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.