Exposure to light at night is linked to potentially dangerous changes in heart structure and function, according to researchers writing in the European Heart Journal.
The study analyzed data from 11,071 participants in the UK Biobank project to evaluate how nocturnal illumination affects overall cardiovascular health.
Volunteers wore wrist-mounted sensors for seven days to continuously monitor night-time light levels in their sleeping environments. Approximately three years later, participants underwent cardiac magnetic resonance imaging scans to measure chamber dimensions, muscle wall thickness, and pumping efficiency.
Cardiac magnetic resonance imaging is considered the gold standard for non-invasive heart evaluation, using powerful magnetic fields to generate high-resolution images of internal soft tissue without radiation. UK Biobank is a major biomedical database in the United Kingdom that collects genetic and lifestyle data across half a million British participants.
Heart scans reveal structural changes
Participants exposed to night-time light levels exceeding three lux showed thickening of the left ventricle wall compared to those sleeping in near-total darkness. Scans also revealed a reduction of internal chamber space inside the left ventricle among the group exposed to higher night light.
A measurement of three lux represents very low illuminance, roughly equivalent to light from a distant streetlight or a television screen filtering into a dark room. The left ventricle is the heart's main pumping chamber, responsible for forcing oxygenated blood into systemic circulation.
When the muscle wall of the left ventricle thickens, the chamber holds less blood and must work harder to contract. Over time, ventricular wall thickening can reduce cardiac elasticity and increase pressure within the heart.
Myocardial deformation refers to how heart muscle fibers stretch and contract during each heartbeat, serving as an early indicator of cardiac muscle strain. Researchers identified signs of a reduced ability of the heart muscle to deform normally during contraction, along with structural alterations in the right ventricle and the left atrium.
Long term cardiovascular risks
In human anatomy, the right ventricle pumps blood to the lungs for oxygenation, while the left atrium receives oxygenated blood returning from pulmonary circulation. Structural changes across multiple heart chambers indicate widespread physiological remodeling in response to night-time light.
Scientists said such cardiac restructurings can occur in response to chronic physical load on the heart tissue. They noted that over time, these structural shifts can contribute to a gradual deterioration in heart performance.
Researchers stated that night-time lighting may be an underestimated risk factor for the cardiovascular system, operating alongside traditional health factors. They suggested that reducing light exposure during sleep represents a potentially simple and accessible way to protect heart health.
The study was published in the European Heart Journal, a peer-reviewed medical publication issued on behalf of the European Society of Cardiology. The findings build on previous investigations into lifestyle factors affecting cardiovascular wellness, such as earlier research demonstrating that shifting routine meal times on weekends away from regular weekday schedules can also increase the risk of heart problems.
