Exposure to light during the night is associated with potentially harmful changes in the structure and function of the heart, according to research published in the European Society of Cardiology’s European Heart Journal.
The findings indicate that people exposed to higher levels of light while sleeping showed thickening of the heart’s left ventricular wall and signs of reduced cardiac function. However, researchers stressed that the observational study cannot establish a direct causal relationship.
Light exposure monitored overnight
The study, led by Tulane University in New Orleans, involved 11,071 participants from the UK Biobank database.
Each participant wore a light sensor on their wrist for seven days to record nighttime light levels. Three years later, they underwent cardiac magnetic resonance imaging, allowing researchers to examine the heart’s structure and function in detail.
Researchers compared people exposed to more than three lux during the night with those exposed to almost no light. A lux is a unit measuring the intensity of light reaching a surface as perceived by the human eye.
Changes detected in the heart
People with greater exposure to nighttime light showed thickening of the wall of the heart’s left ventricle, reducing the space inside it.
There were also signs that the heart muscle’s ability to relax and expand during a heartbeat had declined, which can be an early indication of impaired cardiac function. Changes were also identified in the right ventricle and left atrium.
“This is the first study of its kind and shows that exposure to higher levels of light during the night is associated with cardiac remodelling, meaning that the structure and function of the heart change,” said lead researcher Lu Qi, a professor at Tulane University.
“This is usually observed in response to chronic stress or injury to the heart and is the body’s way of adapting to that stress. However, it ultimately weakens the heart and may lead to heart failure.”
Doctors urged to consider sleep environments
In an accompanying editorial, Professor Thomas Münzel of Mainz University Medical Centre in Germany and his colleagues said doctors, particularly those treating patients with heart failure or atrial fibrillation, should consider their patients’ sleeping environments.
Factors include how dark the bedroom is, whether the patient works night shifts and how much they use screens after sunset.
The authors recommended several simple and inexpensive measures, including blackout curtains, bedside lighting in warm tones and covering small standby LED lights on electronic devices.
Wider impact of light pollution
The editorial also highlighted the broader public health implications of light pollution, describing it as an environmental risk that cities can address directly and at relatively low cost.
Appropriate urban lighting, warm-coloured bulbs and street lights with adjustable brightness or motion activation are already available, energy efficient and climate friendly.
Study limitations
The authors identified several limitations. The sensor measured only brightness and not the colour spectrum of the light, which is important to the body’s biological clock.
Participants were monitored for only one week and were predominantly white and healthier than the general population.
As an observational study, the research cannot prove that nighttime light exposure directly caused the changes detected in the heart.
Source: AMNA
