COPENHAGEN, Denmark – Children and teenagers who spend long hours glued to phones, tablets, and televisions could face higher risks of developing heart and metabolic problems later in life — particularly if they also get too little sleep, a new study has found.
The research, published in the Journal of the American Heart Association, linked every extra hour of recreational screen time to measurable increases in cardiometabolic risk among young people.
Scientists from the University of Copenhagen’s Copenhagen Prospective Studies on Asthma in Childhood (COPSAC) analysed data from more than 1,000 participants aged 10 and 18, tracking their screen habits, sleep duration, and early indicators of heart and metabolic health.
“A child spending three extra hours a day in front of a screen could have roughly a quarter to half a standard deviation higher risk than their peers,” said lead author David Horner, a researcher at COPSAC.
“It might seem small per hour, but over time, and across a population, it adds up to a significant shift in early health risks that can follow into adulthood.”
The researchers developed a composite cardiometabolic score based on waist circumference, blood pressure, cholesterol, triglycerides, and blood sugar levels.
They found that the link between screen exposure and health risk grew stronger with age, with 18-year-olds showing greater increases than 10-year-olds.
Biological “Fingerprint” of Screen Time
Using machine learning, the team identified a distinctive blood metabolite pattern — described as a “screen-time fingerprint” — suggesting that prolonged exposure to screens may trigger early biological changes.
They also found that sleep duration explained about 12 per cent of the relationship between screen time and metabolic risk, meaning insufficient sleep partly mediates how screen use harms the body.
“In childhood, shorter sleep seems to amplify the impact of screen use on metabolic changes,” Horner said.
Adolescents were found to spend an average of five to six hours daily on recreational screen time — a habit the study warns could silently shape their long-term heart health.
Experts Urge Family Action
Dr. Amanda Perak, who chairs the American Heart Association’s Young Hearts Cardiovascular Disease Prevention Committee, said families should approach screen reduction gradually.
“If reducing screen time feels overwhelming, begin by moving it earlier in the day and focusing on getting into bed earlier and for longer,” she said.
She urged parents to lead by example: “All of us use screens, so it’s important to model healthy, mindful usage. Put devices away during meals, explain why, and encourage screen-free family time.”
Researchers also noted that boys showed stronger associations between screen time and cardiometabolic risks, although the difference was not statistically significant.
Early Intervention Matters
The findings underscore that cardiometabolic risks can begin accumulating early in life — influenced by lifestyle factors such as screen use, sleep patterns, diet, and physical activity.
While the study is observational and cannot prove direct causation, it strengthens evidence that screen time should be treated as an independent behavioural risk factor for heart and metabolic disorders.
“Limiting discretionary screen time in childhood and adolescence may protect long-term heart and metabolic health,” Horner concluded.