Experts have long recommended a dark, light-free bedroom for better sleep. New research shows that sleeping in near-total darkness may carry an added benefit: protecting the heart.
In a study published in the European Heart Journal , researchers at Tulane University’s Celia Scott Weatherhead School of Public Health and Tropical Medicine found that even small amounts of nighttime light exposure were linked to potentially harmful changes in the heart’s structure and function.
“Previous observational studies have linked nighttime light exposure with a higher risk of cardiovascular diseases, but little is known about the related cardiac structure and functional changes,” said lead author Lu Qi , HCA Regents Distinguished Chair and professor at Tulane. “We carried out this research to find out what happens to the heart over time when people are exposed to too much light at nighttime.”
The research team analyzed data from 11,017 participants, all of whom wore a sensor on their wrist for a week to measure levels of light exposure overnight. Some of the participants were exposed to 0 lux (near total darkness) and others were exposed to varying levels of light, with the highest group at more than 3 lux (roughly equivalent to a phone screen at low brightness on a nightstand or a hallway light left on outside a cracked door).
Three years later, each participant was given a cardiovascular magnetic resonance scan to examine any potential changes to the structure and function of their hearts. The results showed participants who were exposed to the highest levels of nighttime light saw the walls of the left chamber of their heart thicken, reducing the space inside the ventricle. There were also signs that the heart’s ability to flex during a heartbeat was reduced — an early indication of heart dysfunction.
“This is the first study of its kind, and it shows that exposure to higher levels of light at nighttime is linked to cardiac remodeling,” Qi said. “This is where the structure and function of the heart changes, and we typically see it in response to chronic stress or injury to the heart. It’s our body’s way of adapting to that stress, but ultimately it weakens the heart and can lead to heart failure.”
Cardiovascular disease, including heart disease and stroke, is the leading cause of death both in the United States and around the world. Nighttime light has been identified as a potential environmental risk factor for this deadly group of diseases. Unlike age or genetics, nighttime light exposure is a modifiable risk factor within most people’s control — simply by turning off screens, drawing curtains before bed or sleeping with an eye mask.
“Light pollution has emerged as a new risk factor for cardiovascular disease,” Qi said. “Our findings, together with evidence from other studies, suggest that a reduction in nighttime light exposure should be considered as one of the potential strategies for preventing heart disease by clinicians and policymakers.”
European Heart Journal
Observational study
People
Nighttime light exposure and cardiac structure and function
10-Sep-2026