Your Body Clock and Brain Health: Why Daily Rhythms Matter for Dementia Risk

A healthy body clock may be more important for brain health in old age than previously thought, with growing evidence linking disrupted daily rhythms to a higher risk of dementia. The body’s internal 24-hour timing system, known as the circadian rhythm, regulates sleep and wake cycles, hormone release, heart rate and body temperature. When this rhythm is well aligned, organs and systems work in sync. When it is disrupted, the consequences may extend beyond poor sleep to long-term effects on the brain.

A large study published in 2025 followed more than 2,000 older adults with an average age of 79. Researchers found that participants with stronger, more regular circadian rhythms had a significantly lower risk of developing dementia over three years. Dementia occurred in about 7% of those with irregular rhythms, compared with around 10% among those with more stable daily patterns. This difference remained even after accounting for heart disease and high blood pressure.

Disrupted circadian rhythms are often linked to sleep problems, which for decades have been suspected to play a role in dementia and cardiovascular disease. Conditions such as sleep apnoea where breathing repeatedly stops during sleep may worsen this risk by reducing oxygen supply to the brain and raising blood pressure. However, separating cause from effect is difficult, as sleep apnoea frequently occurs alongside obesity, diabetes, smoking and alcohol misuse, all of which are known dementia risk factors.

Scientists have proposed several mechanisms to explain the connection between body clocks and brain health. Circadian rhythms influence immune function, which is involved in both heart disease and neurodegeneration. Another theory suggests that sleep helps clear toxic proteins, including amyloid plaques associated with Alzheimer’s disease, from the brain. While this idea is widely discussed, evidence in humans remains mixed.

Importantly, major reviews, including a recent update from The Lancet Commission on dementia prevention, conclude that sleep duration alone is unlikely to be an independent risk factor. Sleeping more or less than average does not consistently predict dementia. Instead, fragmented sleep and disturbed rhythms may sometimes be early warning signs of brain changes that begin years before memory problems appear.

Shift work highlights this complexity. Although it is linked to higher dementia risk, night shift workers do not consistently fare worse than day workers. This suggests that lifestyle factors common in shift work such as poor diet, physical inactivity, stress, smoking and social isolation may be just as important as circadian disruption itself.

Experts caution against relying on sleep medications. Sedatives such as benzodiazepines have been associated with increased dementia risk, falls and accidents, while melatonin has shown inconsistent benefits in older adults.

The most reliable strategy is simple: stay active. About 30 minutes of moderate exercise a day, particularly outdoors and earlier in the day, helps regulate the body clock. Physical activity is also one of the strongest protective factors against heart disease and dementia making it a powerful investment in healthy ageing.