Older adults with weaker or more irregular daily rest-activity rhythms were more likely to be diagnosed with dementia over about three years, according to a study published in *Neurology*. The research also linked later-afternoon activity peaks to higher dementia risk, though it did not establish that disrupted circadian rhythms cause dementia.
A study published on December 29, 2025, in Neurology—the medical journal of the American Academy of Neurology—reported an association between circadian rest-activity rhythms and later dementia diagnoses.
Circadian rhythm refers to the body’s internal 24-hour timing system that helps regulate the sleep-wake cycle and other functions such as hormone release, digestion and body temperature. The system is strongly influenced by environmental cues, especially light.
Study design and participants
Researchers followed 2,183 adults with an average age of 79 who did not have dementia at the start of the study. Of the participants, 24% were Black and 76% were white. To measure daily patterns of rest and activity, participants wore a small heart monitor attached to the chest for an average of 12 days.
Participants were then followed for an average of about three years. During follow-up, 176 people were diagnosed with dementia.
Rhythm strength and dementia risk
Using data from the monitors, the researchers evaluated several indicators of rhythm strength, including relative amplitude, a measure of the difference between a person’s most active and least active periods. Higher relative amplitude indicated a stronger, more clearly defined daily rhythm.
Participants were divided into three groups by rhythm strength. In the strongest rhythm group (728 people), 31 developed dementia. In the weakest rhythm group (727 people), 106 developed dementia. After adjusting for factors including age, blood pressure and heart disease, the researchers reported that the weakest group had nearly 2.5 times the risk of dementia compared with the strongest group. They also reported that each standard-deviation decrease in relative amplitude was associated with a 54% higher dementia risk.
Later activity peaks also linked to higher risk
The study also found an association between the timing of a person’s daily activity peak and dementia risk. People whose activity peaked at 2:15 p.m. or later had a 45% higher risk of dementia than those whose activity peaked between 1:11 p.m. and 2:14 p.m. In the earlier-peak group, about 7% developed dementia, compared with about 10% in the later-peak group.
Expert comment and limitations
“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. “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.”
Wang added that disrupted circadian rhythms may affect processes such as inflammation and sleep, and could influence amyloid-related brain changes linked to dementia—mechanisms that require further study.
The researchers cautioned that the findings show an association and do not prove that circadian rhythm disruption causes dementia. They also noted a limitation: the study did not include data on sleep disorders such as sleep apnea, which could affect rest-activity patterns. Future research, the authors said, should test whether interventions—including light therapy or lifestyle changes—can reduce dementia risk.
