Nighttime Light Exposure Linked to Heart Structure Changes in New Study

A new study published in the European Heart Journal suggests that even low levels of light exposure during sleep can lead to measurable changes in heart structure, beyond just affecting sleep quality. The research involved 11,071 participants who wore a light sensor for seven days to record ambient light levels. Approximately three years later, these individuals underwent cardiac MRI scans to assess heart structure and function.

The study compared participants exposed to more than three lux of light at night with those sleeping in near-total darkness. Three lux is equivalent to a dim phone screen or a lit hallway light, levels most people would consider dark. The group exposed to higher light levels showed a 2.4% increase in left ventricular mass, a 1.5% increase in wall thickness, and a 1.9% decrease in heart muscle contraction efficiency. These changes indicate a thicker heart wall, smaller chamber, and reduced flexibility, patterns typically associated with a heart under prolonged strain.

Researchers, including lead author Prof. Lu Qi from Tulane University, noted that part of this effect might be mediated by sleep deprivation caused by light exposure, rather than solely by the light itself. Prof. Thomas Münzel from the University Medical Center Mainz highlighted that while the absolute effect sizes are modest, they are consistent, dose-dependent, and observed across all heart chambers, strengthening the evidence for a genuine link.

Further analysis of over 73,000 participants tracked for eight to ten years revealed that higher nighttime light exposure was associated with a 29% increased risk of heart failure, a 24% increased risk of heart attack, a 33% increased risk of stroke, and a 26% increased risk of death from cardiovascular diseases.

The study's findings are particularly relevant for Israel, described as one of the most light-polluted countries relative to its size, with most of its population in dense urban areas. The researchers suggest simple, accessible solutions like blackout curtains, turning off hallway lights, covering device indicator lights, and removing phones from bedrooms to mitigate these risks. While the study is observational and cannot definitively prove causation, the researchers acknowledge potential confounding factors like urban living or socioeconomic status, and the light measurement was taken over only one week.