Spending an excessive amount of time on smartphones and other electronic devices could put children and young adults’ heart health in jeopardy, potentially leaving them susceptible to dangerous health conditions that raise the risk of heart disease.
The connection is especially strong in those who get less sleep, Danish researchers said Wednesday, suggesting that screen time could be “stealing” sleep time. Getting more sleep helps to lower the risk of the conditions they flagged, which include high blood pressure, high cholesterol, and insulin resistance.
“In childhood, sleep duration not only moderated this relationship but also partially explained it: about 12 percent of the association between screen time and cardiometabolic risk was mediated through shorter sleep duration,” Dr. David Horner, a researcher at the University of Copenhagen, said in a statement. “These findings suggest that insufficient sleep may not only magnify the impact of screen time but could be a key pathway linking screen habits to early metabolic changes.”
Both sleep duration and timing were major factors, according to Horner and his team. A shorter amount of time spent asleep and getting to sleep later was linked to a significantly higher risk associated with the same amount of screen time as others who slept for more hours and went to sleep earlier, the researchers said.
To reach these conclusions, they analyzed data from more than 1,000 kids and teenagers in Denmark. They used data from 10-year-olds taken in 2010 and data from 18-year-olds recorded in 2000. The data includes how much time they spent watching TV or movies, gaming, or using phones, tablets and computers. The researchers noted that parents reported their children’s screen time in questionnaires.
To assess the impacts of their screen use, Horner and his team developed a scoring system that would reflect overall risk, taking into account their waist size, blood pressure, age, and other biological factors. An “average” risk was set at zero, and one was a point above the average.
Calculating this score for the included participants, they found that each extra hour of screen time worsened that risk for both age groups.
“This means a child with three extra hours of screen time a day would have roughly a quarter to half a standard-deviation higher risk than their peers,” Horner explained.
Screen time added up to as many as six hours a day, he noted.
The research also included an analysis done using machine learning, which identified a signature in the participants’ blood that appeared to be associated with screen time.
“We were able to detect a set of blood-metabolite changes, a ‘screen-time fingerprint,’ validating the potential biological impact of the screen time behavior,” said Horner. “Using the same metabolomics data, we also assessed whether screen time was linked to predicted cardiovascular risk in adulthood, finding a positive trend in childhood and a significant association in adolescence. This suggests that screen-related metabolic changes may carry early signals of long-term heart health risk.”
In the U.S., this problem may be widespread, with cardiometabolic risk seen “at younger and younger ages,” according to a 2023 scientific statement from the American Heart Association.
Only 29 percent of American youth between the ages of two and 29 years old had good cardiometabolic health based on data collected between 2013 and 2018, the statement said.
On average, U.S. children between the ages of eight and 18 spend 7.5 hours each day on screens, according to the American Academy of Child and Adolescent Psychiatry.
To address these possibly global effects, the researchers hope to examine whether limiting screen use in the hours before sleep could help to reduce cardiometabolic risk.
Until then, experts advise transitioning away from screens in stages.
“If cutting back on screen time feels difficult, start by moving screentime earlier and focusing on getting into bed earlier and for longer,” Dr. Amanda Perak, an assistant professor of pediatrics and preventive medicine at Northwestern University Feinberg School of Medicine, said.
Perak, the chair of the American Heart Association’s Young Hearts Cardiovascular Disease Prevention Committee, was not involved in the research.
The study was published in the Journal of the American Heart Association.