More light at night linked to changes in heart structure and function

by European Society of Cardiology

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Exposure to light at night is linked to important and potentially harmful changes in the structure and function of the heart, according to a study of more than 11,000 people published in the European Heart Journal on Thursday.

The research was led by Professor Lu Qi from Tulane University in New Orleans. 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 structural 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 night."

The research included 11,071 people who are part of the UK Biobank study. All participants wore a light sensor on their wrists for seven days to measure light levels overnight. Three years later, participants were given a cardiac MRI scan to carefully examine the structure and function of the heart.

Researchers compared people who were exposed to light levels of more than three lux with people exposed to almost no light at night.

Signs of strain in the heart

This showed that people with high exposure to nighttime light had thickening of the wall of the left ventricle (one of the chambers of the heart), which reduced the space inside the chamber. There were signs that the heart muscle's ability to flex during a heartbeat was reduced. This is an early indicator of heart dysfunction. Researchers also found changes in the right ventricle and left atrium (two other chambers of the heart).

Qi said, "This is the first study of its kind, and it 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 change, 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 reducing nighttime light exposure should be considered one of the potential strategies for preventing heart disease by clinicians and policymakers."

From bedrooms to city streets

In an accompanying editorial, Professor Thomas Münzel from University Medical Center Mainz in Germany and colleagues 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-colored 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."

Publication details

Nighttime light exposure and cardiac structure and function, European Heart Journal (2026). DOI: 10.1093/eurheartj/ehag563

Journal information: European Heart Journal

Clinical categories

CardiologySleep & RecoveryHealthy living Provided by European Society of Cardiology Who's behind this story?

Gaby Clark

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