Study suggests bright lights at night raises heart attack and stroke risk

By Stephen Beech

Bright lights at night raise the risk of a heart attack or stroke, suggests a new study.

Researchers found that exposure to higher levels of artificial light pollution after dark are linked to increased stress-related activity in the brain, inflamed arteries and a higher risk of heart disease.

Nighttime light pollution is a nearly universal feature of modern cities.

The first-of-its-kind study reviewed brain scans and satellite images to show a "biological pathway" linking nighttime light exposure to heart disease.

Study senior author Dr. Shady Abohashem said: “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.”

The study involved 466 adults with an average age of 55 who had neither heart disease or cancer at the outset.

The amount of nighttime light at each participant's home was measured, as well as stress signals in the brain and signs of artery inflammation on scans.

During the study period, 79 participants (17%) had major heart problems.

All the participants underwent the same combined Positron Emission Tomography/Computed Tomography (PET/CT) scans between 2005 and 2008 and followed up to the end of 2018.

Dr. Abohashem, of Massachusetts General Hospital and an instructor at Harvard Medical School, said, “This is a routine imaging test at my hospital.

“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.”

The analysis found 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 issues.

The greater the artificial night light exposure, the higher the risk of heart disease developing.

The risks were higher among participants who lived in areas with additional social or environmental stress, such as high traffic noise or lower neighborhood income.

Dr. Abohashem said: “We found a nearly linear relationship between night-time light and heart disease: the more night-light exposure, the higher the risk.

"Even modest increases in nighttime light were linked with higher brain and artery stress.

“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.”

To counter the effects of artificial light at night, he suggested that cities could reduce unnecessary outdoor lighting, shield streetlamps or use motion-sensitive lights.

He added: "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 night-time light exposure when developing prevention strategies.

“We want to expand this work in larger, more diverse populations, test interventions that reduce night-time light, and explore how reducing light exposure might improve heart health.

"People can limit indoor night-time light, keeping bedrooms dark and avoiding screens such as TVs and personal electronic devices before bed."

The findings are due to be presented at the annual scientific sessions of the American Heart Association (AHA) in New Orleans.

Dr. Julio Fernandez-Mendoza, who is on the AHA's writing committee, said: "These findings are novel and add to the evidence suggesting that reducing exposure to excessive artificial light at night is a public health concern.

“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.

"This response seems to play a big role in linking artificial light at night to heart disease.”

Dr. Fernandez-Mendoza, of Pennsylvania State University College of Medicine, added: "The findings themselves were not surprising.

"We've known from prior studies, even in animal models, not just in humans, that artificial light exposure at night is associated with worse cardiovascular outcomes, like blood pressure, heart disease, and the like.

"A lot of this evidence in humans comes from night shift workers and people exposed also to neighborhoods with a lot of light exposure, what is called light pollution.

"What this study was novel about 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.

"And one of those is the way that our brain reacts to stress.

"So it does make a lot of sense, their findings, in that people who are too exposed to artificial 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."