How nighttime light exposure impacts your health

In the first study, which was published in JAMA Network Open, researchers analyzed data from almost 89,000 participants who were part of the U.K. Biobank. Between 2013 and 2022, the participants wore light trackers for one week, which recorded over 13 million hours of light exposure. The participants were also monitored for certain health outcomes for an average of nine years.

Overall, the researchers found that participants who slept in the brightest conditions — like sleeping with overhead bedroom lights on — had a 56% higher risk of developing heart failure and a 47% higher risk of having a heart attack. They also had a 32% higher risk of coronary artery disease, a 28% higher risk of stroke, and a 32% higher risk of developing atrial fibrillation (A-fib).

Women had a higher risk of heart failure and coronary artery disease while younger people had a higher risk of heart failure and A-fib.

According to the researchers, the link between sleeping in bright conditions and heart disease was still significant even after accounting for physical activity, smoking status, alcohol intake, diet, shift work, and other potential factors.

"This is the first large-scale study to show that simply being exposed to light at night is a strong and independent risk factor for heart disease," said Daniel Windred, a research associate at Flinders University's FHMRI Sleep Health and the study's lead author.

In a separate study, which has not yet been peer reviewed and will be presented at the American Heart Association's 2025 Scientific Sessions, researchers found that higher levels of artificial light at night were associated with increased stress-related activity in the brain, inflamed arteries, and a greater risk of heart disease.

For the study, researchers analyzed data from 466 adults who had undergone a PET/CT scan at Massachusetts General Hospital between 2005 and 2008. They also measured the amount of nighttime light at each person's home, along with stress signals in the brain and signs of artery inflammation.

Commentary

Previous studies have shown that light's disruption of circadian rhythms can dysregulate different cardiovascular and metabolic processes, including damaging cells in arteries and increasing blood pressure. Circadian disruptions may also contribute to a greater likelihood of blood clotting, which can lead to heart attacks and strokes.

The American Heart Association has also released a scientific statement on the role of circadian health in cardiometabolic health and disease risk. The statement indicates that light pollution is a major factor in disrupting body clocks, can suppress melatonin, delay the onset of sleep, and has been associated with an increased risk of cardiovascular disease, even at low levels.

To avoid these risks, health experts recommend reducing your light exposure at night. Some ways to do this include limiting screen time as much as possible and turning off any unnecessary household lights within four hours of going to sleep.

If turning lights completely off isn't possible, you can use dim or warm lighting. In the bedroom, people should avoid using bright alarm clocks and sleeping near windows. Blackout curtains and a sleep mask can also help reduce light while you sleep.

"We need to take our body clocks seriously," said Sean Cain, a professor at Flinders University and a senior author of the JAMA study. "Protecting our natural sleep rhythms could be a powerful way to fight heart disease."