A Disrupted Body Clock Is Linked to Higher Dementia Risk

A weakening body clock and later daily energy peaks may quietly raise dementia risk.

• A new study suggests the body’s internal clock, known as circadian rhythm, may play an important role in a person’s risk of developing dementia.
• More than 2,000 older adults wore small monitors for about 12 days, allowing researchers to track daily patterns of rest and activity.
• The results showed that people with weaker or more disrupted body clocks were more likely to develop dementia over time.
• Participants whose activity levels peaked later in the day, rather than earlier, faced a 45% higher risk of dementia.
• Researchers say future studies testing circadian rhythm strategies, such as light exposure or lifestyle changes, could reveal ways to reduce dementia risk.

Weaker Daily Rhythms Tied to Dementia Risk

A new study suggests that disruptions in the body’s internal timing system may be linked 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 activity patterns peaking later in the day, rather than earlier, were associated with increased risk. These findings point to a connection but do not show that circadian rhythm changes directly cause dementia.

How the Body’s Internal Clock Works

Circadian rhythm is often described as the body’s internal clock. It helps control the 24-hour sleep-wake cycle and influences many essential functions, including hormone release, digestion, and body temperature. This timing system is regulated by the brain and shaped by exposure to light.

When circadian rhythms are strong, the body stays closely aligned with the natural day-night cycle. People with stable rhythms usually keep consistent sleep and activity schedules, even when routines or seasons change. Weaker rhythms are more easily disrupted by changes in light or daily schedules, leading to shifts in sleep and activity patterns throughout the year.

Aging, Rhythm Changes, and Brain Health

“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 Was Included in the Study

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

To track daily rhythms, participants wore small heart monitors attached to the chest for an average of 12 days. These devices recorded periods of rest and activity. Researchers then followed participants for about three years, during which 176 people were diagnosed with dementia.

Measuring Circadian Rhythm Strength

Researchers analyzed the monitor data using several indicators of circadian rhythm strength. One key measure was relative amplitude, which reflects the gap between a person’s most active and least active periods during the day. Higher relative amplitude indicated a clearer and stronger daily rhythm.

Participants were grouped into three categories based on rhythm strength. Among those with the strongest rhythms, 31 of 728 people developed dementia. In contrast, 106 of the 727 people in the weakest rhythm group were diagnosed with the condition. After accounting for factors such as age, blood pressure, and heart disease, researchers found that people in the weakest 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 Increased Risk

The timing of daily activity also appeared to play a role. People whose activity peaked later in the afternoon, at 2:15 p.m. or later, faced a higher risk of dementia than those who peaked earlier, between 1:11 p.m. and 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 indicate a mismatch between the body’s internal clock and environmental signals such as daylight and darkness.

Why Disrupted Rhythms May 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 study is that researchers did not have information on sleep disorders, such as sleep apnea, which could have influenced the results.

Reference: “Association Between Circadian Rest-Activity Rhythms and Incident Dementia in Older AdultsThe Atherosclerosis Risk in Communities Study” by Wendy Wang, Amal A. Wanigatunga, Lacey H. Etzkorn, Jill A. Rabinowitz, Priya Palta, James Russell Pike, Ryan J. Dougherty, Vadim Zipunnikov, Francesca R. Marino, Ciprian Crainiceanu, Adam P. Spira, Jennifer Schrack and Lin Y. Chen, 29 December 2025, Neurology.
DOI: 10.1212/WNL.0000000000214513

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