to beneficial changes in energy, mood, cognition and overall health.
"Since depression is associated with accelerated molecular ageing, and with disruptions in daily routines, these results also may shed light on molecular changes occurring in adults with depression"
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