Exposure to artificial light at night appears to trigger stress in the brain and inflammation in the arteries, raising heart disease risk. Researchers say even modest light increases could have long-term cardiovascular consequences.
Higher exposure to artificial light at night was associated with increased stress activity in the brain, inflammation in the arteries, and a greater risk of heart disease, according to a preliminary study presented recently at the American Heart Association’s Scientific Sessions 2025.
Why Artificial Light at Night Matters
Artificial light at night, often referred to as nighttime light pollution, is nearly unavoidable in modern urban environments, the researchers noted. In this first-of-its-kind investigation, scientists combined brain imaging with satellite data to identify a biological pathway that may connect nighttime light exposure to heart disease.
“We know that environmental factors, such as air and noise pollution, can lead to heart disease by affecting our nerves and blood vessels through stress. Light pollution is very common; however, we don’t know much about how it affects the heart,” 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.
How Researchers Measured Brain Stress and Artery Inflammation
All participants underwent the same Positron Emission Tomography/Computed Tomography (PET/CT) scan. The study included 450 adults who had no history of heart disease and no active cancer. “This is a routine imaging test at my hospital,” Abohashem said. “The CT portion provides detailed anatomy, while the PET portion reveals metabolic activity in tissues. Using both imaging techniques together allows for the measurement of brain stress activity and arterial inflammation in a single scan.”
Key Findings From the Analysis
The results showed that people exposed to higher levels of artificial light at night had increased stress-related activity in the brain, more inflammation in blood vessels, and a higher likelihood of major cardiovascular events. Researchers gathered this information from medical records, which were independently reviewed by two blinded cardiologists who did not know any details that could influence their evaluations.
Risk rose steadily with increasing light exposure. Each standard deviation increase in nighttime light was linked to roughly a 35% higher risk of heart disease over five years and a 22% higher risk over ten years. These relationships remained even after accounting for traditional heart disease risk factors and other social and environmental influences such as noise pollution and socioeconomic status.
The association was strongest among participants living in areas with additional stressors, including heavy traffic noise or lower neighborhood income. Over a ten-year follow-up period, 17% of participants experienced major heart-related conditions.
A Stress Driven Pathway Linking Light and the Heart
“We found a nearly linear relationship between nighttime light and heart disease: the more night-light exposure, the higher the risk. Even modest increases in night-time light were linked with higher brain and artery stress,” Abohashem said. “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.”
Reducing Exposure at Home and in Communities
To lessen the impact of artificial light at night, Abohashem suggested that cities reduce unnecessary outdoor lighting, shield streetlamps, or install motion sensitive lighting systems. On an individual level, “people can limit indoor nighttime light, keeping bedrooms dark and avoiding screens such as TVs and personal electronic devices before bed,” he said.
Expert Perspective on Public Health Implications
“These findings are novel and add to the evidence suggesting that reducing exposure to excessive artificial light at night is a public health concern,” said Julio Fernandez-Mendoza, Ph.D., DBSM, FAHA, who serves on the writing committee of Multidimensional Sleep Health: Definitions and Implications for Cardiometabolic Health: A Scientific Statement From the American Heart Association.
Circadian Health and Cardiovascular Risk
Previously, the American Heart Association released a scientific statement on the Role of Circadian Health in Cardiometabolic Health and Disease Risk. The statement highlights light pollution as a major disruptor of the body’s internal clock and notes that it can suppress melatonin, delay the onset of sleep, and even at low levels has been linked to an increased risk of cardiovascular disease.
“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,” Fernandez-Mendoza said. “This study has investigated one of several possible causes, which is how our brains respond to stress. This response seems to play a big role in linking artificial light at night to heart disease.” Fernandez-Mendoza, who was not involved in the research, is also a professor of psychiatry, neuroscience, and public health sciences and director of behavioral sleep medicine at Pennsylvania State University College of Medicine in Hershey, Pennsylvania.
Strengths and Limitations of the Study
The research benefited from advanced PET/CT imaging to assess brain stress and arterial inflammation, combined with satellite-based measurements of nighttime light and long-term follow-up for cardiovascular events.
There were also limitations. The study was observational and relied on previously collected data, meaning it cannot establish a direct cause-and-effect relationship. In addition, all participants received care within a single hospital system, which limits the extent to which the findings can be generalized to more diverse populations.
Study Population and Data Sources
Researchers reviewed health records from 466 adults, 43% of whom were men, with a median age of 55. Among participants, 89.7% were white, and 10.3% were non-white. All underwent a PET/CT scan at Massachusetts General Hospital in Boston between 2005 and 2008.
Nighttime light exposure was estimated using data from the 2016 New World Atlas of Artificial Night Sky Brightness. This resource combines upward radiance measurements from the Visible Infrared Imaging Radiometer Suite Day/Night Band on the Suomi National Polar-orbiting Partnership satellite with radiative transfer modeling to estimate ground-level zenith sky brightness. Artificial brightness refers only to light produced by human sources and excludes natural light from stars, airglow, and moonlight.
Researchers measured nighttime light levels at each participant’s home and analyzed imaging markers of brain stress and arterial inflammation. Participants were followed through the end of 2018, during which time 79 individuals, or 17%, experienced major heart problems.
Looking Ahead
“This research indicates that light pollution is more than just an annoyance; it could also increase the risk of heart disease. We hope clinicians and policymakers will consider nighttime light exposure when developing prevention strategies,” Abohashem said. “We want to expand this work in larger, more diverse populations, test interventions that reduce nighttime light, and explore how reducing light exposure might improve heart health.”
Meeting: American Heart Association Scientific Sessions 2025
The study featured in this article is a research abstract. Abstracts presented at American Heart Association’s scientific meetings are not peer-reviewed, and the findings are considered preliminary until published as full manuscripts in a peer-reviewed scientific journal.
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1 Comment
“Nighttime light exposure was estimated using data from the 2016 New World Atlas of Artificial Night Sky Brightness…Researchers measured nighttime light levels at each participant’s home..” Did they enter the bedroom and measure the light there, or just outside the home? Did the participants use shades to block the light? These are critical questions that are not clear in this article, and there is no written abstract offered to read.
“The association was strongest among participants living in areas with additional stressors, including heavy traffic noise..” However, they did not seem to check for air pollution, which goes along with traffic noise. Air pollution is known to irritate blood vessels and can lead to heart disease. This was not controlled for in this study.
I hate nighttime light, but this study doesn’t hold up to scrutiny.