Hearts after Dark Too Much Light at Night Changes the Shape and Working of the Heart

Brighter nights may be linked to more than disrupted sleep. A study of over 11,000 adults found an association between nighttime light exposure and differences in heart structure and function, although it does not establish cause and effect.

Exposure to light at night is associated with potentially harmful differences in heart structure and function, according to a study of more than 11,000 people published in the European Heart Journal. The observational findings do not establish that nighttime light exposure caused these differences.

The research was led by Professor Lu Qi of Tulane University in 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.”

The study included 11,071 UK Biobank participants who wore wrist-mounted light sensors for seven days to measure their nighttime exposure. Three years later, they underwent cardiac MRI scans to assess heart structure and function.

Researchers compared participants exposed to nighttime light levels above three lux with those exposed to almost no light.

Higher exposure was associated with thicker walls in the left ventricle, one of the heart’s pumping chambers, and a smaller chamber cavity. The researchers also found signs of reduced heart muscle deformation during a heartbeat, an early indicator of impaired function, alongside differences in the right ventricle and left atrium.

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 remodelling. 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.”

In an accompanying editorial, Professor Thomas Münzel of University Medical Center Mainz, Germany, and colleagues called for greater attention to nighttime light exposure in clinical practice and public policy.

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.”

Original Article: Nighttime light exposure and cardiac structure and function; European Heart Journal; DOI:10.1093/eurheartj/ehag563

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