Exposure to light at night is associated with structural changes in the heart, indicating that the organ is working harder than usual, according to new research published in the European Heart Journal. These findings support previous research linking nighttime light exposure to an increased risk of cardiovascular issues.
The study utilized data from fitness monitors worn by participants in the UK Biobank, a large collection of health and lifestyle information. These monitors featured light sensors, allowing for objective measurements of light exposure, a feature that distinguishes this study from many prior ones that relied on self-reported data.
Researchers analyzed cardiac MRIs of participants' hearts taken after they had worn the fitness monitors but before any heart problems were diagnosed. Participants were divided into groups based on their nighttime light exposure, with one group experiencing minimal light and the other exposed to at least 3 lux, roughly equivalent to three candles held three feet away. The scans revealed that individuals exposed to light at night had thicker heart walls and reduced pumping efficiency compared to those who slept in darkness.
While these structural changes do not equate to heart disease, they can precede its development. The observed associations align with earlier studies that found correlations between nighttime light exposure and higher risks of stroke, myocardial infarction, and heart failure.
Although the study acknowledges it cannot definitively rule out other unknown factors influencing both heart health and light exposure, the results suggest that light at night may contribute to metabolic and cardiovascular problems. Potential sources of nighttime light exposure include lights within the home, nearby screens such as tablets, or televisions. Researchers recommend maximizing darkness during sleep, a practice also considered a fundamental aspect of sleep hygiene, to potentially benefit heart health.