Your daily rhythm may be more important to your brain health than previously thought. Older adults with weaker, more disrupted activity patterns were far more likely to develop dementia than those with stable routines. A later daily energy peak was also associated with a higher risk. The study points to the internal clock as a possible early warning sign of cognitive decline.

Weaker Internal Clocks are Associated With Dementia Risk

A new study suggests that disruptions to the body’s internal clock may be associated with a higher risk of dementia. A study published in Neurology, the medical journal of the American Academy of Neurology, found that people with weaker and more irregular daily rhythms are more likely to develop dementia. The study also showed that individuals whose daily activity peaked later in the day were at higher risk than those whose activity peaked earlier. While these findings show a strong association, they do not prove that changes in circadian rhythm directly lead to dementia.

What Circadian Rhythms do in the Body

The circadian rhythm refers to the body’s natural timing system. It controls the 24-hour sleep-wake cycle and helps regulate important functions such as hormone release, digestion, and body temperature. This internal clock is controlled by the brain and responds to environmental signals, especially light.

When the circadian rhythm is strong, the body closely adapts to the daily cycle of light and darkness. This leads to consistent sleep and activity patterns, even when schedules or seasons change. In contrast, a weaker rhythm makes the internal clock more sensitive to disturbances. People with less stable rhythms are more likely to shift their sleep and activity times due to changes in their routine or daylight.

Aging, Circadian Changes, and Dementia

“As we age, changes in circadian rhythm occur, and there is evidence that circadian rhythm disturbances may be a risk factor for neurodegenerative diseases such as 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 that people with weaker and more fragmented rhythms, as well as people whose activity levels peaked later in the day, had an increased risk of dementia.”

The study followed 2,183 adults with an average age of 79 who did not have dementia at the start of the study. Among the participants, 24% were Black and 76% were White. Each participant wore a small heart monitor attached to their chest for an average of 12 days. These devices recorded periods of rest and activity, allowing researchers to analyze circadian rhythm patterns. The participants were then observed for about three years. During this time, 176 people were diagnosed with dementia.

Later Activity Peaks and Higher Risk

The scientists examined the data from the heart monitors using several indicators of circadian rhythm strength. One important measurement was relative amplitude, which reflects the difference between a person’s most active and least active times of day. A higher relative amplitude indicated a stronger and more clearly defined daily rhythm.

The participants were divided into three groups based on the strength of their rhythm. When comparing the strongest and weakest groups, 31 of the 728 people in the high-rhythm group developed dementia, compared to 106 of the 727 people in the low-rhythm group. After taking into account factors such as age, blood pressure, and heart disease, the researchers found that individuals in the group with the weakest rhythm had an almost two-and-a-half times higher risk of dementia. Each decrease in relative amplitude by one standard deviation was associated with a 54% increase in the risk of dementia.

The timing of daily activities also appeared to play a role. Individuals whose activity peaked in the late afternoon, at 2:15 p.m. or later, had a higher risk of dementia than those whose activity peaked earlier, between 1:11 p.m. and 2:14 p.m. About 7% of participants in the earlier activity peak group developed dementia, compared to 10% in the later activity peak group, representing a 45% higher risk. A later activity peak may indicate a discrepancy between the body’s internal clock and environmental cues such as daylight and darkness.

Why Disrupted Rhythms Could be Important

“Disruptions in the circadian rhythm can alter bodily processes such as inflammation and impair sleep, potentially increasing the amyloid plaques associated with dementia or reducing amyloid clearance from the brain,” Wang said.

Amyloid plaques are deposits of protein fragments in the brain. They consist mainly of the amyloid beta protein. These protein fragments clump together and are deposited between nerve cells. This can disrupt communication between nerve cells and trigger inflammation. Amyloid clearance refers to the removal or transport of amyloid proteins from the brain. This “cleansing” process is particularly active during sleep.

Future studies should investigate the potential role of circadian rhythm interventions, such as light therapy or lifestyle changes, to determine whether they can help reduce a person’s risk of dementia. One limitation of the study is that it does not include data on sleep disorders such as sleep apnea, which may have influenced the results.