LOW levels of light exposure during the nighttime could lead to potentially harmful changes to the structure and function of the heart, according to a new study.
Researchers found in a study of more than 11,000 people that those who slept in lighter environments at night had thicker left ventricle walls and slightly poorer heart muscle contractions. Over a ten year follow up, they were also more likely to develop or die from cardiovascular disease.
The study involved 11,071 UK Biobank participants who each wore an accelerometer on their wrist with an integrated light sensor, which measures light exposure in units of lux, for seven days between 2013 and 2015.
At a three year follow up, they were then given cardiovascular magnetic resonance (CMR) imaging to assess the health of their heart.
People with high nighttime light exposure (above 3 lux) showed small but measurable changes in their hearts and compared with people with no nighttime light exposure, they had 2.4% greater left ventricular muscle mass, 1.5% thicker heart walls and slightly poorer heart muscle contraction (1.9%).
Changes were also seen in the right ventricle and left atrium. The greater the nighttime light exposure, the greater these changes tended to be.
Researchers suggest that shorter periods of sleep appeared to explain around 24 to 49% of these associations, suggesting that disrupted or reduced sleep could be one way nighttime light is linked to heart health. However, the findings suggest that disrupted sleep alone does not explain the whole association.
Starkly, the longer-term follow up results showed associations with much greater risk. When participants were assessed 8 to 10 years after the initial light exposure measurements, people with high nighttime light exposure had a 29% higher risk of heart failure.
They were also found to be at a 24% higher risk of suffering a heart attack, 33% higher risk of stroke, 15% higher risk of atrial fibrillation. Overall, they were at a 26% higher risk of dying from cardiovascular disease, compared with those who had no nighttime light exposure.
However, researchers warned that these are associations and do not prove that nighttime light directly caused the increased risks. Other differences between people with high and low nighttime light exposure could partly explain the findings.
Despite their caution, the researchers still argue that as a first of its kind study, it is strong evidence that night-time light exposure is something that needs further research to confirm a causal link between the associations they observed.
The size of these associations they did find were similar to those reported for other environmental cardiovascular risk factors, such as air pollution and aircraft noise.
Professor Qi, one of the study’s authors, said: “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.”
Professor Thomas Münzel, a cardiologist and environmental health researcher at University Medical Center Mainz, Germany, and colleagues agreed in an editorial accompanying the study, arging that it is time for light pollution to be considered seriously as a health risk and appropriate action taken.
He 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,” he added.
“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.”
Reference
Jin Dai et al. Nighttime light exposure and cardiac structure and function, European Heart Journal. 2026. ehag563
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