Sleeping with even minimal light exposure may significantly increase the risk of developing heart disease, according to new research. The study suggests that light pollution in the bedroom can lead to structural changes in the heart, forcing it to work harder and increasing the likelihood of heart attack, stroke, and rhythm disorders.
Researchers from Tulane University analyzed the sleep patterns and light exposure of over 11,000 adults who did not have pre-existing heart conditions. Participants wore wrist sensors for a week to measure ambient light levels during sleep. Three years later, MRI scans revealed that individuals exposed to more than three lux of light—comparable to bright moonlight—had thicker walls in their left ventricle.
The left ventricle is critical for circulating oxygenated blood throughout the body. When its walls thicken, the chamber shrinks, making it more difficult for the heart to pump effectively. This structural change, known as 'cardiac remodeling,' can impair the heart's ability to beat efficiently and maintain blood pressure.
Approximately 25% of the study participants experienced no nighttime light exposure above three lux. The study found that the extent of cardiac damage correlated with the intensity of light exposure. Common sources of light include smartphone screens, digital alarm clocks, and external streetlights.
Researchers estimate that between 24% and 49% of the observed impact on the heart was also linked to shorter sleep durations, averaging five to six hours per night. This reduced sleep is considered a direct consequence of nighttime light exposure.
Dr. Lu Qi, senior study author and director of the Tulane University Obesity Research Center, stated that light pollution has emerged as a novel risk factor for cardiovascular disease. He suggested that reducing nighttime light exposure should be considered by healthcare professionals and policymakers as a potential strategy for preventing heart disease.
Heart disease is the leading cause of death in the United States, with nearly one million Americans dying from it annually. The findings, published in the European Heart Journal, were based on data from the UK Biobank, involving 11,017 participants aged 40 to 69. The average participant age was 61, and 57% were women, with 98% identifying as white.
Participants underwent heart MRI scans approximately three years after the initial monitoring period. The scans showed that those exposed to at least three lux at night had larger cardiac chamber volumes in their left and right ventricles, as well as the left atrium. Furthermore, increased wall mass and thickness were observed in the left ventricle, along with greater strain in this area.
The study acknowledged limitations, including measuring light exposure for only one week via wrist sensors rather than directly on the eyes. The researchers recommend minimizing nighttime light exposure to below one lux, suggesting practical measures like using blackout curtains and turning off lights that might seep into the bedroom.