Higher levels of exposure to artificial light at night were linked to increased stress-related activity in the brain, inflamed arteries and a higher risk of heart disease, according to a preliminary study to be presented at the American Heart Association's Scientific Sessions 2025. This research provides new insights into how light pollution, a nearly universal feature of modern cities, affects cardiovascular health through biological pathways.
The study of 450 adults in Boston found that people exposed to higher levels of artificial light at night had higher brain stress activity, blood vessel inflammation and a higher risk of major heart events. Researchers used combined Positron Emission Tomography/Computed Tomography (PET/CT) scans to measure brain stress activity and arterial inflammation in participants without pre-existing heart disease or active cancer.
"We found a nearly linear relationship between nighttime light and heart disease: the more night-light exposure, the higher the risk," said study senior author Shady Abohashem, M.D., M.P.H., head of cardiac PET/CT imaging trials at Massachusetts General Hospital and an instructor at Harvard Medical School. "Even modest increases in night-time light were linked with higher brain and artery stress."
The analysis revealed that every standard deviation increase in light exposure was associated with about 35% and 22% increased risk of heart disease over five- and 10-year follow-up periods, respectively. These associations remained significant even after accounting for traditional risk factors and other socio-environmental exposures like noise pollution and socioeconomic status. Over a 10-year follow-up period, 17% of participants developed major heart conditions.
The biological mechanism appears to involve the brain's stress response system. "When the brain perceives stress, it activates signals that can trigger an immune response and inflame the blood vessels," Abohashem explained. "Over time, this process can contribute to hardening of the arteries and increase the risk of heart attack and stroke."
The study used exposure data obtained from the 2016 New World Atlas of Artificial Night Sky Brightness, which integrates upward radiance data from satellite imaging to estimate ground-level zenith sky brightness. The research team measured the amount of nighttime light at each participant's home address and correlated this with stress signals in the brain and signs of artery inflammation visible on the scans.
Julio Fernandez-Mendoza, Ph.D., who serves on the writing committee of the American Heart Association's scientific statement on Multidimensional Sleep Health, noted the significance of these findings. "We know too much exposure to artificial light at night can harm your health, particularly increasing the risk of heart disease. However, we did not know how this harm happened. This study has investigated one of several possible causes, which is how our brains respond to stress."
The heart risks were particularly elevated among participants who lived in areas with additional social or environmental stress, such as high traffic noise or lower neighborhood income, suggesting that light pollution may compound other environmental stressors.
While the study has limitations as an observational analysis that cannot prove direct cause-and-effect relationships, and the participant group may not represent diverse populations, the findings point to practical solutions. Researchers suggest that cities could reduce unnecessary outdoor lighting, shield streetlamps or use motion-sensitive lights. On a personal level, people can limit indoor nighttime light, keep bedrooms dark and avoid screens before bed.
This research comes shortly after the American Heart Association issued a scientific statement on the Role of Circadian Health in Cardiometabolic Health and Disease Risk, which also identified light pollution as a major factor disrupting body clocks and increasing cardiovascular disease risk.
"This research indicates that light pollution is more than just an annoyance; it could also increase the risk of heart disease," Abohashem said. "We hope clinicians and policymakers will consider nighttime light exposure when developing prevention strategies." The study team plans to expand this work in larger, more diverse populations and test interventions that reduce nighttime light exposure to determine how such measures might improve heart health outcomes.
