A study involving more than 11,000 people found that light exposure at night is associated with potentially harmful changes in both the structure and function of the heart. The findings were published on September 9 in the European Heart Magazine.
The research was led by Professor Lu Qi from Tulane University, New Orleans, USA. He said: “Previous observational studies have linked nighttime light exposure to an increased risk of cardiovascular disease, but little is known about heart structure and related functional changes. We carried out this research to find out what happens to the heart over time when people are exposed to too much light at night.”
Tracking Night Light Exposure
The study included 11,071 participants from the UK Biobank. Each person wore a light sensor on their wrist for seven days, allowing researchers to measure how much light they were exposed to during the night.
Three years later, the participants underwent cardiac MRIs. These detailed images allowed scientists to examine the structure of the heart and its effectiveness.
The researchers then compared participants who experienced nighttime light levels greater than three lux to those who were exposed to almost no light at night.
Changes found within the heart
People exposed to higher levels of light at night showed thickening in the wall of the left ventricle (one of the chambers of the heart). As the wall became thicker, the amount of space inside the chamber was reduced.
The scans also revealed signs that the heart muscle was less able to flex normally during each heartbeat. Reduced flexibility may be an early sign that the heart is starting to work less efficiently. Changes were also detected in the right ventricles and left atria (two other chambers of the heart).
Professor Qi said: “This is the first study of its kind and shows that exposure to higher levels of light at night is linked to cardiac remodeling. This is where the structure and function of the heart changes, and we typically see this in response to chronic stress or injury to the heart. “It’s our body’s way of adapting to that stress, but it ultimately weakens the heart and can lead to heart failure.
“Light pollution has emerged as a new risk factor for cardiovascular disease. Our findings, together with evidence from other studies, suggest that clinicians and policy makers should consider reducing nighttime light exposure as one of the potential strategies to prevent heart disease.”
Could darker bedrooms help protect the heart?
The findings were accompanied by an editorial by Professor Thomas Münzel of the University Medical Center Mainz, Germany, and colleagues. They argued that doctors may need to pay more attention to the amount of light their patients encounter at night, particularly among people who already have certain heart conditions.
They said: “It’s time for doctors, particularly those caring for 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 dusk. The advice is simple and inexpensive: blackout curtains, warm-colored lighting on bedside tables, and covering small standby LEDs on home electronics. From a public health perspective, the implications are still Light pollution is one of the few environmental hazards that cities can control directly and affordably, with energy-efficient and climate-friendly shielded luminaires, warm-spectrum bulbs, and dimmable or motion-activated streetlights now available.
“Ultimately, this study is more than an interesting observation. It provides a crucial link between what satellites already show us, namely a planet that gets brighter and brighter at night, and the clinical reality unfolding inside our chests: hearts that are becoming stiffer, weaker, and less efficient. The relationship is biologically consistent, the effect sizes are clinically significant, and the dose-response is unambiguous: more light, worse outcomes. The conclusion is clear, darkness deserves recognition as a sign vital, as essential for cardiovascular health such as blood pressure control and clean air.