Good sleep hygiene calls for, among other things, a cool, dark and relaxing environment. It turns out the dark part is key to helping prevent heart disease.
People who are exposed to more artificial sources of light at night have a greater risk of developing major heart conditions, according to research being presented this week at an American Heart Association conference. The study has implications for public health, because urban areas expose people to abundant amounts of artificial light at night, also called "light pollution," the researchers said.
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"We found a nearly linear relationship between nighttime light and heart disease: the more night-light exposure, the higher the risk," the study's senior author, Dr. Shady Abohashem, said in a news release. "Even modest increases in night-time light were linked with higher brain and artery stress."
Brain stress triggers immune response and blood vessel inflammation – a series of events that can cause arteries to harden over time. That, in turn, elevates the risk of heart attack and stroke, said Abohashem, who is also the head of cardiac PET/CT imaging at Massachusetts General Hospital.
For the study, researchers analyzed the health records of 466 people, all of whom had initial PET/CT scans between 2005 and 2008 at Massachusetts General Hospital. The scans were used to assess stress signals in the brain and inflammation in arteries.
To assess artificial light exposure, the researchers used information from 2016 New World Atlas of Artificial Night Sky Brightness, which uses satellite data to help measure light pollution. Researchers also incorporated data about artificial light exposure in people's homes.
Follow-up scans, conducted through 2018, showed that 17% of the people in the study had serious heart conditions.
Taking into account the participants' exposure to noise pollution, socioeconomic status and other factors, the association between nighttime artificial light exposure and heart disease remained.
To limit light pollution, cities could use motion sensors on lights and shield street lights. And, as is generally recommended for good sleep hygiene, people should limit screen use before bed and keep their sleeping areas dark at night, the researchers said.
The study's limitations included that it was observational in nature and relied on previously-collected data. This means that the researchers could establish a link between light pollution and heart conditions, but that they could not conclude that light pollution directly causes heart disease.
Also, the study participants all came from one health system and may not have been a nationally-representative group, the researchers said.