Study Links Nighttime Light Exposure to Cardiac Remodeling

A new analysis of data from the UK Biobank indicates that exposure to low levels of light during sleep can alter the structure and performance of heart muscles, potentially increasing the risk of cardiovascular disease. Participants who slept in environments brighter than 3 lux—approximately the illumination of moonlight or light leaking under a closed door—showed thickening of the left-ventricle wall and reduced flexibility of the heart muscle, early signs of cardiac dysfunction. The changes were observed three years after a week-long monitoring period in which participants wore wrist sensors that recorded nighttime illumination.

"Light pollution has emerged as a new risk factor for cardiovascular disease," said Dr. Lu Qi, senior author of the study and director of the Tulane University Obesity Research Center.

"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 by clinicians and policy makers," Qi added.

The researchers noted that the degree of cardiac remodeling increased with higher light levels, and that between 24% and 49% of the effect could be linked to shorter sleep duration associated with night-time light. Other mechanisms, such as stress or changes in blood pressure, may account for the remaining risk.

Experts not involved in the study cautioned that a single week of wrist-based light measurement may not accurately reflect ocular exposure, and that linking these measurements to heart scans three years later does not establish causality. Further research is needed to confirm the relationship.

To mitigate exposure, health professionals recommend keeping bedrooms as dark as possible—ideally below 1 lux—by using blackout curtains, sealing gaps under doors, and selecting low-intensity, warm-colored night-lights or sleep masks.