Scientists have proposed a hypothesis based on a study suggesting that bedroom lighting at night may influence the heart. This conclusion was drawn after examining sleep patterns of 10,000 people, with the results published in the European Heart Journal.
The study demonstrated that individuals who slept under low light had a higher likelihood of experiencing enlarged heart chambers and thicker walls compared to those who slept in near-total darkness. This condition could potentially lead to heart failure.
In the group exposed to the most light, participants were kept under illumination of 3 lux for about 34 minutes daily. This is a very low level of light, comparable to bright moonlight or dim light. According to new data in the European Heart Journal, even such weak illumination can affect the heart.
For those who slept under this level of light for the longest duration, the heart walls were 1.5% thicker than those who slept in the dark. Furthermore, the left ventricle size was 2.4% larger, and the heart's contractile ability decreased by 1.9%.
Pathomorphologist Lu Chi from Tulane University in the USA noted that this is the first such study indicating a link between increased nighttime light exposure and changes in heart structure. These changes affect both the structure and function of the heart, which is typically associated with prolonged mental stress. This can weaken the heart and trigger heart failure.
The study also showed that for people sleeping under light, the risk of heart failure over 8–10 years increased by 29%, the risk of atrial fibrillation increased by 15%, and the risk of myocardial infarction increased by 24%. No significant link was found between sleeping under bright daylight and cardiovascular death.
The journal BMJ reported that nighttime illumination, whether from an on light, mobile screen, nightlight, or streetlamp, affects heart function—a process known as cardiac remodeling. Light enters the brain through the eyes, disrupting the body's internal circadian rhythms. Due to the light, the brain cannot fully relax, which can lead to an increased heart rate even during sleep, and all of this directly impacts the heart.