The timing of when a person sleeps—not just how long—plays a vital role in mental health, influencing mood, cognitive function, and overall well-being. A recent study found that misalignment between bedtime and natural sleep preferences can increase the risk of mental health disorders like depression and anxiety.

Researchers identified the chronotype—whether they were morning or evening types—of nearly 74,000 middle-aged and older adults enrolled in the UK Biobank. They tracked sleep patterns using accelerometry and evaluated their sleep and chronotype alignment. They assessed mental health outcomes through standard diagnostic codes.

They found that morning types who went to bed late had a greater risk of mental health disorders, including depression and anxiety, than those whose sleep timing matched their chronotype. Interestingly, evening types who went to bed early had a lower risk of depression and a trend toward reduced risks of other mental health issues.

These findings suggest a mismatch between one’s biological preferences and sleep schedule can harm mental well-being. The investigators posited that people should aim to sleep before 1 a.m. for optimal mental health, even if their natural chronotype favors later sleep. Learn more about chronotypes in this clip featuring Dr. Matthew Walker.