UK Biobank’s research resource is a major contributor in the advancement of modern medicine (Image: Getty)
Exposure to light at night has been linked to significant and potentially harmful changes in the structure and function of the heart. This is according to a new study published in the European Heart Journal last week. The study included 11,071 participants from the UK Biobank, a large-scale biomedical database and research resource containing genetic, lifestyle and health information from half a million UK participants. The database includes blood samples, heart and brain scans and genetic data of the 500,000 volunteer participants.
Participants each wore a light sensor on their wrists for seven days, allowing researchers to measure how much light they were exposed to during the night. Three years later, participants were given a cardiac MRI scan to 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.
They found that people exposed to higher levels of nighttime light had a thicker wall in the left ventricle, one of the heart’s main pumping chambers, the European Society of Cardiology (ESC) said. This thickening reduced the space inside the chamber and was accompanied by 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).
The study concluded: “Greater nighttime light exposure was associated with adverse cardiac remodelling and subclinical functional decline across multiple chambers, statistically mediated by shorter sleep duration. These findings provide potential mechanistic insights into how nighttime light exposure may elevate CVD risk and highlight dark nights and adequate sleep for cardiovascular health.”
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.”
He added: “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.”
Could a darker bedroom help?
The findings were accompanied by an editorial from Professor Thomas Münzel of University Medical Center Mainz, Germany, and colleagues. It 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.”
