Circadian rhythms that are less consistent and more fragmented may be associated with a higher risk of developing dementia, according to a recent study published in Neurology, the journal of the American Academy of Neurology. The research, released on December 29, 2025, found that individuals whose circadian activity peaked later in the day also faced increased dementia risk. However, the authors note that these findings show an association rather than a direct cause.
Circadian rhythm refers to the body's internal clock that regulates sleep-wake cycles and other bodily processes such as hormone levels, digestion, and body temperature. This internal timing is influenced by signals from the brain and environmental factors like light exposure.
A strong circadian rhythm helps synchronize body functions with the 24-hour day, maintaining regular patterns for sleep and activity even when schedules or seasons change. In contrast, weaker circadian rhythms make individuals more susceptible to disruptions caused by changes in light or daily routines.
"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."
The research followed 2,183 participants with an average age of 79 who did not have dementia at baseline; 24% were Black participants and 76% were white participants. Each wore a small heart monitor adhered to their chest for about 12 days to record rest-activity cycles. Data collected was used to analyze circadian rhythm strength and patterning over time.
Participants were monitored for an average follow-up period of three years during which 176 developed dementia. Researchers assessed several measures related to circadian strength including relative amplitude—the difference between periods of highest and lowest activity within each individual’s cycle—with higher values indicating stronger rhythms.
Comparisons showed that those in the lowest third for relative amplitude had nearly two-and-a-half times greater risk of developing dementia than those in the highest group. For every standard deviation decrease in this measure, there was a corresponding 54% increase in dementia risk.
In addition to rhythm strength, researchers observed timing differences: people whose peak daily activity occurred at or after 2:15 p.m. had a 45% higher likelihood of being diagnosed with dementia compared to those peaking earlier (between 1:11 p.m. and 2:14 p.m.). In percentage terms, seven percent of early-peak individuals developed dementia versus ten percent among late-peakers.
Having a later peak may indicate misalignment between biological clocks and environmental cues such as daylight hours.
"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."
The authors acknowledged limitations including lack of data on certain sleep disorders like sleep apnea which might have influenced results.
