Researchers have discovered that people exposed to brighter light at night face up to 50% higher risks of heart disease, while daytime light may protect the heart by reinforcing healthy circadian rhythms.
The new study, published in Nature Aging, examined over 283,000 adults aged 40 and above from the UK Biobank database. Using satellite data to measure outdoor nighttime brightness and wearable devices to monitor individual light exposure, the researchers found a strong association between exposure to bright nights and increased rates of heart failure and stroke.
According to the study, individuals living in areas with high levels of artificial night light had significantly higher rates of cardiovascular disease, even after adjusting for factors such as income, pollution, sleep duration, and lifestyle habits.
The researchers propose that excessive nighttime light disrupts circadian rhythms—the body’s natural day-night cycle—which can interfere with blood pressure regulation, glucose metabolism, and inflammatory responses, thereby increasing cardiovascular risks.
Interestingly, the findings also revealed that people exposed to brighter daytime light, particularly natural sunlight, exhibited better cardiovascular health outcomes. Strong daytime light appears to strengthen circadian rhythms and offset some of the adverse effects of nighttime light exposure.
Lead author Dr. Tianyi Huang of Harvard Medical School emphasized that the results highlight the importance of aligning light exposure with natural day-night cycles. “Modern society often exposes us to artificial light at night and insufficient daylight during the day. Both can impact our internal biological clock and, over time, our cardiovascular health,” he explained.
