The Health Effects of Daylight Saving Time on Your Sleep

The human body runs on a roughly 24-hour internal clock called the circadian rhythm, and it is exquisitely sensitive to light. When we shift the clocks by an hour, we're effectively asking millions of people to jet-lag themselves overnight — and the research shows the body notices.

Sleep disruption

Studies consistently show that people sleep less in the days after the spring forward — often 15 to 40 minutes less — and that sleep quality drops. The effect lingers for several days as the circadian system slowly realigns to the new clock time. The fall back is easier on total sleep but can still throw off timing.

Short-term health risks

A body of research has linked the spring transition to a temporary rise in cardiovascular events, including heart attacks, in the days immediately after. Other studies have noted brief increases in traffic accidents and workplace injuries around the time change, likely tied to lost sleep and darker commutes.

Even a single hour of sleep loss can measurably affect reaction time, mood, and alertness — and the spring forward is the worst offender.

Mood and mental health

Light exposure is closely tied to mood. The shift in daylight timing can worsen symptoms for people prone to seasonal affective patterns, especially in the darker evenings after the fall back. Consistent morning light and steady sleep schedules are the best defenses.

How to protect your sleep

• Adjust bedtime gradually by 15 minutes a day for several days before the change.
• Prioritize bright morning light to anchor your rhythm.
• Keep a consistent wake time, even on weekends.
• Limit screens and bright light in the hour before bed during transition weeks.

The health debate is a major reason researchers and lawmakers keep revisiting whether twice-yearly time changes are worth it at all.