There are a few universal truths with sleep: Most people should aim to get at least seven hours of sleep a night, and you'll want to snooze in a cool, dark room. But that last part may have benefits that extend beyond your ability to log enough sleep at night, according to new research published in European Heart Journal. The study found a link between nighttime light exposure—think: night lights, hallway lights, and street lights outside your window—and a higher risk of developing factors that could raise your odds of heart disease.
It's a stretch to say that you're doomed to develop heart disease if you live and sleep in a busy city environment, but doctors say the findings make the case for doing whatever you can do to block out light at night. Meet the experts: Christopher Winter, MD, a sleep medicine specialist, neurologist, and author of The Sleep Solution: Why Your Sleep Is Broken and How to Fix It; Yu-Ming Ni, MD, cardiologist and lipidologist at MemorialCare Heart and Vascular Institute at Orange Coast Medical Center in Fountain Valley, CA For the study, researchers analyzed data from 11,071 people who participated in the UK Biobank, a large-scale biomedical database. Participants wore a light sensor on their wrist for seven days, which measured how much light they were exposed to during the night.
After three years, the participants were asked to do cardiac MRI scans to look at the structure and function of the heart. The researchers then broke participants into two groups: Those who were exposed to nighttime light levels above three lux (similar to bright moonlight or light that seeps under a door) and those who were exposed to almost no light at night. The researchers found that those who were exposed to at least three lux of nighttime light had thickening in the wall of the left ventricle chamber of the heart, reducing the space inside the chamber.
The MRI scans also found that the heart muscle was less flexible during each heartbeat, which can be an early sign that the heart isn't functioning as efficiently as it should. The researchers concluded that "nighttime light exposure may elevate cardiovascular disease risk and highlight dark nights and adequate sleep for cardiovascular health." This isn't the first study to link light exposure at night to heart issues. Research presented at the American Heart Association's Scientific Sessions 2025 found that people who were exposed to higher levels of artificial light at night had higher brain stress activity, blood vessel inflammation, and a slightly higher risk of major heart events, including heart disease.
There could be a few things going on, according to doctors. "The brain understands light as a signal to wake up," says Christopher Winter, MD, a sleep medicine specialist, neurologist, and author of The Sleep Solution: Why Your Sleep Is Broken and How to Fix It. "Light at night creates a conflict between a brain that wants to sleep and a brain getting a signal that the timing is off for that sleep." That may interfere with the body's circadian rhythm, which helps to regulate sleep, blood pressure, metabolism, and other processes that affect cardiovascular health, according to Yu-Ming Ni, MD, cardiologist and lipidologist at MemorialCare Heart and Vascular Institute at Orange Coast Medical Center in Fountain Valley, CA.
"Over time, poor sleep and circadian disruption may contribute to cardiovascular risk factors such as high blood pressure, obesity, and diabetes," he says. Sleep is also an important time for the cardiovascular system to recover: "During healthy sleep, heart rate and blood pressure generally decrease, giving the heart and blood vessels a chance to recover from the demands of the day," Dr. "When sleep is consistently disrupted or inadequate, those processes can be affected, potentially increasing cardiovascular stress over time." But experts stress that the study found a link between nighttime light exposure and a higher risk of heart disease risk factors—it didn't prove that one caused the other.
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