It’s easy to think of city lights as harmless or even comforting, but new research suggests the glow from streetlights, billboards, and even our own devices after dark could be quietly affecting our hearts.
A study led by researchers at Massachusetts General Hospital and funded by the American Heart Association (AHA) has linked higher exposure to nighttime artificial light with increased risk of heart disease.
How the Study Tracked Light and Heart Health
To explore this connection, researchers looked at data from 466 adults with a median age of 55 who had undergone PET/CT scans between 2005 and 2008.
These scans allow doctors to measure both brain stress activity and inflammation in the arteries—two important markers for heart health.
The team compared these results with satellite images and other data measuring how much artificial light each person was exposed to at home at night.
Importantly, this measurement excluded natural light sources like the moon or stars.
By 2018, follow-up data showed that 79 participants, or 17%, had developed major heart problems.
The analysis revealed a clear pattern: the more nighttime light participants were exposed to, the higher their brain stress levels, artery inflammation, and risk of heart disease.
Light Exposure Raises Heart Disease Risk
The study found that even modest increases in nighttime light exposure were linked to elevated risks.
Over five years, risk increased by about 35%, and over ten years, by 22%.
Dr. Shady Abohashem, head of cardiac PET/CT imaging trials at Massachusetts General Hospital, explained:
“We saw a nearly linear relationship between night-light exposure and heart disease.
The more exposure, the greater the risk. Even small increases were associated with higher stress in the brain and arteries.”
Stress signals from the brain can trigger inflammation in blood vessels, which over time may lead to hardening of the arteries, increasing the likelihood of heart attacks and strokes.
Environmental Stress Adds Fuel to the Fire
The research also noted that participants living in areas with additional stressors, such as high traffic noise, faced even greater risks. Dr. Abohashem suggested that cities could reduce unnecessary outdoor lighting or consider streetlights with motion sensors to help curb these risks.
“Light pollution is more than just an annoyance,” he said. “It could genuinely raise the risk of heart disease.
Clinicians and policymakers should consider nighttime light exposure when planning prevention strategies.”
Coronary Artery Disease Explained
Coronary artery disease (CAD) occurs when major blood vessels that supply the heart with oxygen and nutrients become blocked or inflamed, often due to plaque buildup.
CAD affects millions globally—over 1.6 million men and 1 million women in the UK alone, and 15 million adults in the US.
Symptoms may be subtle at first, but as arteries narrow, people can experience chest pain, shortness of breath, or angina.
Complete blockages can trigger heart attacks. Common risk factors include smoking, diabetes, high blood pressure, inactivity, and poor diet.
Prevention focuses on lifestyle changes such as quitting smoking, managing health conditions, staying active, and eating a balanced diet.
Medications can help lower cholesterol or thin the blood, while procedures like stents or coronary bypass surgery may be necessary in severe cases.
Simple Steps to Reduce Light Exposure at Home
Dr. Abohashem also recommended practical steps to limit indoor light at night, such as keeping bedrooms dark and avoiding TVs or personal devices before bed.
While the study can’t prove direct causation—it was observational and involved a mostly white participant group at a single hospital—it does highlight a significant health concern.
The preliminary findings will be presented at the American Heart Association’s Scientific Sessions in New Orleans later this week.
Light Pollution and the Body’s Clock
This isn’t the first time scientists have flagged light pollution as a health hazard.
Prior studies have shown it can keep your heart rate elevated at night and disrupt the circadian rhythm, the body’s natural sleep-wake cycle.
Such disruptions have been linked to coronary artery disease, heart failure, atrial fibrillation, stroke, and other serious cardiovascular conditions.
Coronary heart disease, also known as ischemic heart disease, remains one of the leading causes of death worldwide.
In the UK alone, 2.3 million people are diagnosed, though many more are likely unaware they have the condition.
Lifestyle changes remain the most effective prevention, including a diet rich in fiber, increased activity, and reducing alcohol and tobacco consumption.