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Greater exposure to light at night linked to poorer heart health
29% higher risk of heart failure and 33% higher risk of stroke
Even dim light may disrupt the body’s internal clock

Sleeping with the lights on at night may be associated with unfavorable changes in the structure and function of the heart, according to a new study. Researchers found that even relatively dim light—not just a brightly lit bedroom—was associated with thicker heart walls and reduced heart muscle function.

According to the European Heart Journal on September 15, a research team from Tulane University in the United States analyzed the relationship between nighttime light exposure and heart health in 11,071 adults enrolled in the UK Biobank.

Participants wore wrist devices equipped with light sensors for seven days while going about their normal routines. The devices measured how much light they were actually exposed to at night. About three years later, researchers performed cardiac magnetic resonance imaging (MRI) scans to assess the structure and function of their hearts.

The researchers focused on exposure to more than 3 lux of light during nighttime hours. They found that people who were exposed to more nighttime light tended to have less favorable changes in both the structure and function of their hearts.

Compared with people who had very little exposure to light at night, those with higher nighttime light exposure had a 2.4% greater left ventricular mass and an average 1.5% greater thickness of the left ventricular wall. Their myocardial shortening fraction, an indicator of the heart’s ability to contract and pump blood, was 1.9% lower. Unfavorable structural and functional changes were also observed in the right ventricle and left atrium.

The more light people were exposed to at night, the greater the changes in their hearts tended to be. These changes were also associated with shorter sleep duration. Researchers estimated that approximately 24% to 49% of the association between nighttime light exposure and changes in heart structure and function could be explained by reduced sleep duration.

Separately, researchers followed up to 73,286 people to examine whether nighttime light exposure was associated with the actual development of cardiovascular disease. Over approximately 8 to 10 years of follow-up, people with higher nighttime light exposure had a 29% higher risk of heart failure compared with those who had very little exposure to light at night. Their risk of heart attack was 24% higher, stroke 33% higher, and atrial fibrillation 15% higher. The risk of dying from cardiovascular disease was also 26% higher.

One possible explanation for the effects of nighttime light on cardiovascular health is the body’s circadian rhythm. Light is one of the key environmental signals that regulates the body’s internal clock. Exposure to artificial light at night can disrupt melatonin production, sleep, and other circadian processes. Because blood pressure, heart rate, and cardiac metabolism also follow daily rhythms, prolonged exposure to light at night may place additional stress on the cardiovascular system.

However, because this was an observational study, the researchers cannot conclude that sleeping with the lights on directly causes changes in heart structure. Most participants were also White, and nighttime light exposure was measured for only seven days, which are additional limitations of the study.

The researchers said that greater nighttime light exposure was associated with unfavorable structural changes and potential declines in function across several areas of the heart, with some of these associations linked to shorter sleep duration. The findings suggest that sleeping in a dark environment and getting sufficient sleep may be important for cardiovascular health.

Source: 매일경제 (https://www.mk.co.kr/news/it/12152915)