According to research published in JAMA Network Open, scientists working with data from the UK Biobank tracked nearly 89,000 adults over the age of 40 for close to ten years.
None of the participants had cardiovascular disease when the project began.
Each year, volunteers wore a small device for one week that measured how much light they encountered during the overnight hours.
When investigators reviewed health records over time, they saw a consistent pattern.
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People who slept in brighter environments were more likely to develop several forms of cardiovascular disease.
Those conditions included coronary artery disease, heart failure, atrial fibrillation, and stroke.
The study did not prove that nighttime light directly causes these problems, but the association remained strong even after adjusting for age, physical activity, diet, income, and other lifestyle factors.
Researchers noted that women and younger participants showed some of the steepest increases in risk.
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The authors wrote that reducing exposure to light at night may be a useful addition to existing heart-health recommendations.
Why light matters for the body
Scientists suspect that even modest brightness at night can disrupt the body’s circadian rhythm.
The circadian rhythm the internal system that helps regulate sleep, metabolism, hormone release, and cardiovascular function.
Earlier studies have linked nighttime illumination with higher chances of developing type 2 diabetes, adding weight to the idea that light can influence more than sleep quality alone.
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Simple ways to sleep in the dark
While the findings stop short of proving cause and effect, experts say it makes sense to examine how much light filters into the bedroom.
Beyond switching off screens earlier in the evening, small adjustments may help.
Using blackout curtains, wearing a sleep mask, or dimming lamps well before bedtime.
The study also found a counterbalancing trend, participants who spent more time in bright daylight had lower cardiovascular risks.
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That adds one more reason to step outside early and often.
Sources: Real Simple, JAMA Network Open.
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