A new study has found that living in areas with more artificial light at night may increase stress in the brain, inflame blood vessels, and raise the risk of heart disease.
The findings, which will be presented at the American Heart Association’s Scientific Sessions 2025, highlight the growing health risks linked to light pollution in modern cities.
Artificial light at night, often called light pollution, is now nearly unavoidable in urban areas. It comes from streetlights, signs, buildings, and electronic devices, and can disrupt the body’s natural sleep-wake cycle.
While scientists have long known that air and noise pollution affect cardiovascular health, this is one of the first studies to show how nighttime light exposure might harm the heart.
“We know environmental factors such as air and noise pollution can harm heart health through stress and inflammation. Light pollution is very common, but we’ve known little about how it affects the heart,” said Dr. Shady Abohashem, the study’s senior author and a cardiac imaging specialist at Massachusetts General Hospital and Harvard Medical School.
To investigate, researchers studied 466 adults who had no history of heart disease or cancer. Each participant underwent a combined PET/CT scan, which allowed scientists to measure both brain activity and inflammation in blood vessels.
PET scans track metabolic activity in tissues, while CT scans provide detailed images of body structures. This combination let the researchers identify how the brain responds to stress and how the arteries react.
The team compared these results with satellite data showing levels of artificial light near each person’s home, using detailed global maps of nighttime brightness. They found that people living in brighter areas had higher brain stress activity and more inflammation in their arteries. Both of these changes are known to increase the risk of heart attacks and strokes.
The analysis revealed a clear trend: the brighter the nighttime light exposure, the greater the risk. Every standard increase in light exposure was linked with about a 35% higher risk of developing heart disease over five years, and a 22% higher risk over ten years.
These links remained strong even after researchers accounted for other factors such as age, income, and exposure to noise pollution. Over the ten-year follow-up period, 17% of participants experienced major heart problems.
“We found an almost linear relationship between nighttime light and heart disease — the more night light, the higher the risk,” Dr. Abohashem said. “Even modest increases in light exposure were linked with greater brain and artery stress.”
He explained that when the brain senses stress, it sends signals that can trigger immune responses and cause inflammation in blood vessels. Over time, this can contribute to hardening of the arteries, raising the risk of heart attacks and strokes.
The researchers suggested that both city planners and individuals can take steps to reduce exposure to artificial light at night. “Cities can reduce unnecessary outdoor lighting, install shielded lamps, or use motion-sensitive lights,” Abohashem said. “At home, people can keep their bedrooms dark and limit screen use before bed.”
Independent experts praised the study for shedding light on an underexplored environmental risk.
“These findings add to growing evidence that too much nighttime light can disrupt circadian rhythms and harm cardiovascular health,” said Dr. Julio Fernandez-Mendoza of Pennsylvania State University, who was not involved in the research. “This study helps explain how the brain’s stress pathways may link light pollution to heart disease.”
The American Heart Association recently released a scientific statement on circadian health, noting that exposure to artificial light at night can suppress melatonin, delay sleep, and increase the risk of metabolic and cardiovascular problems. Together, these findings point to the importance of darkness for maintaining heart and brain health.
While the study cannot prove that nighttime light directly causes heart disease, it provides important clues about the biological pathways involved. The researchers plan to expand their work in larger, more diverse populations and to test whether reducing nighttime light exposure can improve cardiovascular outcomes.
“This research shows that light pollution is more than an inconvenience—it may be a hidden risk factor for heart disease,” Abohashem said. “Our hope is that by addressing nighttime light exposure, we can make cities and homes healthier for everyone.”
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