Sleeping in a room with as little as 3 lux of light can alter the structure and function of the heart, potentially increasing the risk of serious cardiovascular issues, according to a recent study. This level of light is comparable to moonlight or light seeping under a closed door.
Researchers found that individuals who slept in rooms with 3 lux or more of light exhibited thickening of the left ventricle, the heart's primary pumping chamber. This condition, known as left ventricular hypertrophy, can impair the heart's ability to fill and pump blood effectively. The study also indicated that the heart's contraction and pumping efficiency were reduced in individuals exposed to more light during sleep.
These changes are associated with chronic stress or injury to the heart, ultimately weakening it and potentially leading to heart failure, irregular heart rhythms, reduced blood flow, and cardiac arrest. "It is time for clinicians, particularly those managing patients with heart failure or atrial fibrillation, to start asking about the sleep environment: how dark the bedroom is, whether the patient works night shifts, and how much screen use occurs after sunset," said Thomas Münzel from University Medical Center Mainz, Germany, one of the study's authors.
The study compared individuals sleeping in brightly lit rooms to those sleeping in near darkness. While the exact mechanism by which nighttime light affects the heart is still under investigation, researchers hypothesize that light exposure may disrupt the body's natural circadian rhythm. Even though eyelids block most light, some light can still penetrate and affect internal bodily processes.
Experts suggest that simple and affordable solutions can mitigate this risk. These include using blackout curtains, opting for warm-colored bedside lighting, and covering small LED indicator lights on electronic devices. Sleep masks are also recommended for those unable to completely darken their bedrooms.
From a public health perspective, addressing light pollution is seen as a significant opportunity. Münzel noted that controllable and cost-effective measures, such as shielded light fixtures, warm-spectrum bulbs, and dimming or motion-activated streetlights, are readily available and can contribute to energy efficiency and climate-friendly urban environments.