A weak body clock may be an early warning for dementia

• A large new study suggests the body's internal clock, known as circadian rhythm, may play an important role in dementia risk.
• More than 2,000 older adults wore small monitors for about 12 days, allowing researchers to closely track daily patterns of rest and activity.
• People whose body clocks were weaker or more irregular were significantly more likely to develop dementia over the following years.
• Those whose activity levels peaked later in the day, rather than earlier, showed a 45% higher risk of dementia.
• Researchers say future studies exploring circadian rhythm approaches such as light exposure or lifestyle changes could reveal new ways to reduce dementia risk.

Weaker Body Clocks Linked to Dementia Risk

A new study suggests that disruptions in the body's internal clock may be tied to a higher risk of dementia. Research published on December 29, 2025, in Neurology, the medical journal of the American Academy of Neurology, found that people with weaker and more irregular circadian rhythms were more likely to develop dementia. The study also showed that individuals whose daily activity levels peaked later in the day faced a higher risk than those who peaked earlier. While these findings reveal a strong link, they do not show that circadian rhythm changes directly cause dementia.

What Circadian Rhythms Do in the Body

Circadian rhythm refers to the body's natural timing system. It controls the 24-hour sleep-wake cycle and helps regulate key functions such as hormone release, digestion, and body temperature. This internal clock is directed by the brain and responds to environmental signals, especially light.

When circadian rhythms are strong, the body stays closely aligned with the daily cycle of light and dark. This leads to consistent patterns of sleep and activity, even when schedules or seasons change. In contrast, weaker rhythms make the body clock more sensitive to disruptions. People with less stable rhythms are more likely to shift their sleep and activity times due to changes in routine or daylight.

Aging, Circadian Changes, and Dementia

"Changes in circadian rhythms happen with aging, and evidence suggests that circadian rhythm disturbances may be a risk factor for neurodegenerative diseases like dementia," said study author Wendy Wang, MPH, PhD, of the Peter O'Donnell Jr. School of Public Health at UT Southwestern Medical Center in Dallas, Texas. "Our study measured these rest-activity rhythms and found people with weaker and more fragmented rhythms, and people with activity levels that peaked later in the day, had an elevated risk of dementia."

Who Took Part in the Study

The research followed 2,183 adults with an average age of 79 who did not have dementia when the study began. Among the participants, 24% were Black people and 76% were white people.

Each participant wore a small heart monitor attached to the chest for an average of 12 days. These devices tracked periods of rest and activity, allowing researchers to analyze circadian rhythm patterns. Participants were then monitored for about three years. During that time, 176 people were diagnosed with dementia.

How Researchers Measured Rhythm Strength

Scientists examined the heart monitor data using several indicators of circadian rhythm strength. One key measure was relative amplitude, which reflects the difference between a person's most active and least active times of day. Higher relative amplitude indicated a stronger and more clearly defined daily rhythm.

Participants were divided into three groups based on rhythm strength. When comparing the strongest and weakest groups, 31 of the 728 people in the high rhythm group developed dementia, while 106 of the 727 people in the low rhythm group did. After accounting for factors such as age, blood pressure, and heart disease, researchers found that those in the weakest rhythm group had nearly two and a half times the risk of dementia. Each standard deviation drop in relative amplitude was linked to a 54% increase in dementia risk.

Later Activity Peaks and Higher Risk

The timing of daily activity also appeared to matter. People whose activity peaked later in the afternoon, at 2:15 p.m. or later, had a higher risk of dementia than those whose activity peaked earlier, between 1:11 p.m.-2:14 p.m. About 7% of participants in the earlier peak group developed dementia, compared with 10% in the later peak group, representing a 45% higher risk.

A later activity peak may reflect a mismatch between the body's internal clock and environmental signals such as daylight and darkness.

Why Disrupted Rhythms Might Matter

"Disruptions in circadian rhythms may alter body processes like inflammation, and may interfere with sleep, possibly increasing amyloid plaques linked to dementia, or reducing amyloid clearance from the brain," said Wang. "Future studies should examine the potential role of circadian rhythm interventions, such as light therapy or lifestyle changes, to determine if they may help lower a person's risk of dementia."

Study Limitations

One limitation of the research is that it did not include data on sleep disorders, such as sleep apnea, which could have influenced the results.