EHJ: Scientists Find That Sleeping in Complete Darkness May Benefit Heart Health

Scientists in Germany have found that regular exposure to light during sleep is associated with changes in the structure and function of the heart that may increase the risk of heart failure, heart attack, and stroke. The findings were published in the European Heart Journal (EHJ).

The researchers analyzed data from 11,071 participants in the UK Biobank who wore light and motion sensors for one week and underwent cardiac MRI several years later. People exposed to the highest levels of nighttime light had, on average, a left ventricle that was 2.4% larger, a heart wall that was 1.5% thicker, and 1.9% lower contractile function compared with those who slept in the darkest conditions.

These changes may be linked to so-called cardiac remodeling — structural changes in the heart that accompany the development of cardiovascular disease. At the same time, nearly half of the observed changes could be explained by insufficient sleep.

“Another possible mechanism is disruption of circadian rhythms. Light at night can affect the body’s internal biological clock, which regulates not only sleep but also blood pressure, hormone levels, and inflammatory processes,” the scientists explained.

The association was also observed with cardiovascular diseases. Over the 10-year follow-up period, participants exposed to the highest levels of nighttime light had a 29% higher risk of heart failure, a 24% higher risk of heart attack, a 33% higher risk of stroke, and a 26% higher risk of death from cardiovascular disease compared with people who slept in the darkest conditions.

The researchers noted that light exposure was measured for only one week and that the spectrum of the light was not assessed. Nevertheless, they believe that reducing exposure to light at night may benefit heart health through simple measures such as using blackout curtains, avoiding bright light sources in the bedroom, and covering illuminated indicators on household appliances.