Study Links Low-Level Nighttime Light to Heart Muscle Changes
Research involving over 11,000 participants found that sleeping in environments brighter than 3 lux is associated with thickening of heart muscle walls and reduced cardiac function, suggesting nighttime light exposure may be a modifiable risk factor for cardiovascular disease.
A new analysis of data from the UK Biobank indicates that exposure to low levels of light while sleeping can alter the structure and performance of the heart. Participants who slept in conditions exceeding 3 lux – roughly the brightness of moonlight leaking through a closed door – showed thickening of the left-ventricle wall and a decrease in the chamber’s capacity to fill and contract, early signs of cardiac remodeling.
The study tracked more than 11,000 adults without prior cardiovascular disease using wrist-worn sensors for a week to record nighttime illumination. Three years later, each participant underwent cardiovascular magnetic resonance imaging. Compared with those who slept in complete darkness, individuals exposed to higher light levels exhibited measurable changes in multiple heart chambers.
"Light pollution has emerged as a new risk factor for cardiovascular disease," said Dr. Lu Qi, senior author and professor at Tulane University.
"Our findings, together with evidence from other studies, suggest that reduction of nighttime light exposure should be considered as one of the potential strategies for preventing heart disease," Qi added.
Researchers estimated that between a quarter and half of the observed heart changes could be linked to shorter sleep duration associated with brighter environments, while the remainder may involve stress, blood-pressure shifts, and other physiological responses.
Cardiovascular experts not involved in the work cautioned that the observational design does not prove causality. Karl Lawrence of King’s College London noted that a single week of wrist-based light measurement may not accurately reflect ocular exposure and that linking these data to heart scans taken three years later requires further investigation.
The authors recommend practical steps to minimize bedroom illumination, such as using blackout curtains, sealing gaps under doors, employing low-color-temperature night-lights, or wearing a sleep mask, to help maintain optimal sleep quality and potentially protect heart health.