A recent large-scale study has indicated that disruptions in the body's internal clock, or circadian rhythm, may be associated with a higher risk of developing dementia. The research, published in the journal Neurology on December 29, 2025, involved over 2,000 older adults who wore heart monitors for approximately 12 days, allowing researchers to closely monitor their daily patterns of activity and rest.

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The study found that individuals with weaker or more fragmented circadian rhythms faced a significantly elevated risk of dementia over the years following the study. Specifically, those whose activity levels peaked later in the day were observed to have a 45% higher risk of developing dementia compared to individuals whose activity levels peaked earlier.

Circadian rhythm is essential as it regulates the 24-hour sleep-wake cycle and influences various bodily functions, including hormone release and digestion. A well-aligned circadian rhythm typically correlates with consistent sleep and activity patterns. However, disruptions in this internal clock may lead to irregular sleep and activity times, potentially increasing the risk for neurodegenerative diseases like dementia.

Wendy Wang, MPH, PhD, a lead author from the Peter O'Donnell Jr. School of Public Health at UT Southwestern Medical Center, stated that with aging, circadian rhythm disturbances can emerge, which may be risk factors for dementia. The study tracked 2,183 adults, aged around 79, who did not have dementia at the onset of the research, with a diverse participant group comprising 24% Black individuals and 76% white individuals.

Participants were monitored for about three years, during which 176 were diagnosed with dementia. The researchers analyzed the heart monitor data using various indicators of circadian rhythm strength, with relative amplitude being a key measure. A higher relative amplitude indicated a stronger, more defined daily rhythm.

Participants were categorized into three groups based on their rhythm strength. Comparing the strongest and weakest groups revealed that 31 of the 728 individuals in the high rhythm group developed dementia, while 106 of the 727 from the low rhythm group did. After adjustments for factors such as age and heart disease, those in the weakest rhythm group exhibited nearly 2.5 times the dementia risk, with each standard deviation decrease in relative amplitude correlating to a 54% increase in risk.

The timing of daily activity also proved significant; those whose activity peaked later, particularly after 2:15 p.m., had a greater risk of dementia than those peaking earlier. About 7% of participants in the earlier peak group were diagnosed with dementia, compared to 10% in the later peak group.

Wang noted that disturbances in circadian rhythms could disrupt bodily processes, potentially affecting inflammation and sleep patterns and facilitating the buildup of amyloid plaques associated with dementia.

The study's limitations included the absence of data on sleep disorders, such as sleep apnea, which might have affected the outcomes.