- A person’s circadian rhythm plays an important role in their overall health.
- Past research shows that an unhealthy circadian rhythm may increase a person’s risk for several health conditions, including dementia, such as Alzheimer’s disease.
- A new study found that older adults with a more fragmented circadian rest-activity rhythm experienced more shrinking of the brain in areas typically affected by Alzheimer’s disease.
Study participants were asked to wear a wrist accelerometer for up to a week to measure their 24-hour rest/activity rhythms, including movement and inactivity, and also had MRI scans taken of three areas of the brain generally affected by Alzheimer’s disease — the parahippocampal gyrus, hippocampus, and
“While disturbed sleep has been linked to poor brain health outcomes, much less is known about how rest-activity rhythms are related to changes in brain structure over time,” Adam Spira, PhD, professor in the Department of Mental Health at the Bloomberg School of Public Health at Johns Hopkins University, and senior author of this study, told Medical News Today.
“We wanted to better understand these associations using MRI measures of brain volume,” said Spira.
Data from the wrist accelerometers allowed scientists to measure how fragmented each participant’s daily rest-activity rhythm was.
“Fragmented rhythms refer to how often a person switches between activity and rest throughout the day,” Marc Kaizi-Lutu, a doctoral researcher in the Department of Mental Health at the Bloomberg School of Public Health at Johns Hopkins University, and co-first author of this study, explained to MNT.
“Someone with more fragmented rhythms tends to more frequently shift between being active and inactive, while someone with less fragmentation has longer, more sustained periods of activity or rest,” Kaizi-Lutu continued.
At the study’s conclusion, researchers found that study participants with less fragmented daily rest-activity rhythms had larger volumes in the memory-associated brain areas the hippocampus and parahippocampus, and less shrinkage of the amygdala, which is vital for emotion.
“These brain regions are particularly vulnerable in Alzheimer’s disease,” Daniel Callow, PhD, assistant professor in the Department of Psychiatry and Behavioral Sciences at the Johns Hopkins University School of Medicine, and co-first author of this study, told MNT.
“Our findings show that individuals with less fragmented and more consistent rest-activity rhythms tend to have larger volumes in these areas and experience less shrinkage of the amygdala over time. Importantly, the longitudinal findings suggest that disrupted rhythms may precede change in brain structure, raising the possibility that more fragmented or less consistent RARs contribute to neurodegeneration.”
– Daniel Callow, PhD
Additionally, scientists observed a correlation between a more fragmented rest-activity rhythm with a quicker increase in the volume of brain ventricles.
“Brain ventricles are fluid-filled spaces that often expand as surrounding brain tissue is lost,” Callow said. “Thus, our finding suggests that more fragmented rest-activity rhythms are associated with faster increases in ventricular size over time, which suggests a link between disrupted daily rhythms and more widespread brain atrophy.”
MNT had the opportunity to speak with Dung Trinh, MD, an internist with MemorialCare Medical Group and chief medical officer of Healthy Brain Clinic in Irvine, CA, about this study.
Trinh, who was not involved in the research, said that this is an important finding because it strengthens the link between circadian rhythm disruption and brain health in aging.
“What stood out most was that more fragmented rest-activity rhythms were associated with smaller volumes in brain regions involved in memory and emotion, and with faster brain atrophy over time, particularly in the oldest adults,” Trinh continued.
“Preserving brain volume is closely tied to preserving memory, independence, emotional well-being, and overall quality of life as people age,“ he explained.
“If researchers can identify modifiable factors that help protect brain structure, it creates opportunities to intervene earlier, before major cognitive symptoms appear. This kind of work helps move the field beyond simply diagnosing decline and toward actively supporting healthier brain aging,” Trinh noted.
“At the same time, I would interpret the study carefully: it shows a strong association, but it does not prove that fragmented circadian rhythms directly cause brain shrinkage,” he added.
For those who may want to potentially help their brain health as they age by having a less fragmented daily rest-activity rhythm, Trinh said his best advice is to aim for regularity by:
- waking up at about the same time every day
- getting bright light exposure in the morning
- staying physically active during the day
- keeping meals and bedtime consistent
- limiting long or late naps
- avoiding caffeine or alcohol too close to bedtime.
“It is also important to talk with a clinician about issues like sleep apnea, insomnia, depression, or medications that can disrupt sleep and daytime alertness,” he added. “The key message is that a stronger, more consistent day-night pattern is generally healthier, even though this study does not prove that improving rhythm regularity will definitely prevent brain atrophy.”
