Turning off the lights at night has long been linked to better sleep, but new research suggests it may also protect the heart. Sleeping in complete darkness could lower the risk of cardiovascular disease, the leading cause of death worldwide.
The study found that adults who slept in the brightest conditions—comparable to having overhead lights on—had a 56% higher risk of heart failure. They also faced a 32% greater risk of coronary artery disease and a 28% higher risk of stroke. Participants exposed to bright light at night had a 47% higher risk of heart attack and a 32% higher risk of atrial fibrillation (A-fib), an irregular heartbeat. Women were more prone to heart failure and coronary artery disease, while younger adults were more affected by heart failure and A-fib.
Researchers tracked nearly 89,000 people using wrist-worn light sensors between 12:30 a.m. and 6 a.m. for a week, then followed them for about nine years. The study controlled for physical activity, smoking, alcohol, diet, shift work, and other factors.
“Light at night can suppress melatonin, disrupt circadian rhythms, and affect cardiovascular health,” said Dr. Daniel Windred, co-first author from Flinders University in Australia. Circadian disruption can raise blood pressure, stress hormones, and the risk of clot formation, all of which can contribute to strokes, heart attacks, and other heart conditions.
Experts recommend minimizing nighttime light exposure by turning off unnecessary lights, using dim or warm lighting, avoiding bright alarm clocks, and installing blackout curtains or wearing a sleep mask. Limiting screen time before bed can also help.
The study also noted that high light exposure during the day may support heart health, highlighting the importance of natural daylight. While the findings show a strong link between night light and cardiovascular risk, researchers caution that further studies are needed, especially in more diverse populations, to fully understand the effects of light on heart health.
