Light is an important cue that helps set the body's internal 24-hour clock and establish its circadian rhythms. Because they regulate biological processes such as sleep, wakefulness, digestion and hormone release, disrupting circadian rhythms can affect cardiovascular health.

Studies have shown that by interfering with the quality and quantity of sleep, exposure to artificial light at night increases the risk of cardiovascular disease.

Nighttime exposure to artificial light appears to be associated with cardiac remodeling — and not in a good way, a team from Tulane University and Harvard recently found. Remodeling is typically a response to chronic stress and weakens the heart, potentially leading to heart failure, lead author, Lu Qi, explained.

People who were exposed to high levels of light had thickening of the wall of their left ventricles. Limiting nighttime exposure to light is a possible way to prevent heart disease.

The researchers wanted to know how cardiac remodeling changes the heart's structure and function. More than 11,000 participants in the UK Biobank who did not have cardiovascular disease were enrolled in the study. Each wore a light sensor on their wrist for a week to measure how much light they were exposed to overnight. Participants were given a cardiac electromagnetic imaging (MRI) scan three years later to examine the structure and function of their hearts.

Those who were exposed to light levels equivalent to that of a supermarket aisle had thickening of one of the chambers of the heart — the wall of the left ventricle — compared to participants exposed to low levels of light or no light.

This thickening reduced the space inside the left ventricle. The ability of the heart muscle to flex during a heartbeat also appeared to be reduced, an early indicator of functional decline of the muscle. Changes to the right ventricle and left atria, two other chambers of the heart, were also noted.

“Light pollution has emerged as a new risk factor for heart disease,” said Qi, a Distinguished Professor at the Tulane School of Public Health and Tropical Medicine. These findings, and those of other studies, suggest that limiting nighttime light exposure is a possible way to prevent heart disease.

Because it interferes with the quality and quantity of sleep, exposure to artificial light at night increases the risk of cardiovascular disease.

That means doctors caring for patients with atrial fibrillation or heart failure should discuss the sleep environment with those patients, according to a related editorial by Thomas Münzel and colleagues at University Medical Center in Mainz, Germany. They argue that providers should address the issue of light pollution and ask patients how dark their bedroom is, if they work night shifts and how much screen time they get after sunset.

Some simple, inexpensive ways to improve sleep and reduce nighttime exposure to artificial light include:

  • Use warm-colored bedside lighting. Look for lightbulbs that use a color temperature of 2,000-3,000 Kelvin.
  • Turn off all computer and smartphone screens 30 to 60 minutes before going to bed.
  • Install blackout curtains to block the light from streetlights.

Both the study and the editorial are published in the European Heart Journal.