Nighttime Artificial Light Exposure Linked to Increased Heart Disease Risk Through Brain Stress Response

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. The research, conducted at Massachusetts General Hospital, represents the first investigation to demonstrate a biological pathway connecting nighttime light exposure to cardiovascular problems.

The study analyzed 450 adults without pre-existing heart disease who underwent combined Positron Emission Tomography/Computed Tomography (PET/CT) scans between 2005 and 2008. Researchers 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. 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.

"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 in Boston. "When the brain perceives stress, it activates signals that can trigger an immune response and inflame the blood vessels. Over time, this process can contribute to hardening of the arteries and increase the risk of heart attack and stroke."

The research team 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 amount of nighttime light at each person's home was measured alongside stress signals in the brain and signs of artery inflammation on scans.

During the follow-up period ending in 2018, 17% of participants developed major heart conditions. 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. These associations remained significant even after accounting for traditional risk factors and other socio-environmental exposures.

Julio Fernandez-Mendoza, Ph.D., DBSM, FAHA, who serves on the writing committee of the Multidimensional Sleep Health: Definitions and Implications for Cardiometabolic Health scientific statement, 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," said Fernandez-Mendoza, who was not involved in the study. "This study has investigated one of several possible causes, which is how our brains respond to stress."

The findings align with recent American Heart Association scientific statements, including last week's statement on the Role of Circadian Health in Cardiometabolic Health and Disease Risk, which identified light pollution as a major factor disrupting body clocks and increasing cardiovascular disease risk. Researchers suggest that cities could reduce unnecessary outdoor lighting, shield streetlamps or use motion-sensitive lights to counter the effects of artificial light at night. On a personal level, people can limit indoor nighttime light, keeping bedrooms dark and avoiding screens before bed.

While the study provides important insights, researchers note limitations including its observational nature, which prevents establishing direct cause-and-effect relationships, and the limited diversity of the participant group, with 89.7% of participants being white. The research team plans to expand this work in larger, more diverse populations and test interventions that reduce nighttime light exposure to determine how such reductions might improve heart health outcomes.