Research has shown that individuals with weak or fragmented circadian rhythms may have a higher risk of dementia. In particular, a correlation was observed between a peak activity time later than 2 PM and an increased risk of dementia. However, it is important to interpret this study with caution as it shows correlation rather than causation.
The circadian rhythm is our body's biological clock, regulating various physiological processes including the 24-hour sleep-wake cycle, hormone secretion, digestion, and temperature control. This rhythm is controlled by the brain, with light exposure acting as a key signal. A strong circadian rhythm means that the cycles of activity and rest are distinct, allowing sleep and activity times to remain relatively consistent despite seasonal or schedule changes. Conversely, a weak rhythm can easily be disrupted by changes in light or lifestyle patterns.
Weak Circadian Rhythm Linked to Increased Dementia Risk
A research team from UT Southwestern Medical Center in the United States conducted a study involving 2,183 elderly participants with an average age of 79 who had no dementia at the start of the study. Participants wore small heart monitors attached to their chests to record their rest and activity patterns for an average of 12 days, and the researchers subsequently tracked them for about three years. During this period, a total of 176 participants were diagnosed with dementia.
The researchers analyzed several indicators to assess the strength of the circadian rhythm, using relative amplitude as a key indicator. Relative amplitude refers to the difference between the most active time of day and the least active time, with a larger value indicating a stronger circadian rhythm.
In other words, a strong circadian rhythm indicates a clear pattern of high activity during the day and rest at night, meaning the biological clock is well-aligned with the 24-hour cycle. Conversely, a weak circadian rhythm means that the boundaries between activity and rest are blurred, leading to an inconsistent sleep-wake rhythm that is easily disrupted by external environments.
When comparing three groups of participants, 31 individuals in the group with the strongest rhythm (728 people) were diagnosed with dementia, while 106 individuals in the group with the weakest rhythm (727 people) received a diagnosis. Even after adjusting for factors that could influence the results, such as age, blood pressure, and heart disease, the dementia risk in the weak rhythm group was found to be approximately 2.5 times higher. For every one standard deviation decrease in relative amplitude, the risk of dementia increased by 54%.
Later Peak Activity Time Also Increases Risk
When individuals are most active during the day is also an important indicator. Compared to those whose peak activity time is between 1:11 PM and 2:14 PM, individuals whose peak occurs after 2:15 PM had a 45% higher risk of dementia.
In fact, among the group that was most active early in the day, 7% were diagnosed with dementia, while 10% of the late group received a diagnosis. The researchers analyzed that a later peak activity time suggests a potential mismatch between the biological clock and environmental signals such as light and darkness.
Dr. Wendy Wang, the lead author of the study, stated, "Circadian rhythm disruption may alter bodily processes such as inflammatory responses and disrupt sleep, potentially increasing the accumulation of amyloid plaques associated with dementia or reducing their removal. Future research needs to verify whether interventions to enhance circadian rhythms, such as light therapy or lifestyle adjustments, can lower dementia risk."
Meanwhile, the research team noted that a limitation of this study was the insufficient information on sleep disorders such as sleep apnea.
The results of this study were published in the recent issue of the American Academy of Neurology's journal 《Neurology》 under the title 'Association Between Circadian Rest-Activity Rhythms and Incident Dementia in Older Adults.'
[Frequently Asked Questions]
Q1. What does it mean to have a weak circadian rhythm?
A. It refers to a state where the distinction between activity and rest during the day is not clear, and sleep-wake times are inconsistent. It is characterized by being easily disrupted by light exposure or changes in daily schedules.
Q2. Does being more active in the afternoon directly cause dementia?
A. No. This study is an observational study that shows a correlation between having a later peak activity time or a weak circadian rhythm pattern and an increased risk of dementia, rather than proving causation.
Q3. Can improving the biological clock lower the risk of dementia?
A. There is no definitive conclusion yet. However, the researchers suggested that interventions that strengthen circadian rhythms, such as light therapy and regular lifestyle habits, may be helpful and emphasized the need for further research.
