A new study has found that people with weaker or more irregular circadian rhythms—the body’s internal clock—may have a higher risk of developing dementia.
The research also showed that people whose activity levels peaked later in the day were more likely to develop dementia.
The study was published in the journal Neurology.
Circadian rhythm is the 24-hour cycle that controls when we sleep, wake up, eat, and carry out other body functions. It is guided by the brain and affected by things like sunlight and daily routines.
People with a strong circadian rhythm usually go to bed and wake up at the same time each day. They keep a regular pattern of rest and activity, even when their schedule changes. On the other hand, people with weaker rhythms are more affected by changes in light and daily routines. Their sleep and activity times shift more easily.
Dr. Wendy Wang, the study’s lead author from the University of Texas Southwestern Medical Center, explained that circadian rhythm changes are common as people age. Some research already suggests that such changes may increase the risk of brain diseases like dementia. Her team wanted to find out more.
The study included 2,183 people who were around 79 years old on average and did not have dementia at the start of the study. About a quarter of the participants were Black, and the rest were white.
Each person wore a small heart monitor on their chest for about 12 days to track their rest and activity. The data helped researchers measure the strength and pattern of each person’s circadian rhythm.
After about three years of follow-up, 176 people were diagnosed with dementia.
To measure rhythm strength, scientists looked at something called “relative amplitude”—the difference between the most active and least active parts of a day. A higher relative amplitude meant a stronger rhythm.
The participants were divided into three groups based on their rhythm strength. In the strongest rhythm group, 31 out of 728 people developed dementia. In the weakest rhythm group, 106 out of 727 people developed the disease.
After adjusting for health factors like age, blood pressure, and heart problems, the researchers found that people in the weakest rhythm group were nearly 2.5 times more likely to develop dementia than those in the strongest group. For every decrease in rhythm strength, the risk of dementia went up by 54%.
The researchers also looked at the time of day when people were most active. Those who peaked later in the afternoon—around 2:15 p.m. or later—had a 45% higher risk of dementia compared to those whose activity peaked earlier, between 1:11 p.m. and 2:14 p.m.
A late peak in activity may mean a person’s body clock is out of sync with natural signals like light and darkness. This misalignment might affect brain health by increasing inflammation or disrupting the brain’s ability to clear waste like amyloid plaques, which are linked to Alzheimer’s disease.
The study didn’t look at sleep disorders such as sleep apnea, which could also affect dementia risk, so more research is needed.
Still, the researchers believe this study shows that improving circadian rhythms through things like light therapy or better daily habits might help protect brain health.
If you care about dementia, please read studies about dietary strategies to ward off dementia, and how omega-3 fatty acids fuel your mind.
For more health information, please see recent studies about Choline deficiency linked to Alzheimer’s disease, and what to eat (and avoid) for dementia prevention.
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