Sleeping with a Light on Could Affect Your Heart, New Study Finds

Even light as faint as moonlight or the glow under a door may matter more than you think. Here’s what doctors say could be happening inside your body while you sleep.

The preference for sleeping with a light on or off varies for every individual. Some prefer wearing an eye mask or drawing blackout curtains for a completely light-free sleep. Others may find it more comforting to sleep with a little light on. A new study has found a link between the nighttime light in your bedroom and your heart.

The research, published in the European Heart Journal in September 2026, analyzed data from 11,071 U.K. Biobank participants who were made to wear a light sensor on their wrist for seven days to measure how much light reached them while asleep at night. After three years, each participant underwent cardiac MRI scans so researchers could check the structure and function of their hearts.

Researchers then compared the MRI scans of those exposed to more than three lux of light at night, which is about as bright as moonlight or the glow slipping in under a door, with those who slept in near-total darkness.

The scans showed people who were more exposed to more light at night had a thicker wall in the heart’s left ventricle, leaving less room inside the chamber. Their heart muscle also showed early signs that it wasn’t functioning as efficiently as it should, as it was less flexible with each heartbeat.

The researchers of the study concluded that “nighttime light exposure may elevate cardiovascular disease risk and highlight dark nights and adequate sleep for cardiovascular health.”

In 2025, another study presented at the American Heart Association’s Scientific Sessions also found a link between nighttime light and the heart. The study showed that people who were exposed to artificial light at night had higher brain stress activity, inflamed blood vessels, and a slightly higher risk of cardiovascular events, including heart disease. There were also findings that sleeping with a light on may raise the heart rate and the risk of high blood pressure in some groups.

Sleep medicine specialist Christopher Winter, MD, shed more light on the possible reasons behind the link between sleeping with the light on and the heart. “The brain understands light as a signal to wake up,” he told Women’s Health. “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.”

According to the Sleep Foundation, the presence of light, especially blue light from screens, LEDs, and fluorescent bulbs, may also affect the body’s production of melatonin, which is the hormone that helps induce sleep.

Light at night may disrupt the body’s circadian rhythm, or body clock, according to Yu-Ming Ni, MD, a cardiologist and lipidologist. This rhythm helps in regulating sleep, blood pressure, metabolism, and other processes that may affect the heart’s health.

“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. Ni told Women’s Health. “When sleep is consistently disrupted or inadequate, those processes can be affected, potentially increasing cardiovascular stress over time”

While these studies may appear alarming, especially to those who sleep with a light on, experts note that the research shows a link and not proof that light causes heart problems.

To be safe, you can try sleeping with a mask or dimmer lights in the evening and limiting screen time at night before bed. Sleep Foundation also suggests using a dim, warm-colored light or red light if you can’t sleep in total darkness because red light does not disturb the body’s internal clock.

As Dr. Ni puts it, “The goal isn’t to create perfect darkness at all costs, but to minimize unnecessary light and make your sleep environment as comfortable and conducive to sleep as possible.”