24-Hour Rest-Activity Rhythms and Epigenetic Age Acceleration

1. More regular 24-hour rhythms were linked to a more favorable epigenetic aging profile

Across the different measures, the overall pattern was clear: stronger and more stable activity-rest rhythms were associated with less epigenetic age acceleration.

The clearest associations appeared with GrimAge and PhenoAge, two of the four epigenetic clocks examined in the study.

2. A stronger distinction between activity and rest was associated with less accelerated aging

People with a clearer difference between their more active and less active periods tended to have more favorable epigenetic-aging results.

Greater rhythm amplitude was associated with lower age acceleration measured by GrimAge and also with lower PhenoAge acceleration.

A higher relative amplitude — another measure of the contrast between active and inactive periods — was also associated with lower GrimAge acceleration.

3. Consistency from one day to the next was particularly important

People whose activity-rest rhythm remained more consistent from one day to another showed less age acceleration on both GrimAge and PhenoAge.

This day-to-day stability was also identified as one of the most influential rest-activity characteristics associated with epigenetic aging.

4. Fragmented and irregular rhythms showed the opposite pattern

Greater fragmentation of activity and rest across the day was associated with higher GrimAge acceleration.

Higher activity during the normally least active five-hour period was also associated with greater GrimAge acceleration.

Day-to-day variability in the timing of rest was another influential characteristic in the overall analysis.

Together, the results point toward strength, stability and regularity of the 24-hour rhythm as potentially relevant features of biological aging.

5. Not every epigenetic clock showed the same relationship

The strongest statistically significant findings were seen with GrimAge and PhenoAge.

Results for the two other clocks — Horvath and Hannum — generally pointed in the same direction but were not statistically significant.

The relationships involving the specific timing of daily rhythms were also more complex and varied with age.

This means the study does not support a simple message such as “earlier is better.” The organization and consistency of the 24-hour rhythm appear more informative than any single ideal time of day.

Longevity research often focuses on how much we exercise and how long we sleep.

This study introduces another potentially important dimension:

how consistently activity and rest are organized across the entire day.

The findings suggest that biological aging may be associated not only with the quantity of activity and sleep, but also with the strength, stability and regularity of our 24-hour rhythms.

This is biologically plausible. Circadian rhythms help coordinate sleep, metabolism, hormone secretion, cardiovascular function and many other physiological processes.

But the distinction between a marker and an intervention is important.

The study does not show that making your daily schedule more regular will reduce your epigenetic age.

To demonstrate that, researchers would need prospective and intervention studies showing that deliberately strengthening or stabilizing daily rhythms subsequently changes measures of biological aging.

For now, 24-hour rest-activity rhythms should therefore be considered promising markers associated with biological aging, rather than proven methods for slowing it.

This study adds an important dimension to the relationship between circadian biology and healthy aging.

The researchers were not studying sleep alone.

They examined how activity and rest are organized across the entire 24-hour cycle.

The most consistent pattern was that stronger and more stable rhythms were associated with a more favorable epigenetic-aging profile, while greater fragmentation and irregularity were associated with less favorable results.

But these findings require careful interpretation.

This was a cross-sectional observational study.

Rest-activity rhythms and epigenetic aging were assessed within the same study period. The study therefore cannot determine which came first.

Irregular rhythms could potentially contribute to biological aging. But the reverse is also possible: poorer health or more advanced biological aging could lead to weaker and more fragmented daily rhythms.

Other health, behavioral or environmental factors could influence both.

The study was also relatively small, with 207 participants, and participants came from one metropolitan area in Maryland. The long-running cohort may also represent a relatively healthy survivor population.

The results therefore need replication in larger and more diverse populations.