The study, conducted by researchers from Massachusetts Hospital in Boston, United States, showed that turning on the lights during sleep contributes to brain stress and inflammation of the arteries, which may lead to a heart attack or stroke.
The researchers found that the higher the levels of exposure to artificial light at night, the higher the risk of heart disease later.
For every light level that increases by one standard deviation, the probability of having a heart attack increases by 35 percent over the next five years, and by 22 percent over the next ten years.
Ten years after the study, 17 percent of the participants had developed major cardiovascular problems.
It was also found that people who live in high-noise areas, near roads, or in poor neighborhoods were more susceptible to the negative effects of night light.
The study included 466,000 adults who did not have heart disease or cancer, and who underwent brain examinations at Massachusetts Hospital in Boston between 2005 and 2008.
The researchers relied on measuring the light level in the participants’ homes while they were sleeping using data from satellites.
The study was presented at the American Heart Association’s 2025 sessions, and has not yet been published in any peer-reviewed scientific journal.
Jonathan Cedernas, a sleep expert at Uppsala University in Sweden, said that the study confirms that sleeping in the dark is better for health, stressing that research on animals and humans has proven that night light disrupts neurophysiological systems and affects metabolism and inflammation.
The Headline website stated that this study proves that sleeping in complete darkness is the best option for obtaining a higher quality of sleep.
He advised covering the windows of the room before sleeping, blocking all openings, and wearing a sleep mask to create an ideal sleeping environment that helps the body relax.
