- Circadian rhythm refers to the changes that occur in organisms over a 24-hour period.
- Rest and activity patterns throughout the day are one way to explore components of circadian rhythm.
- One study found that more fragmented and weaker circadian rest activity rhythms and having peak activity time later in the day were linked to an increased risk for dementia.
Circadian rhythms describe the body’s natural, roughly 24-hour internal clock. They regulate changes that occur throughout the day and can impact aspects like sleep, waking, and appetite.
A recent study explored rest and activity rhythms (RARs), which “are behavioral markers of circadian rhythms,” and how they relate to risk for dementia.
The study was published in Neurology, which is the medical journal of the American Academy of Neurology. The findings suggest that people with disrupted RARs may have a higher risk of dementia.
For this study, researchers specifically focused on RARs, which refer to patterns in people’s rest and activity throughout the day. They wanted to see how these related to incident dementia. This describes the development of new cases of dementia within a population over a specific time.
All participants wore ambulatory cardiac patches that monitored heart electrical activity for at least 3 days. The average time participants wore the monitoring patch was 12 days. This enabled them to evaluate the RARs of the participants.
They adjusted for various factors in three distinct models and also did sensitivity analyses. The average age of participants was 79 years, the median follow-up time was 3.3 years, and 8% of participants developed dementia.
Weaker rhythm strength was associated with an increased risk for dementia, with each standard deviation decrease in rhythm strength linked to a 54% greater risk for dementia.
Each standard deviation increase in within-day rhythm fragmentation was linked to a 19% higher risk for dementia. Those with more fragmented rhythms experience symptoms like daytime sleepiness or waking up in the middle of the night.
Researchers observed a U-shaped pattern for day-to-day consistency of rhythm and dementia, but did not find a significant association between these two components.
Other evaluations of rhythm strength were also linked to a greater risk for dementia. Those with the lowest rhythm strength were at a higher risk for dementia compared to those with the highest rhythm strength.
Researchers also found a significant interaction for race “when assessing the association between interdaily stability and dementia.”
However, researchers advise caution regarding this finding, which evaluates day-to-day rhythm consistency and highlights the need for more research in this area.
The related editorial notes that the findings suggest lower day-to-day rhythm consistency is associated with greater dementia risk for Black individuals but not white individuals.
Sensitivity analyses revealed participants with the lowest rhythm strength had the highest risk for dementia compared to those with the highest rhythm strength.
Additionally, a later peak time activity, such as being most active later in the day, was associated with a 69% higher risk for dementia compared to people with normal peak time activity.
The researchers also found that most factors were still associated with an increased risk for dementia after excluding participants with mild cognitive impairment.
They note that “overall, results indicate that alterations in circadian RARs, specifically weaker rhythm strength, more fragmented rhythm, and later peak activity time, may be risk factors of incident dementia.”
Dung Trinh, MD, internist, of MemorialCare Medical Group in Irvine, CA, and Chief Medical Officer of Healthy Brain Clinic, who was not involved in this research, commented the following about the study:
“This study provides strong and timely evidence that disruptions in circadian RARs are prospectively associated with an increased risk of developing dementia in older adults…While the study cannot establish causality and does not distinguish dementia subtypes, it meaningfully advances our understanding of how circadian biology may relate to brain health in aging.”
Since this study only included white and Black individuals, the results might not be generalizable to other groups. Since it focused on older adults, it is unclear if the results are applicable to middle-aged adults.
The research also did not differentiate between dementia types because they did not have this data. They also did not have objective measures for sleep disorders.
Giulio Taglialatela, PhD, Vice President, Brain Health, Director, Moody Brain Health Institute, Lawrence J. Del Papa Distinguished Chair in Neurodegenerative Disease Research, and Professor in the Department of Neurology, likewise not involved in this research, noted that:
“The study did not include direct assessment of sleep patterns or sleep disturbances. Because disrupted or irregular sleep has been associated with increased amyloid production and reduced amyloid clearance, having parallel objective sleep data would have strengthened the conclusions.”
It may not be possible to directly compare certain results to other studies because participants wore the monitor patch on their chests, and in other studies, it was worn on the hip or wrist.
Researchers’ inclusion and exclusion criteria for the analysis could also limit the findings. For example, they chose to exclude Black participants from two county sites because of a low number of these participants in these areas.
They also chose to include individuals with mild cognitive impairment in the main analysis. The measurements of RARs also have drawbacks, such as certain approximations, assumptions, and estimations.
Finally, researchers note that reverse causality is still a possibility. It is also possible that researchers also missed data, such as undiagnosed dementia cases, and some covariate data was from participant reporting.
The research was supported by several grants and federal funding, and two authors noted possible conflicts of interest.
The editorial further notes that the devices used by participants have “not been fully validated for circadian assessment.”
It also notes that researchers did not directly assess and adjust for participants’ physical activity, so the associations could reflect decreased activity from other factors like depression.
Future research can continue to explore the relationship between circadian rhythms and dementia and how they may influence each other. Researchers note the possibility of a bidirectional relationship. Future research can also explore how certain interventions, like light therapy, affect dementia risk.
The researchers suggest that wearable devices for monitoring heart rhythm could help identify those at higher risk for dementia.
Taglialatela noted the following as well:
“Another translational strength is the use of accelerometer data derived from wearable ambulatory ECG monitors. These monitors are already widely utilized in clinical practice for cardiac assessment, and this study suggests they may provide dual value by also generating movement information relevant to dementia prediction. ”
The results also indicate that addressing abnormalities in RARS could impact risk for dementia, though more research is necessary.
“In the longer term, this work supports growing interest in circadian-focused interventions—such as light therapy, structured sleep and activity schedules, and other lifestyle modifications—as possible strategies to promote brain health and reduce dementia risk,” Trinh noted.
“However, additional studies are needed to determine whether improving circadian rhythms can directly alter dementia trajectories and to clarify how these measures might be incorporated into routine clinical care,” he added.
