Too much screen time may be hurting kids’ hearts: Study

Research Highlights

♦ More time using electronic devices or watching TV among children and young adults was linked with higher cardiometabolic disease risk, including high blood pressure, high cholesterol and insulin resistance, based on data from more than 1,000 participants in Denmark.

♦ The association between screen time and cardiometabolic risks was strongest in youth who slept fewer hours, suggesting that screen use may harm health by "stealing" time from sleep, researchers said.

♦ Researchers said the findings underscore the importance of addressing screen habits among young people as a potential way to protect long-term heart and metabolic health.

Screen time tied to early heart and metabolic risks

Children and teens who spend many hours on TVs, phones, tablets, computers or gaming systems appear to face higher chances of cardiometabolic problems, such as elevated blood pressure, unfavorable cholesterol levels and insulin resistance. The findings are reported in the Journal of the American Heart Association, an open-access, peer-reviewed journal of the American Heart Association.

A 2023 scientific statement from the American Heart Association reported that "cardiometabolic risk is accruing at younger and younger ages," and that only 29% of U.S. youth ages 2 to 19 had favorable cardiometabolic health in 2013-2018 National Health and Nutrition Examination Survey data.

Danish cohorts show a consistent pattern

An evaluation of more than 1,000 participants from two Danish studies found a clear connection: more recreational screen time was significantly associated with greater cardiovascular and overall cardiometabolic risk among children and adolescents.

"Limiting discretionary screen time in childhood and adolescence may protect long-term heart and metabolic health," said study lead author David Horner, M.D., PhD., a researcher at the Copenhagen Prospective Studies on Asthma in Childhood (COPSAC) at the University of Copenhagen in Denmark. "Our study provides evidence that this connection starts early and highlights the importance of having balanced daily routines."

What researchers measured

The team analyzed two COPSAC groups: one of 10-year-olds followed in 2010 and one of 18-year-olds followed in 2000. They examined how leisure screen use related to cardiometabolic risk factors. Screen time included watching TV and movies, gaming and time on phones, tablets or computers for fun.

To capture overall risk, researchers created a composite cardiometabolic score based on multiple components of metabolic syndrome, including waist size, blood pressure, high-density lipoprotein or HDL "good" cholesterol, triglycerides and blood sugar levels. They adjusted for sex and age. The score reflects each participant's risk relative to the study average (in standard deviations): 0 indicates average risk, and 1 indicates one standard deviation above average.

Each hour adds up

The analysis showed that every additional hour of recreational screen time was linked with an increase of about 0.08 standard deviations in the cardiometabolic score for the 10-year-olds and 0.13 standard deviations for the 18-year-olds. "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 said.

"It's a small change per hour, but when screen time accumulates to three, five or even six hours a day, as we saw in many adolescents, that adds up," he said. "Multiply that across a whole population of children, and you're looking at a meaningful shift in early cardiometabolic risk that could carry into adulthood."

Sleep appears to intensify the risk

Short sleep and later bedtimes strengthened the relationship between screen time and cardiometabolic risk. Youth who slept less showed notably higher risk linked to the same amount of screen exposure.

"In childhood, sleep duration not only moderated this relationship but also partially explained it: about 12% of the association between screen time and cardiometabolic risk was mediated through shorter sleep duration," Horner said. "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."

Metabolic "fingerprint" linked to screen use

In a machine learning analysis, investigators identified a distinctive pattern of blood metabolites that appeared to correlate 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," he said. "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.

"Recognizing and discussing screen habits during pediatric appointments could become part of broader lifestyle counseling, much like diet or physical activity," he said. "These results also open the door to using metabolomic signatures as early objective markers of lifestyle risk."

Practical guidance from experts

Amanda Marma Perak, M.D., M.S.CI., FAHA, chair of the American Heart Association's Young Hearts Cardiovascular Disease Prevention Committee, who was not involved in this research, said focusing on sleep is a great starting point to change screen time patterns.

"If cutting back on screen time feels difficult, start by moving screentime earlier and focusing on getting into bed earlier and for longer," said Perak, an assistant professor of pediatrics and preventive medicine at Northwestern University Feinberg School of Medicine in Chicago.

Adults can also set an example, she said. "All of us use screens, so it's important to guide kids, teens and young adults to healthy screen use in a way that grows with them. As a parent, you can model healthy screen use -- when to put it away, how to use it, how to avoid multitasking. And as kids get a little older, be more explicit, narrating why you put away your devices during dinner or other times together.

"Make sure they know how to entertain and soothe themselves without a screen and can handle being bored! Boredom breeds brilliance and creativity, so don't be bothered when your kids complain they're bored. Loneliness and discomfort will happen throughout life, so those are opportunities to support and mentor your kids in healthy ways to respond that don't involve scrolling."

Important caveats and next questions

Because this work is observational, it reveals associations rather than direct cause and effect. In addition, screen use for the 10-year-olds and 18-year-olds was reported by parents through questionnaires, which may not perfectly reflect actual time spent on screens.

Horner noted that future studies could test whether reducing screen exposure in the hours before bedtime, when screen light may disrupt circadian rhythms and delay sleep onset, helps lower cardiometabolic risk.

Study details, background and design

♦ The two prospective research groups at COPSAC in Denmark consisted of mother-child pairs, with analysis of data collected at planned clinical visits and study assessments from the birth of the children through age 10 in the 2010 study group and age 18 in the 2000 study group.

♦ Through questionnaires, parents of children in the 10-year-old group and 18-year-olds detailed the number of hours the young participants spent watching TV or movies, gaming on a console/TV and using phones, tablets or computers for leisure.

♦ For the 2010 group, the number of hours of screen time was available for 657 children at age 6 and 630 children at age 10. Average screen time was two hours per day at age 6, and 3.2 hours per day at age 10, representing a significant increase over time.

♦ For the 2000 group of 18-year-olds, screen time was available for 364 individuals. Screen time at 18 years was significantly higher at an average of 6.1 hours per day.

♦ Sleep was measured by sensors over a 14-day period.

Reference: David Horner, Marie Jahn, Klaus Bønnelykke, Bo Chawes, Trine Flensborg‐Madsen, Ann‐Marie Malby Schoos, Jakob Stokholm, Morten Arendt Rasmussen. Screen Time Is Associated With Cardiometabolic and Cardiovascular Disease Risk in Childhood and Adolescence. Journal of the American Heart Association, 2025; 14 (16) DOI: 10.1161/JAHA.125.041486