A large-scale study involving more than 11,000 participants has revealed that exposure to light at night is associated with potentially detrimental changes in both the structure and function of the heart. The research was published on September 9 in the European Heart Journal.
The study was led by Professor Lu Qi of Tulane University in New Orleans, USA. He explained: “Earlier observational research has connected nighttime light exposure with an elevated risk of cardiovascular disease, but much remains unknown about the associated changes in cardiac structure and function. We conducted this study to better understand how prolonged exposure to light at night affects the heart over time.”
Tracking Nighttime Light Exposure
The study drew on data from 11,071 participants in the UK Biobank. Each participant wore a light sensor on their wrist for seven days, enabling researchers to quantify the amount of light they encountered during nighttime hours.
Three years after the initial monitoring period, participants underwent cardiac MRI scans. These detailed images allowed scientists to assess both the anatomical structure of the heart and its overall functional capacity.
The researchers then compared those who experienced nighttime light levels exceeding three lux against participants who were exposed to virtually no light at night.
Changes Found Within the Heart
Participants exposed to higher levels of nighttime light exhibited thickening of the left ventricular wall — one of the heart’s main pumping chambers. As the wall thickened, the internal volume of the chamber decreased accordingly.
The scans further indicated that the heart muscle had diminished capacity to flex properly with each heartbeat. Reduced flexibility is widely recognised as an early indicator that the heart may be beginning to operate less efficiently. Similar changes were also observed in the right ventricles and left atria, two additional chambers of the heart.
Professor Qi stated: “This is the first study of its kind, and it demonstrates that exposure to elevated levels of light at night is associated with cardiac remodeling — a process in which the structure and function of the heart alter, typically in response to chronic stress or injury. It is the body’s way of adapting to that stress, but over time it weakens the heart and can contribute to heart failure.”
He added: “Light pollution has emerged as a novel risk factor for cardiovascular disease. Our findings, combined with evidence from other research, suggest that reducing nighttime light exposure should be considered as one of the potential preventive strategies for heart disease by both clinicians and policymakers.”
Could Darker Bedrooms Help Protect the Heart?
The findings were accompanied by an editorial from Professor Thomas Münzel of University Medical Center Mainz, Germany, and colleagues. They argued that physicians should pay greater attention to the amount of light their patients encounter at night, particularly among those already managing existing heart conditions.
They wrote: “It is time for clinicians — especially those treating patients with heart failure or atrial fibrillation — to begin asking about the sleep environment: how dark the bedroom is, whether the patient works night shifts, and how much screen time occurs after sunset. The advice is straightforward and affordable: blackout curtains, warm-coloured bedside lighting, and covering standby LEDs on household electronics. From a public health perspective, the implications are even broader. Light pollution is one of the few environmental hazards that cities can address directly and cost-effectively. Shielded fixtures, warm-spectrum bulbs, and dimming or motion-activated streetlights are already available, energy-efficient, and climate-friendly.”
“Ultimately, this study goes beyond being a mere observation. It establishes a crucial connection between what satellites already reveal — a planet growing ever brighter at night — and the clinical reality unfolding inside our bodies: hearts that are becoming stiffer, weaker, and less efficient. The relationship is biologically coherent, the effect sizes are clinically meaningful, and the dose-response relationship is unambiguous: more light, worse outcomes. The message is clear — darkness deserves recognition as a vital sign, as essential to cardiovascular health as blood pressure management and clean air.”
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