Another reason to darken those windows and shut down those screens at bedtime: Increased exposure to artificial light at night may increase the risk for cardiovascular disease (CVD), researchers have found.

The retrospective, observational study showed exposure to artificial light — from screens, streetlamps, and other sources — at night appears to boost inflammation in the arteries and trigger stress responses in the brain, thereby putting strain on the cardiovascular system. People with the most exposure to light at night had a 35% increased risk for a major cardiovascular event after 5 years, and a 22% increased risk after 10 years, according to the analysis. 

“Our study is the first to link outdoor light pollution to an active biological pathway that may contribute to cardiovascular disease,” said Shady Abohashem, MD, MPH, head of cardiac PET/CT imaging trials at Massachusetts General Hospital of Harvard Medical School in Boston. “Prior research has shown that light at night disrupts our body’s natural circadian rhythm, while our work demonstrates that it also activates stress centers in the brain and triggers inflammation in the arteries, a combination that we’ve previously found to increase heart disease risk.” 

Although the analysis was observational and cannot prove causality, the results support the idea that reducing exposure to artificial light at night may quiet stress pathways in the brain and arterial inflammation, which may translate into a lower risk for developing CVD, Abohashem said. 

“For individuals living in areas with high light pollution, we recommend minimizing unnecessary sources of artificial light. That means keeping the bedroom as dark as possible, using blackout blinds, eye masks, dimming lighting, and reducing screen time in the hours before sleep,” he said. 

Abohashem will present the study November 10 at the American Heart Association’s 2025 Scientific Sessions in New Orleans. 

Artificial light at night is a universal feature of modern cities and has been shown to be linked to cardiometabolic disorders, yet its independent contribution to CVD remains uncertain. 

For the new study, Abohashem and colleagues aimed to investigate the link between artificial light at night and elevated stress-related neural activity, arterial inflammation, and future risk for major adverse cardiovascular events.

The study involved 466 adults (median age 55 years, 43% men) who underwent a combined PET/CT scan at Massachusetts General Hospital between 2005 and 2008. Individuals who had cancer or CVD at baseline were excluded from the analysis. 

These imaging techniques allow for the measurement of stress-related neural activity and arterial inflammation in a single scan, Abohashem said. 

Stress-related neural activity was quantified as the amygdala-to-cortical activity ratio, and arterial inflammation was assessed as the aortic target-to-background ratio.

Artificial light at night was calculated for each participant using their home address and with data from the New World Atlas of Artificial Night Sky Brightness.

Results were adjusted for traditional cardiovascular risk factors, socio-environmental characteristics — air and noise pollution, income, and how urban their neighborhood is — and medical covariates.

During the 10-year follow-up period, 79 participants (17 %) experienced a major adverse cardiac event. 

Results showed that each one standard deviation higher level of exposure to artificial light at night was independently associated with higher stress-related neural activity (standardized β 0.14; 95 % CI, 0.01-0.27; P = .03) and greater arterial inflammation (standardized β 0.09; 95% CI, 0.00-0.17; P = .04).

In addition, higher levels of artificial light at night were associated with increased rates of major adverse cardiovascular events at both the 5-year (hazard ratio [HR], 1.35; 95% CI, 1.05-1.74) and 10-year mark (HR, 1.22; 95% CI, 1.01-1.50).

“We found that higher exposure to artificial light pollution was associated with a 35% increased risk of cardiovascular disease over 5 years follow-up, and 22% increased risk over 10 years follow-up,” Abohashem said. 

People who are exposed to high levels of light pollution often also experience other forms of stress, like noise or socio-economic deprivation. “We found that these other stressors did not account for the effect of the light pollution but had an independent additive effect,” Abohashem said. 

In addition to individuals making changes to avoid artificial light at night, Abohashem said municipalities could implement strategies to help ameliorate the risk, such as reducing unnecessary outdoor lighting, shielding streetlamps, or using motion-sensitive lights.

“Getting regular exposure to natural morning light is equally important, as it helps reset the body’s internal clock. These simple steps can help restore healthy circadian rhythms, which should support better heart health,” he added. 

‘Novel Findings’

Julio Fernandez-Mendoza, PhD, director of behavioral sleep medicine at Pennsylvania State University College of Medicine in Hershey, called the new findings “novel” but “not surprising.” 

Previous studies have shown that artificial light exposure at night is associated with worse cardiovascular outcomes, with much of this evidence coming from night shift workers and people living in areas with significant light pollution. 

“What is novel about this study is that, for the first time, they examined one of the potential mechanisms by which that exposure to artificial light at night is related to inflammation and heart disease,” Fernandez-Mendoza said. 

“And one of those is the way that our brain reacts to stress,” he said. For people overexposed to light at night, “their brain responds to it as if it was a stressor, and therefore it creates this cascade, this chain reaction in which our cardiovascular system suffers,” he said. 

Abohashem is supported in part by the American Heart Association’s Second Century Early Faculty Independence Award. Fernandez-Mendoza reported no relevant financial relationships.