Nighttime light exposure linked to higher risk of death, study finds

Exposure to bright light at night, including light from screens and illuminated bedrooms, may be associated with a higher risk of mortality, according to a study that examined the relationship between nighttime light exposure and the body’s internal clock.

The research, published in Proceedings of the National Academy of Sciences, analyzed light exposure patterns among 88,905 adults from the UK Biobank and followed them for approximately eight years.

Researchers found that people exposed to the highest levels of light at night had a 21% to 34% higher risk of death from any cause compared with those who spent their nights in darker environments.

The researchers linked the findings to circadian rhythms, the internal system that helps regulate when the body stays awake and when it rests. According to Andrew Phillips, an associate professor at Flinders University and a lead author of the study, disruption of these rhythms has been associated with metabolic syndrome, diabetes and obesity, as well as cardiovascular conditions including heart attacks, strokes and hypertension.

The study also found that greater exposure to natural light during the day was generally associated with a lower risk of mortality. A combination of brighter nights and darker days was associated with greater disruption of circadian rhythms.

Researchers recorded participants’ light exposure using wrist-worn sensors for one week and later compared those patterns with available mortality records.

The findings do not mean that people need to sleep in complete darkness, but researchers recommend reducing exposure to bright artificial light before bed and during sleep. Keeping the bedroom dark, limiting screen exposure and getting sufficient natural light during the day may help support a healthier sleep routine.