Proven: Even dim light in the bedroom worsens heart function

A new study published in the European Heart Journal has found that even dim nighttime light (up to 3 lux) from street lamps, alarm clocks, or household appliance indicators causes structural changes in the heart: thickening of the walls, increased myocardial mass, and reduced contractility. Data from 11,071 participants and observations of 70,000 people over 8–10 years confirmed an increased risk of heart failure, stroke, and arrhythmia. Scientists recommend blackout curtains, warm night lights, and stickers over indicators.

A new study published in the European Heart Journal has shown that even dim nighttime light in the bedroom—from street lamps, electronic alarm clocks, household appliance indicators, or smartphones—causes structural changes in the heart and increases the risk of cardiovascular disease. Scientists analyzed data from 11,071 UK residents (average age 61) who wore wrist-mounted light sensors. Participants were divided into groups based on exposure to light brightness up to 3 lux—the threshold at which melatonin production is suppressed. After three years, cardiac MRI revealed signs of chronic overload in the group with the highest nighttime lighting: thickening of the walls, increased heart muscle mass, narrowing of the ventricular cavity, and reduced contractility. The changes affected the left and right ventricles and the left atrium. Although the changes were 1–2%, they are comparable in scale to the effects of air pollution and aircraft noise. Additional monitoring of over 70,000 participants for 8–10 years showed that high nighttime light levels correlate with increased rates of heart failure, stroke, heart attack, atrial fibrillation, and cardiovascular mortality. The mechanism involves not only sleep disruption but also circadian rhythm disruption, increased nervous system activity, and altered stress hormone levels. Bright daylight, in contrast, has almost no effect on the heart. The authors recommend that doctors advise patients on nighttime light levels, close windows with blackout curtains, use only warm-light night lamps, and place opaque stickers over appliance indicators. Darkness is considered an important factor for heart health alongside normal blood pressure and clean air.