News release

From: European Heart Journal

Too much light at night changes the shape and working of the heart

• Light pollution has been linked to cardiovascular disease.
• New study shows that people exposed to too much nighttime light go to develop changes in the shape and function of their hearts.
• Researchers say their findings could help to explain the link between light pollution and heart disease.

Exposure to light during the nighttime is linked to important and potentially harmful changes to the structure and function of the heart, according to a study of more than 11,000 people published in the European Heart Journal [1] today (Thursday).

The research was led by Professor Lu Qi from 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.”

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 structures and functions 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.

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), reducing 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 ventricles and left atria (two other chambers of the heart).

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 [2] Professor Thomas Münzel from University Medical Center Mainz, 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-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.”