Inside the body, a 24-hour rhythm, known as the circadian rhythm, quietly coordinates when we sleep, wake, eat and recover. This internal timing system helps keep organs and hormones working in sync. When it becomes disrupted, the effects may extend well beyond poor sleep, with growing evidence suggesting consequences for long-term brain health.
A large 2025 study of more than 2,000 people with an average age of 79 found that those with a strong circadian rhythm had an almost halved risk of developing dementia. Circadian rhythms regulate daily processes including sleep timing, hormone release, heart rate and body temperature.
Over three years of follow-up, people with weaker or more disrupted circadian rhythms were more likely to develop dementia than those with stronger, more stable daily rhythms.
Disrupted circadian rhythms are often associated with poor sleep. For decades, poor sleep has been suspected to contribute to both dementia and heart disease, which share several underlying risk factors. In the 2025 study, worse heart health and high blood pressure, both commonly linked to sleep disruption, were accounted for in the analysis. Sleep apnoea, however, was not.
Sleep apnoea is a common condition in which breathing repeatedly stops and starts during sleep, reducing oxygen supply to the brain and raising blood pressure. Its relationship with dementia remains debated, largely because sleep apnoea is more common in people who already have established dementia risk factors such as obesity, diabetes, smoking and alcohol misuse. This overlap makes it difficult to determine whether sleep apnoea itself increases dementia risk or whether it reflects broader metabolic and cardiovascular vulnerability.
This review suggested that addressing physical inactivity linked to fatigue from disrupted sleep may be a promising approach. Increasing activity could reduce obesity, improve sleep quality and support brain cell health, potentially lowering dementia risk through several pathways at once.
Article continues on The Conversation: www.theconversation.com/your-body-clock-matters-for-brain-health-in-later-life-and-could-even-be-linked-to-dementia-risk-272838
