A growing body of research suggests that dementia risk is influenced not only by genetics and cardiovascular health, but also by how well the body keeps time. Now, a large prospective study published in Neurology provides some of the strongest evidence yet that disruptions to circadian rhythms, the body’s internal clock, are associated with a substantially higher risk of developing dementia in older adults.
“Changes in circadian rhythms happen with aging, and evidence suggests that circadian rhythm disturbances may be a risk factor for neurodegenerative diseases like dementia,” explained study author Wendy Wang, PhD, MPH, of the Peter O’Donnell Jr. School of Public Health at UT Southwestern Medical Center in Dallas, Texas.
The findings come from the Atherosclerosis Risk in Communities (ARIC) study, which followed more than 2,000 dementia-free adults with an average age of 79, using wearable monitors to track daily patterns of rest and activity. Over a median follow-up of three years, participants with weaker or more irregular circadian rhythms were significantly more likely to be diagnosed with dementia.
Measuring the body clock in real life
Rather than relying on self-reported sleep or activity patterns, researchers used accelerometer data collected from a chest-based ambulatory ECG patch worn continuously for about 12 days. These data allowed the team to quantify circadian rhythm strength, regularity, and timing in daily life.
One key measure was “relative amplitude,” which captures how distinct a person’s most active and least active periods are across a 24-hour cycle. Lower relative amplitude indicates a weaker circadian rhythm, with less separation between day and night activity.
Participants in the weakest rhythm group had nearly 2.5 times the risk of developing dementia compared with those whose rhythms were strongest, even after adjusting for age, cardiovascular risk factors, education, and genetic risk such as APOE ε4 status. Each standard-deviation decrease in rhythm strength translated into a 54% higher dementia risk.
Why timing matters, not just sleep
The study also found that when people were most active mattered. Individuals whose daily activity peaked later in the afternoon, after about 2:15 p.m., had a 45% higher risk of dementia compared with those whose activity peaked earlier.
This delayed timing, known as a later “acrophase,” may reflect misalignment between the body clock and environmental cues such as daylight. Such misalignment has been linked in previous studies to inflammation, metabolic disruption, and impaired clearance of amyloid-β from the brain.
The associations were observed in a racially diverse population, including both Black and White participants—an advance over earlier studies that were often limited to more homogeneous groups.
From population risk to precision prevention
The study does not prove that circadian disruption causes dementia, but it strengthens the case that circadian rhythms are a meaningful and potentially modifiable risk factor. From a precision-medicine perspective, the implications are significant.
Wearable devices capable of passively capturing circadian patterns are already widely used in clinical practice for cardiac monitoring. This raises the possibility that circadian rhythm metrics could one day be incorporated into individualized dementia risk assessments, alongside genetics, vascular health, and cognitive testing.
The findings also point toward targeted interventions. Light therapy, structured sleep and activity schedules, time-restricted eating, and other chronotherapy approaches are already under investigation for metabolic and mood disorders. This study provides a strong rationale to test whether similar strategies could help preserve cognitive health—especially in people showing early circadian disruption.
A new window into early dementia risk
Because dementia has a long preclinical phase, identifying early, actionable risk signals is a major goal of preventive neurology. By showing that everyday activity rhythms captured by a simple wearable device predict future dementia risk, this research moves circadian biology from an abstract concept into a measurable clinical domain.
As researchers continue to explore how sleep, light exposure, and daily routines interact with brain aging, the message is becoming clearer: keeping a strong, well-timed body clock may be an important part of protecting the brain over the long term.
