Key Takeaway:
- Nighttime light exposure was associated with structural and functional heart changes.
- The study found an association, not proof that light directly causes heart disease.
- Experts recommend keeping bedrooms dark and limiting screens and bright light before bed.
Sleeping with even low levels of light was associated with changes in heart structure and function in more than 11,000 adults, according to a study published Sept. 9 in the European Heart Journal, raising concerns about nighttime light exposure as a potential cardiovascular risk factor.
Study links nighttime light to heart changes
Researchers analysed 11,071 UK Biobank participants who wore wrist sensors measuring light exposure for seven days between 2013 and 2015. The participants did not have heart disease at the start of the study and later underwent cardiovascular magnetic resonance imaging about three years afterwards.
Researchers compared participants exposed to more than 3 lux of light at night with those exposed to no nighttime light. Three lux is roughly comparable to moonlight, while 1,000 lux is generally associated with sunlight, according to the study.
People with higher nighttime light exposure had greater left ventricular mass and thicker heart muscle walls, along with a lower ability of the heart muscle to contract. The researchers said these changes may precede conditions including heart failure and atrial fibrillation.
The study was observational, meaning it found an association but could not establish that nighttime light directly caused the cardiac changes. The researchers also noted that participants’ light exposure was measured for only one week and that the sensors could not distinguish specific wavelengths, such as blue light.
“Light pollution has emerged as a new risk factor for cardiovascular disease,” lead researcher Lu Qi, a Tulane University professor, said in a statement. He said reducing nighttime light exposure could be considered among strategies to help prevent heart disease.
Experts urge darker bedrooms
The findings build on earlier research linking nighttime light exposure with cardiovascular health, including studies published in 2025, 2022 and 2024, according to the researchers and accompanying editorial.
Thomas Münzel of the University Medical Centre Mainz in Germany, who wrote the editorial accompanying the study, described measures to reduce nighttime light as “simple and inexpensive.” His recommendations include using blackout curtains, choosing warm-colored bedside lighting when light is needed and covering small indicator lights on electronic devices.
Münzel also said clinicians should consider asking patients about their bedroom environment, including nighttime screen use and how dark the room is. He said the findings support treating bedroom light as a potential cardiovascular risk factor, while emphasising the need for further research.
Sleep experts recommend less screen light
The Sleep Foundation recommends reducing evening exposure to bright light and electronic screens because light can interfere with the body’s sleep-wake cycle. It advises keeping bedroom lighting dim and avoiding screen use before bed when possible.
For people who need light at night, the organisation says warmer-colored lighting may be preferable to cooler light. It also recommends making the bedroom as dark as possible and reducing or eliminating electronic devices in the sleeping environment.
The new findings do not establish that sleeping with a phone screen or other light will cause heart disease. But researchers say the results add to evidence that limiting unnecessary light exposure during sleep may be a practical step worth considering while larger and longer-term studies investigate the connection.
