Sleeping with lights on? Study says it could harm your heart

For most of human history, night meant darkness - a cue for the body to rest, repair, and reset. But modern life has rewritten that rule. Bedroom lamps glow softly, phone screens stay on till midnight, and even through the curtains, city lights shimmer like a second sunset. It feels harmless. Yet science is now revealing that this quiet glow could be doing real damage - not to your eyes, but to your heart.

A preliminary study presented at the American Heart Association’s 2025 Scientific Sessions has found that exposure to artificial light at night, even at modest levels, is linked to higher stress activity in the brain and greater inflammation in blood vessels. Over time, this can harden arteries, a proven pathway toward heart attacks and strokes.
Video
What explains this link?
Researchers from Harvard Medical School and Massachusetts General Hospital tracked 466 adults, comparing brain and artery scans with satellite data showing how bright their neighbourhoods were at night. The results were striking: people exposed to more night-time light had a 35% higher risk of developing heart disease within five years.

Lead researcher Dr. Shady Abohashem explained that increase in night-time light exposure translated to about a 35% higher risk of heart disease within five years and a 22% increased risk over ten years. In total, 17% of the study group experienced major heart conditions during follow-up. Those living in areas burdened with additional social or environmental stresses such as heavy traffic noise or low neighborhood income faced even greater risks.

The glow of 24/7 living has become part of the urban landscape. Late-night gym classes, glowing digital billboards, and always-on devices mean most city dwellers never experience true darkness. Light pollution - what was once a purely environmental issue is now creeping into our bedrooms and biology.

Reclaiming the dark
Lifestyle experts now call it the “light diet”: learning to manage how much illumination your body consumes after sunset. Just like cutting back on caffeine or sugar, reducing artificial light at night can help your body return to its natural rhythm. Small changes can make a difference.

• Keep your bedroom as dark as possible. Use blackout curtains, eye mask, and avoid night lights unless absolutely necessary.
• Switch off phones, TVs, tablets, and other glowing electronics at least 30-60 minutes before bed.
• Limit outdoor light pollution around your home, swap bright LEDs for warmer tones in the evening.
• Be mindful of other environmental stressors, such as noise, which can amplify risks.

While these studies are observational and can't conclusively prove cause and effect, the strong and consistent associations suggest that reducing artificial light exposure at night is an actionable public health opportunity worth serious consideration. Some urban planners are even exploring “dark design” street lighting that keeps roads safe while protecting residents’ circadian health. In parts of Europe, “dark sky” towns are becoming wellness destinations, where travellers can sleep under stars instead of streetlights.

Science has long told us to eat better and move more for heart health. But the new frontier may be simpler: turn off the lights. Darkness isn’t just for sleep - it’s for healing. In a world where brightness has become a sign of progress, rediscovering the dark might just be the most modern thing you can do for your heart.