A new study from Flinders University has found that being exposed to bright light at night can raise your risk of serious heart problems—including heart attacks, strokes, and heart failure.
This large-scale study is the first of its kind to show that light at night is a strong and independent risk factor for heart disease.
The research was published in JAMA Network Open and used data from almost 89,000 people in the UK. Scientists tracked over 13 million hours of light exposure using wrist sensors and followed participants for up to 9.5 years.
What they found was eye-opening.
People exposed to the brightest light at night had a 56% higher chance of developing heart failure and a 47% higher risk of having a heart attack, even after accounting for other important factors like exercise, diet, sleep habits, and genetics.
Dr. Daniel Windred, the study’s lead author and a researcher at Flinders University’s FHMRI Sleep Health group, said this is a health risk that most people don’t think about—but it’s something we can easily control.
He explained that being exposed to light at night throws off the body’s internal clock, also known as the circadian rhythm. This clock helps regulate many functions in the body, including sleep and heart health.
“When you stay up late with bright lights or screens on, it confuses your body into thinking it’s still daytime,” says Dr. Windred. “This can disturb your sleep and raise your risk of dangerous heart conditions over time.”
The good news is there are simple things you can do to lower this risk. Using blackout curtains, dimming indoor lights in the evening, and turning off screens an hour before bed can all help keep your body clock on track.
The study also found that women and younger people are especially sensitive to the effects of light at night. Professor Sean Cain, one of the senior researchers, pointed out that women in the study who were exposed to high night light had heart failure risks similar to men—which is unusual because women usually have some natural protection against heart disease.
Associate Professor Andrew Phillips, another senior author, added that this problem isn’t just limited to shift workers or people living in brightly lit cities. Everyday habits like checking your phone in bed, falling asleep with the TV on, or leaving your bedroom lights on can expose you to harmful levels of light.
Most earlier studies looked at light exposure using satellite images or surveys, but this study used real-time data from wearable devices, giving researchers a much clearer view of how indoor light affects health.
Heart disease is still the number one cause of death around the world. This research shows that it’s time to take nighttime light exposure just as seriously as we do smoking, poor diet, or not getting enough exercise.
The team behind the study is now calling for more research to help set lighting guidelines for homes, hospitals, and public spaces. “We need to take our body clocks seriously,” says Professor Cain. “Protecting our natural sleep rhythms might be a powerful way to lower the risk of heart disease.”
If you care about heart health, please read studies about blood thinners that may not prevent stroke in people with heartbeat problems and this diabetes drug may protect heart health in older veterans.
For more about heart health, please read studies about why light-to-moderate drinking is linked to better heart health and reconsidering the long-term use of high blood pressure beta blockers after a heart attack.
The study is published in JAMA Network Open.
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