You probably know that a good night’s sleep is crucial for your health, but have you considered how much light you’re exposed to after the sun goes down? The largest study of its kind has found a direct link between nighttime light exposure and an increased risk of heart disease, suggesting that our 24/7 society may be disrupting our health in serious ways.
💡 Measuring Personal Light Exposure
Previous studies linked bright urban areas to heart disease but only measured outdoor light. This new study, however, tracked nearly 89,000 people who wore personal light sensors for a week. These sensors captured all light in their environment, including artificial light from overhead lamps and even phones. This provided a much more accurate picture of an individual’s actual light exposure patterns.
📈 A Stark Connection to Heart Health
The results were striking. Over an eight-year follow-up period, individuals with the highest exposure to light at night had a **23 to 56 per cent higher risk** of developing cardiovascular disease than those with the darkest nights. This association was independent of other factors like sleep duration, age, or smoking, pointing to night light exposure as a key driver of the risk. Even short exposures, like turning on a light for an hour between midnight and 6 am, could place someone in the highest risk group.
🕰️ Disrupting Your Internal Clock
Why does this happen? Light is a major enforcer of our **circadian rhythms**, the internal clocks that govern our bodies. Exposure to light at the wrong time can disrupt these clocks, which can impair glucose tolerance, affect blood pressure, and increase the risk of abnormal heart rhythms. The good news is that the solution is simple: try to make your nights darker by using dim, warm lighting if you need to get up.
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Thomson, Helen. “Nighttime light exposure linked to heart disease.” New Scientist, vol. 267, no. 3551, 12 July 2025, p. 9.
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