European Heart Journal: Nighttime light exposure may alter heart structure

Exposure to light at night is associated with changes in the structure and function of the heart that could potentially increase the risk of cardiac dysfunction, according to a study involving more than 11,000 people. The study was published in the European Heart Journal.

The research was conducted by a team led by Professor Lu Qi of Tulane University in New Orleans. The scientists used data from 11,071 participants in the UK Biobank. All of them wore a wrist-worn sensor for seven days that measured their exposure to light at night. Three years later, the participants underwent cardiac magnetic resonance imaging (MRI) to assess the structure and function of their hearts.

The researchers compared people exposed at night to light levels above three lux with those who were in almost complete darkness. Participants in the first group had thickening of the wall of the left ventricle, one of the heart’s main chambers. This reduced the ventricle’s internal space. In addition, there were signs of a reduced ability of the heart muscle to relax and stretch during the cardiac cycle, which may be an early sign of impaired function.

Changes were also detected in the right ventricle and left atrium. According to Lu Qi, the combination of these changes points to what is known as cardiac remodeling — a restructuring of the heart’s structure and function that typically occurs in response to prolonged stress or damage. Over time, such changes can weaken the heart and contribute to the development of heart failure.

At the same time, the study demonstrates an association between nighttime light exposure and changes in the heart, but does not by itself prove that light directly causes these abnormalities.

The authors believe that reducing exposure to light at night could become one way of preventing cardiovascular disease. In an accompanying editorial, Professor Thomas Münzel of the University Medical Center Mainz and his colleagues urged physicians to pay attention to patients’ sleeping conditions — how dark their bedrooms are, whether they work at night, and whether they use screens after dark.

Experts recommend simple measures such as using blackout curtains, choosing warm and less bright light near the bed, and turning off or covering small LED indicator lights on household appliances. At the city level, the authors note, light pollution can be reduced through the use of shielded lighting fixtures, warm-spectrum lamps, and street lighting that automatically dims or switches on only when necessary.

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