January 14, 2026
Our circadian rhythms, the internal body clock that determines when we are most active and alert and when we wind down and go to sleep during a typical 24-hour day, may play a role in our risk of dementia, according to a new report. The study found that people with less regular circadian rhythms, as well as those whose activity levels peaked later in the afternoon, were at increased risk of developing Alzheimer’s disease and other forms of dementia.
“Changes in circadian rhythms happen with aging, and evidence suggests that circadian rhythm disturbances may be a risk factor for neurodegenerative diseases like dementia,” said study author Wendy Wang of UT Southwestern Medical Center in Dallas. “Our study measured these rest-activity rhythms and found people with weaker and more fragmented rhythms, and people with activity levels that peaked later in the day, had an elevated risk of dementia.”
Circadian rhythms are guided by the brain and regulate the roughly 24-hour sleep-wake cycle as well as body processes like hormone levels, digestion and body temperature. Exposure to light and the changing seasons, as well as work schedules and other demands, can affect this internal body clock.
In someone with a strong circadian rhythm, the body clock aligns well with the 24-hour day, and sleep and wake times tend to be steady. In those with a weak circadian rhythm, schedule or seasonal changes are more likely to disrupt the body clock, resulting in greater shifts in sleep times and activity levels.
For the study, researchers tracked 2,183 seniors who were part of an ongoing community heart study. Their average age was 79. None had Alzheimer’s disease or other forms of dementia at the study’s start. Participants wore heart monitors that tracked their sleep and activity levels over a 12-day period, and the researchers assessed the strength of their circadian rhythms.
Over the next three years, 176 of the participants developed Alzheimer’s disease or other form of dementia. After adjusting for factors such as age, blood pressure and heart disease, the researchers found that those with weaker circadian rhythms had nearly two-and-a-half times the risk of developing dementia compared to those with strong circadian rhythms.
In addition, those whose peak activity levels occurred later in the afternoon, from 2:15 p.m. or later, had a 45 percent higher risk of developing dementia than those who peaked earlier in the afternoon, between 1:11 p.m. and 2:14 p.m. Ten percent of those in the late afternoon group developed dementia, compared with 7 percent in the early afternoon group. The researchers say that late-afternoon peak activity levels may reflect greater disruptions in the internal body clock.
“Disruptions in circadian rhythms may alter body processes like inflammation, and may interfere with sleep, possibly increasing amyloid plaques linked to dementia, or reducing amyloid clearance from the brain,” Dr. Wang said.
The study showed only an association between weak circadian rhythms and increased dementia risk and cannot prove cause and effect. But the findings, published in the journal Neurology, build on earlier research showing that sleep disruptions may raise the risk of developing dementia. People with sleep apnea, for example, which causes people to stop breathing and wake up for brief periods during the night, are at increased risk of developing Alzheimer’s disease. Daytime sleepiness or long afternoon naps have likewise been linked to an increased risk of dementia.
“Future studies should examine the potential role of circadian rhythm interventions, such as light therapy or lifestyle changes, to determine if they may help lower a person’s risk of dementia,” Dr. Wang said.
By ALZinfo.org, The Alzheimer’s Information Site. Reviewed by Eric Schmidt, Ph.D., Fisher Center for Alzheimer’s Research Foundation at The Rockefeller University.
