A large-scale study by Flinders University analyzed over 13 million hours of light exposure data from 88,905 people aged 40 and older, revealing that bright light at night significantly increases the risk of heart failure and heart attack. Those exposed to the highest levels of nighttime light (measured in lux) had a 56% greater chance of heart failure and a 47% higher risk of heart attack compared to those with the least exposure. The study, the largest of its kind, found that disrupting the body’s circadian rhythm by exposure to light during typical dark hours is a strong, independent risk factor for heart disease.
The researchers categorized light exposure using lux, with a dark night sky under 0.01 lux and a well-lit room exceeding 100 lux. Participants with median nighttime exposure above 105.3 lux (91st-100th percentile) had the worst cardiovascular outcomes. The effect was particularly pronounced in younger adults and women, who may be more sensitive to circadian disruption.
Conversely, bright daylight exposure was linked to protective cardiovascular benefits, lowering risks of coronary artery disease, heart failure, and stroke by 13-28% before adjusting for lifestyle factors. The findings reinforce the importance of maintaining natural sleep rhythms and suggest that reducing nighttime light exposure could be a powerful strategy for preventing heart disease. The researchers recommend further investigation and guidelines for light usage in homes, hospitals, and cities to protect cardiovascular health.
The published study is available here.
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