Exposure to light at night may be linked to potentially harmful changes in the heart’s structure and performance, according to a study involving more than 11,000 people. The findings were published in the European Heart Journal on September 9.
The research was led by Professor Lu Qi of Tulane University, New Orleans, USA. He said: “Previous observational studies have linked nighttime light exposure with a higher risk of cardiovascular disease, but little is known about the related cardiac structure and 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 nighttime.”
Measuring Nighttime Light Exposure
The study included 11,071 participants from the UK Biobank. Each person wore a light sensor on the wrist for seven days so researchers could measure how much light they were exposed to at night.
Three years later, the participants underwent cardiac MRI scans. These detailed scans allowed researchers to examine both the structure of the heart and how effectively it was functioning.
The team compared people exposed to more than three lux of nighttime light with those exposed to almost no light at night. Lux is a measure of how much visible light reaches a surface.
Changes in Multiple Heart Chambers
People with higher nighttime light exposure showed thickening in the wall of the left ventricle (one of the chambers of the heart). That thickening reduced the amount of space available inside the chamber.
Researchers also found evidence that the heart muscle was less able to flex properly during each heartbeat. Reduced flexibility can be an early sign that the heart is not functioning normally.
Changes were also observed in the right ventricles and left atria (two other chambers of the heart), suggesting that the association was not limited to a single part of the organ.
Professor Qi said: “This is the first study of its kind, and it shows that exposure to higher levels of light at nighttime is linked to cardiac remodeling. This is where the structure and function of the heart changes and we typically see it in response to chronic stress or injury to the heart. It’s our body’s way of adapting to that stress, but ultimately it 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 reduction of nighttime light exposure should be considered as one of the potential strategies for preventing heart disease by clinicians and policy makers.”
Could a Darker Bedroom Help Protect the Heart?
In an accompanying editorial, Professor Thomas Münzel from University Medical Center Mainz, Germany, and colleagues argued that doctors should pay more attention to patients’ nighttime light environments.
They said: “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. The advice is simple and inexpensive: blackout curtains, warm-coloured bedside lighting, and covering the small standby LEDs on household electronics. From a public health perspective, the implications are larger still. Light pollution is one of the few environmental hazards that cities can control directly and affordably. Shielded fixtures, warm-spectrum bulbs, and dimming or motion-activated streetlights are already available, energy-efficient, and climate-friendly.
“Ultimately, this study is more than an interesting observation. It provides a crucial link between what satellites already show us, i.e., a planet glowing ever brighter at night, and the clinical reality unfolding inside our chests: hearts that are becoming stiffer, weaker, and less efficient. The relationship is biologically coherent, the effect sizes are clinically meaningful, and the dose–response is unambiguous: more light, worse outcomes. The takeaway is clear: darkness deserves recognition as a vital sign, as essential to cardiovascular health as blood pressure control and clean air.”
References:
“Nighttime light exposure and cardiac structure and function” by Jin Dai, Wen Dai, Yoriko Heianza and Lu Qi, 9 September 2026, European Heart Journal.
DOI: 10.1093/eurheartj/ehag563
“The dark night as a cardiovascular vital sign: personal light exposure, subclinical cardiac remodelling, and the urban exposome” by Thomas Münzel, Marin Kuntic and Andreas Daiber, 9 September 2026, European Heart Journal.
DOI: 10.1093/eurheartj/ehag650
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