The study included 207 middle-aged and older adults participating in the long-running Baltimore Epidemiologic Catchment Area (ECA) cohort study. Participants had an average chronological age of around 68 years.

To measure daily activity patterns, the research team, led by the Johns Hopkins Bloomberg School of Public Health, used wrist-worn actigraphy devices for approximately 7 consecutive days.

These devices tracked periods of activity, rest, sleep, and sedentary behavior. Participants also kept sleep and nap logs.

The investigators compared these activity patterns with 4 established epigenetic clocks that estimate biological age using epigenetic markers. The clocks used in the study were:

• Horvath clock
• Hannum clock
• PhenoAge
• GrimAge.

The findings suggest that individuals with stronger and less fragmented rest-activity rhythms had significantly lower biological age scores on the GrimAge and PhenoAge measures, indicating slower physiological aging.

The associations remained even after accounting for factors such as chronological age, sex, education level, and certain health conditions.

Co-senior author Brion Maher, PhD, MS, a professor in the Bloomberg School’s Department of Mental Health was not surprised by the strength of the associations.

He told Medical News Today “it is not entirely surprising since GrimAge and PhenoAge are newer-generation epigenetic clocks that were designed to capture aging-related health risks, including mortality risk, disease burden, and physiological decline.”

“Because rest-activity rhythms are closely related to overall health, it makes sense that their associations would be more apparent in epigenetic clocks that are associated with health and mortality than with clocks that are primarily designed to estimate chronological age.”

– Brion Maher, PhD, MS

Similar trends also appeared with the Horvath and Hannum clocks. However, those findings did not reach statistical significance.

Rest-activity rhythms reflect the body’s broader circadian system. This describes the internal biological processes that regulate sleep, activity, hormone release, metabolism, and other functions over a roughly 24-hour cycle.

As people age, these rhythms often weaken and become more irregular. Another recent study by the research team linked weaker and more fragmented rest-activity rhythms to shrinking of the brain in older adults.

Previous studies have also linked disrupted circadian rhythms with a range of health problems, including cognitive decline, psychiatric disorders, and some cancers.

Therefore, the researchers suggest that rest-activity rhythms could become a useful marker of aging, and may provide a more meaningful measure of health than chronological age alone. If supported by further research, they may also emerge as possible targets for interventions to slow the aging process.

The study’s lead author was Chunyu Liu, a PhD student supervised by Maher and the other co-senior author, Adam Spira, PhD, MA, also a professor in the Bloomberg School’s Department of Mental Health.

“I think rest-activity rhythms may be an observable window into circadian regulation, and circadian regulation is not just related to aging—it may be part of the aging process itself,” Liu told MNT.

“In addition, circadian regulation is closely connected with many biological processes involved in aging. Stronger circadian rhythmicity may help coordinate these processes, which could be reflected in lower epigenetic age acceleration.”
– Chunyu Liu

Spira explained to MNT how measuring wrist movement in the study may reflect fragmented rhythms.

“In this study, we did not directly measure circadian rhythms — we measured movement at the wrist over 24-hour periods, which is an indirect measure of circadian function. The resulting data also reflect an array of environmental influences, such as bright light exposure at certain times of day,” he detailed.

“Fragmented rhythms represent more frequent, rapid transitions between rest and activity within a day. Fragmented sleep could manifest as fragmented motor activity at night in these rest-activity rhythm metrics,” Spira added.

“In general, more continuous, consolidated sleep is thought to be one of the many consequences or manifestations of stronger, less fragmented circadian rhythms,” he told us.

While the study highlights a clear distinction between daytime activity and nighttime rest and “younger” biological aging, the authors emphasize that the study was cross-sectional, meaning it examined activity rhythms and biological aging at roughly the same point in time.

As a result, the research cannot determine whether disrupted rhythms contribute to faster aging, or whether aging itself weakens circadian patterns. The researchers note that longer-term studies will be necessary to clarify the direction of the relationship.

They also add that the study population may have underestimated the true effect, as the participants were older adults healthy enough to take part, whereas those who experience more rapid aging may have been too unwell to participate.

The researchers suggest that wearable technology could eventually help monitor physiological aging and other health risks in real time.

“I think this is feasible in the long term,” Liu said to MNT. “Wearable devices are very good at continuously capturing patterns of rest and activity over multiple days or weeks. Those data likely provide a more reliable picture of daily rhythms than the information a healthcare provider obtains from a patient during a short clinical visit.”

“However, physiological aging is complex and likely cannot currently be measured directly in real time by wearables alone,” she added.