Exposure to light during nighttime sleep could lead to potentially harmful changes in the structure and function of the heart, according to a study published Wednesday in the European Heart Journal.
Previous research has shown a link between sleeping at night with light exposure and an increased risk of coronary artery disease, heart attack, heart failure and stroke. The new study is the first to look at how this also affects the structure and function of the heart.
Changes in the heart – known as remodeling – may help explain the increased risk of heart problems associated with too much light at night, said lead researcher Dr. Lu Qi, of the Celia Scott Weatherhead School of Public Health and Tropical Medicine at Tulane University.
“The conclusion is clear: darkness deserves to be recognized as a vital sign, as essential for cardiovascular health as blood pressure control and clean air,” Dr. Thomas Münzel, an environmental cardiologist at the University Medical Center of Johannes Gutenberg University in Mainz, Germany, and colleagues wrote in an editorial accompanying the study.
(A study denies that the body has a protein absorption limit per meal)
The researchers analyzed data from 11,071 participants enrolled in the UK Biobank, a huge database that began recruiting participants in 2005 and collects information on demographics, health and lifestyle. The people who participated in the study They wore a light and motion sensor on their wrist for seven days and, a few years later, they underwent an MRI of the heart. At the beginning of the study, none of them suffered from cardiovascular disease.
The researchers compared people who were exposed to almost no light at night while sleeping with others who were exposed to at least 3 lux – a lux is a unit of measurement for illumination – which would still correspond to a very dark room, explained Kristen Knutson, an associate professor of Sleep Medicine at Northwestern University Feinberg School of Medicine, who was not related to the study.
However, closed eyes would be able to detect light, he added.
Street light filtering through blinds, clock radio lighting, and LED lights from equipment such as air purifiers or room humidifiers were possible sources of nighttime light in the study, Qi said.
(Do single men smell stronger? A psychologist analyzes what a study reveals)
After adjusting the results to take into account demographic, lifestyle, health and environmental factors, the researchers found that any increase in light exposure above 3 lux during nighttime sleep could be associated with subtle but measurable heart damage.
For example, participants in the highest light exposure group had, on average, a 2.4 percent larger left ventricle (a chamber of the heart), a 1.5 percent thicker heart wall, and a 1.9 percent reduction in the heart’s ability to contract, compared to participants who slept in the darkest rooms.
(An expert explains when fatigue is no longer normal and the signs that women should pay attention to)
Each of those changes in the heart looks smallbut it has been linked to cardiovascular disease and stroke.
“If we look at the various functional and structural results together, they are quite considerable,” Qi said.
