Dementia is a growing health concern around the world, especially as populations age. It affects memory, thinking, behavior, and the ability to carry out everyday activities.
While age remains the strongest risk factor, scientists are increasingly interested in other biological changes that may raise the risk of developing dementia.
A new study suggests that the strength and timing of the body’s internal clock may play an important role.
Research published on December 29, 2025, in the journal Neurology, found that people with weaker and more irregular body clocks were more likely to develop dementia over time. The study also showed that people whose daily activity peaked later in the day faced a higher risk than those whose activity peaked earlier.
While the findings do not prove that changes in the body clock cause dementia, they reveal a strong connection that may help explain why some people are more vulnerable than others.
The body’s internal clock, known as the circadian rhythm, helps control the natural 24-hour cycle of sleep and wakefulness. It also influences many essential processes, including hormone release, digestion, body temperature, and energy levels.
This internal timing system is guided by the brain and responds mainly to light and darkness. When the body clock is working well, people tend to feel alert during the day and sleepy at night, with stable and predictable patterns of rest and activity.
Strong circadian rhythms help the body stay in sync with the natural day-night cycle, even when daily routines change slightly.
In contrast, weaker rhythms are more easily disrupted. People with less stable rhythms may experience irregular sleep patterns, shifts in activity times, and difficulty adjusting to changes in schedule or daylight. These disruptions tend to become more common with aging.
The study’s lead author, Wendy Wang, explained that changes in circadian rhythms are a normal part of aging, but growing evidence suggests that these changes may also be linked to brain diseases such as dementia.
The researchers wanted to understand whether weaker or more fragmented daily rhythms could help predict who is more likely to develop dementia later on.
To explore this question, the researchers followed 2,183 older adults with an average age of 79. None of the participants had dementia at the start of the study. The group included both Black and white participants, allowing researchers to observe patterns across different backgrounds.
Each person wore a small heart monitor attached to the chest for about 12 days. These devices recorded periods of rest and activity, giving scientists detailed information about each person’s daily rhythm.
After the monitoring period, participants were followed for roughly three years. During that time, 176 people were diagnosed with dementia. The researchers then compared the rhythm patterns of those who developed dementia with those who did not.
One of the key measures used in the study was called relative amplitude. This measure reflects how clearly a person’s day is divided between active and restful periods.
A higher relative amplitude means a stronger rhythm, with clear differences between the most active and least active times of day. A lower relative amplitude means a weaker rhythm, with more overlap between activity and rest.
Participants were divided into three groups based on rhythm strength. Among those with the strongest rhythms, only 31 out of 728 developed dementia. In contrast, 106 out of 727 people in the weakest rhythm group developed dementia.
After accounting for other factors such as age, blood pressure, and heart disease, researchers found that people with the weakest rhythms had nearly two and a half times the risk of developing dementia. Each noticeable drop in rhythm strength was linked to a significant increase in risk.
The timing of daily activity also appeared to matter. People whose activity levels peaked later in the afternoon faced a higher risk of dementia than those whose activity peaked earlier. About 7 percent of people with earlier activity peaks developed dementia, compared to about 10 percent of those with later peaks. This difference translated to a 45 percent higher risk.
A later activity peak may reflect a mismatch between the body’s internal clock and environmental signals such as daylight and darkness. When the internal clock is out of sync, important biological processes may no longer happen at the most effective times.
Researchers believe that disrupted circadian rhythms may affect the brain in several ways. Poor rhythm regulation may increase inflammation, interfere with sleep quality, and disrupt how the brain clears harmful proteins. These proteins can build up in the brain and are commonly linked to dementia.
The researchers noted that future studies should explore whether improving circadian rhythms could help lower dementia risk. Possible approaches include light therapy, regular sleep schedules, physical activity earlier in the day, and other lifestyle changes designed to strengthen the body clock.
The study does have limitations. For example, it did not include detailed information about sleep disorders such as sleep apnea, which could influence both circadian rhythms and dementia risk. Even so, the findings add to growing evidence that the body clock plays an important role in brain health.
Overall, the study suggests that maintaining a strong and well-timed daily rhythm may be important not just for sleep and energy, but also for long-term brain health. While more research is needed, paying attention to daily routines, light exposure, and activity timing could one day become part of strategies to reduce dementia risk.
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