Artificial light at night may do more than disrupt sleep—a new study has suggested that it could also be linked to changes in the heart's structure and function, potentially increasing the risk of several cardiovascular diseases. Researchers from Tulane University found that greater exposure to light at night was associated with signs of adverse cardiac remodeling and reduced heart function. The findings were published in the European Heart Journal on September 9.
Cardiovascular diseases are the leading cause of death globally—one person dies every 34 seconds from cardiovascular disease in the U.S., highlighting the importance of improving understanding about possible prevention. The team analyzed data from more than 11,000 participants in the UK Biobank who were given devices to wear on their wrists to monitor their exposure to nighttime light over a seven-day period. Participants then underwent cardiovascular magnetic resonance (CMR) imaging, allowing researchers to assess the structure and performance of their hearts.
The researchers found that those exposed to higher levels of nighttime light had increased heart muscle mass and thicker heart walls—changes that can precede cardiovascular disease. They also had signs of impaired heart function affecting both the left and right sides of the heart. Dr Lu Qi, study lead and director of the Tulane University Obesity Research Center, told Newsweek they found "nighttime light exposure may impact the heart partly through shortening sleep duration and quality." This is likely because nighttime light is believed to disrupt the body's circadian rhythm—the body’s natural 24-hour clock that affects a wide range of systems.
"The findings, together with those from other studies, suggest bedroom light matters regarding cardiovascular health. Turning off light when sleeping may benefit the heart," Qi said. Light pollution refers to excessive or unwanted artificial light in the environment.
Common sources include streetlights, illuminated buildings, vehicle headlights, electronic devices and outdoor advertising. Previous studies have associated nighttime light exposure with obesity, hypertension, diabetes and increased cardiovascular disease risk, which some research has attributed to impaired cardiac autonomic regulation, elevated systemic inflammation and disruption to circadian rhythm. Explaining why this could be the case, Martin Young, a professor of medicine at the University of Alabama at Birmingham, who was not involved in the study, told Newsweek that "every cell in our body possesses a molecular circadian clock, that orchestrates biological processes, ensuring that these processes occur at the correct time of day." He added that circadian clocks are "very sensitive to the environment, particularly light," meaning "light exposure at the ‘wrong’ time, such as at night, can disrupt molecular clocks," and this "results in a loss of temporal synchronization between the different cells and organs within the body." Young said that lab-based studies have indicated that disruption of the circadian clock within heart cells prevents them from removing "damaged cellular components while we sleep," and replacing them "with fully functional components before waking," meaning that sleep deprivation or circadian disruption "appears to prevent these normal cycles from occurring, leading to accumulation of damaged cellular components and pathologic growth of the heart." Cardiovascular disease is an umbrella term covering conditions that affect the heart and blood vessels, meaning that symptoms can vary depending on the specific condition.
"The importance of this study cannot be overstated," Young said. He added that researchers have known for some time that "environmental factors and behaviors that reduce sleep or impair our natural circadian rhythms increase risk for various cardiometabolic diseases, including obesity, diabetes, hypertension, stroke, and heart attacks," and that the findings highlight an "urgent need to improve our understanding of how factors such as exposure to light at night increases our risk for disease development." He said, given the findings, it would be advisable to reduce light exposure at night, and said that "when this might not be possible, then blocking the blue light wavelength that impairs sleep and circadian rhythms, would be one alternative." He also said finding ways to "'resynchronize’ clocks" is another option. "Exposure to light, eating a decent breakfast, and being physically active in the morning will help to reset and align clocks within the body," he said.
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