Even low level night-time light may weaken the heart
HEALTH/LIFESTYLE
A dark, light-free bedroom has long been recommended for better sleep. Now, 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 night-time light exposure were linked to potentially harmful changes in the heart’s structure and function.
“Previous observational studies have linked night-time light exposure with a higher risk of cardiovascular diseases, but little is known about the related cardiac structure and functional changes,” says 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 night-time.”
The research team analysed 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 were exposed to 0 lux (near total darkness) while 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 door that is ajar.
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. Those who were exposed to the highest levels of night-time 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 night time is linked to cardiac remodelling,” Qi says. “This is where the structure and function of the heart change, 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 around the world. Night-time light has been identified as a potential environmental risk factor. Unlike age or genetics, night-time light exposure is something people can do something about — simply by turning off screens; covering up any standby lights and digital clock displays; turning off anything that might spill light into a bedroom; and drawing curtains before bed or sleeping with an eye mask.
“Our findings, together with evidence from other studies, suggest that a reduction in night-time light exposure should be considered as one of the potential strategies for preventing heart disease by clinicians and policymakers,” Qi adds.
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