Scientists Uncover Link between Nighttime Light and Changes in the Heart

Exposure to light at night has been linked to changes in the structure of the heart and early signs of cardiac dysfunction. Researchers reached this conclusion after analyzing data from more than 11,000 participants in the UK Bio bank project. The study found that people exposed to higher levels of light at night had thicker walls in the left ventricle and weaker heart function. Izvestia reported on how scientists explain this association and what changes they recommend for bedrooms and cities.

The study, led by Professor Lu Qi of Tulane University in New Orleans, was published in the European Heart Journal on September 9. Researchers were investigating a possible link between nighttime light exposure and cardiovascular disease. Previous observations had indicated an increased risk, but there had been insufficient data on the health of the heart muscle itself.

A total of 11,071 people were included in the study. Participants wore a light-sensor device on their wrists for seven days. About three years later, they underwent cardiac magnetic resonance imaging (MRI) to assess the structure and function of their hearts. The researchers then compared the results with the light-exposure data collected earlier.

The nighttime period was determined individually based on the five hours of lowest activity. The analysis took into account exposure to light levels above three lux. This threshold should not be considered a safety standard. The sensors were used to assess the amount of light people were exposed to in their daily lives. However, the study does not establish that the observed differences were caused by any specific source, whether a night-light, television screen or street lamp.

Participants exposed to higher levels of light at night were found to have thicker walls in the left ventricle, one of the heart’s main chambers. Signs of impaired mechanical function of the heart muscle were also observed: during contraction, the heart changed shape less efficiently.

According to the study, participants with recorded exposure to light above three lux had, on average, a 2.4% higher indexed left ventricular mass, 1.5% greater average wall thickness, and a 1.9% lower myocardial contractility index compared with those who had no recorded exposure above three lux.

These changes were also found to affect the right ventricle and left atrium. Thus, the association identified in the study appears to involve multiple chambers of the heart. The authors interpreted the findings as signs of adverse remodeling — a process involving changes in the structure and function of an organ.

According to their explanation, this type of remodeling typically occurs in response to chronic stress or injury. Initially, it can help the body adapt, but over time it may contribute to the weakening of the heart and the development of heart failure.

However, the MRI findings do not necessarily mean that everyone who sleeps with exposure to light at night already has heart disease. Rather, they represent average differences between groups and early changes in individual indicators, whose significance needs to be assessed alongside other health data.