Weaker Body Clocks Are Being Linked to a Higher Dementia Risk in Older Adults
Circadian rhythms, often described as the body’s internal clock, play a crucial role in regulating daily cycles such as sleep, activity, hormone release, digestion, and body temperature. A new large-scale study suggests that when these rhythms become weaker, more fragmented, or shift later in the day, the risk of developing dementia may rise significantly in older adults.
The study, published in the medical journal Neurology by researchers from the American Academy of Neurology, highlights a growing area of concern in aging and brain health. While the findings do not prove that disrupted body clocks directly cause dementia, they show a strong association that researchers believe deserves serious attention.
Understanding Circadian Rhythms and Why They Matter
Circadian rhythm is essentially the body’s natural 24-hour timing system, guided by the brain and strongly influenced by exposure to light and daily routines. When this system is functioning well, the body sends clear signals about when to be active, when to rest, and how to regulate internal processes.
People with strong circadian rhythms tend to have consistent sleep and activity patterns. Even when seasons change or schedules are disrupted, their internal clock remains relatively stable. On the other hand, people with weak circadian rhythms are more sensitive to changes in light exposure and daily routines. Their sleep and activity times may shift more easily, leading to irregular patterns.
As people age, changes in circadian rhythms are common. Previous research has already suggested that disruptions in these rhythms may be linked to neurodegenerative diseases, including dementia. This new study adds more detailed evidence to that growing body of research.
How the Study Was Conducted
The research followed 2,183 older adults who did not have dementia at the beginning of the study. The average age of participants was 79 years, making this a particularly relevant group for examining dementia risk. The study population included 24% Black participants and 76% white participants, providing some racial diversity in the sample.
To measure circadian rhythms accurately, participants wore small heart monitors attached to their chest. These devices recorded patterns of rest and activity continuously for an average of 12 days. Using this data, researchers were able to analyze how strong, regular, or fragmented each participant’s circadian rhythm was.
After this monitoring period, participants were followed for an average of three years. During that time, 176 people were diagnosed with dementia.
Measuring Circadian Rhythm Strength
Researchers focused on several indicators of circadian rhythm health, one of the most important being relative amplitude. Relative amplitude measures the difference between a person’s most active periods and least active periods during the day and night.
- High relative amplitude indicates a strong circadian rhythm, with clear distinctions between daytime activity and nighttime rest.
- Low relative amplitude suggests a weaker rhythm, where activity and rest patterns are less clearly defined.
Participants were divided into three groups based on their relative amplitude levels. When researchers compared outcomes, the differences were striking.
Among those with strong circadian rhythms, only 31 out of 728 people developed dementia. In contrast, 106 out of 727 people in the weakest rhythm group were diagnosed with dementia during the follow-up period.
After adjusting for factors such as age, blood pressure, and heart disease, researchers found that people with weaker circadian rhythms had nearly 2.5 times the risk of developing dementia compared to those with strong rhythms. Additionally, for every standard deviation decrease in relative amplitude, dementia risk increased by 54%.
The Importance of Activity Timing
The study also examined when participants reached their peak activity levels during the day. This turned out to be another important factor.
People whose activity levels peaked later in the afternoon, at 2:15 p.m. or later, were found to have a 45% higher risk of dementia compared to those whose activity peaked earlier, between 1:11 p.m. and 2:14 p.m.
In practical terms:
- About 7% of people in the earlier activity peak group developed dementia.
- Around 10% of those with later activity peaks were diagnosed with dementia.
A later peak in activity may indicate a misalignment between the body’s internal clock and environmental cues, such as daylight and darkness. This mismatch could have downstream effects on sleep quality and overall brain health.
Possible Biological Explanations
Although the study does not establish cause and effect, researchers have proposed several biological mechanisms that might explain the link between disrupted circadian rhythms and dementia risk.
One possibility involves inflammation. Disrupted body clocks may interfere with the body’s ability to regulate inflammatory processes, which are known to play a role in neurodegeneration.
Another key factor is sleep. Circadian rhythm disruptions often lead to poor or irregular sleep. During deep sleep, the brain helps clear amyloid proteins, which are closely associated with Alzheimer’s disease. If sleep is disrupted, amyloid clearance may be reduced, potentially accelerating cognitive decline.
Study Limitations to Keep in Mind
Like all research, this study has limitations. One important issue is that researchers did not have detailed information on sleep disorders, such as sleep apnea. These conditions can independently affect both circadian rhythms and dementia risk, meaning they could have influenced the results.
Additionally, because this is an observational study, it can only show associations, not direct causation. More research is needed to determine whether improving circadian rhythms can actually reduce dementia risk.
Why This Research Matters
Dementia is a growing global health challenge, especially as populations age. Identifying modifiable risk factors is critical. Circadian rhythm health may represent one such factor, as it is influenced by daily habits and environmental conditions.
Researchers suggest that future studies should explore whether circadian rhythm interventions could help lower dementia risk. Potential approaches include:
- Light therapy, especially exposure to bright light earlier in the day
- Lifestyle changes, such as maintaining consistent sleep and wake times
- Regular daily activity schedules, including exercise and social engagement
If proven effective, these strategies could offer relatively simple, low-cost ways to support brain health in older adults.
What We Already Know About Circadian Health
Beyond dementia, strong circadian rhythms are linked to better metabolic health, improved mood, stronger immune function, and better cardiovascular outcomes. Disruptions have been associated with depression, diabetes, and heart disease, further emphasizing the importance of maintaining a stable internal clock.
As research continues, circadian health is increasingly being viewed as a core pillar of healthy aging, alongside nutrition, physical activity, and mental stimulation.
Final Thoughts
This study adds important evidence to the idea that how our bodies keep time may be closely connected to brain health. While more research is needed to determine causation and effective interventions, the findings highlight circadian rhythm strength and timing as potential early indicators of dementia risk.
For older adults and caregivers, paying attention to daily routines, light exposure, and sleep consistency may become an increasingly important part of maintaining long-term cognitive health.
Research paper:
https://doi.org/10.1212/WNL.0000000000214513
