How too much screen time affects kids’ heart health and what can reduce the risk

By Hugo Francisco de SouzaReviewed by Susha Cheriyedath, M.Sc.Aug 7 2025

Researchers in Denmark show that every extra hour of daily screen use in kids and teens increases cardiometabolic risk, but getting enough sleep may help protect their hearts.

Study: Screen Time Is Associated With Cardiometabolic and Cardiovascular Disease Risk in Childhood and Adolescence. Image Credit: vinnstock / Shutterstock

In a recent study published in the Journal of the American Heart Association, researchers leveraged data from two Danish longitudinal cohorts comprising more than 1,000 mother-child participants to uncover the impacts of screen time on concurrent cardiometabolic health among children and adolescents. The study revealed that increased screen time, an increasingly worrisome trend in today's society, is associated with higher cardiometabolic risk.

Encouragingly, however, longer sleep duration might help to weaken this association, with adequate sleep linked to a reduced strength of the relationship between screen time and adverse cardiometabolic outcomes. Researchers also identified a novel blood-based "metabolomic signature" for high screen time that predicted screen time exposure across cohorts, and separately found that higher screen time in adolescents was associated with a higher predicted risk of future cardiovascular disease based on an NMR-derived CVD risk score.

These findings underscore the critical interplay between screen use and sleep in shaping early-life cardiovascular health, while emphasising that the results are observational and cannot prove causality, thereby shaping future public health policy.

Background

Cardiovascular diseases (CVDs) remain the world's leading non-communicable causes of human mortality, with their origins traceable to exposures from childhood and even infancy. The accumulation of cardiometabolic risk (CMR) factors, such as high blood pressure, adverse cholesterol levels, excess waist circumference, and insulin resistance during youth, sets the stage for adult disease.

Alarming, our increasingly sedentary world of today, dominated by screen time, exacerbates known CVD-associated risk factors, including obesity and unhealthy dietary patterns. While previous research has linked high screen time to these individual risk factors, the relationship is complex, and it is often difficult to untangle the effects of screen time from other lifestyle factors like physical activity and, most importantly, sleep.

CVDs' staggeringly high mortality rates (~19.8 million / 32% of all global deaths) and the fact that their global burden is rising necessitate the identification of early-life interventions that may safeguard our future generations from the dangers of heart disease.

About the study

The present study aims to address this gap in the literature by leveraging two deeply phenotyped longitudinal Danish cohorts (Copenhagen Prospective Studies on Asthma in Childhood [COPSAC2010 and COPSAC2000]) to provide a more comprehensive picture of how screen time, sleep, and cardiometabolic health are intertwined during critical early developmental periods.

The study dataset comprised socio-demographic and medical health records from more than 1,000 children (6-10 years) and adolescent (~18 years) participants. Screen usage (including screen time) was collected via discretionary reporting (parents) or from adolescents. The study's primary outcome of interest was a composite cardiometabolic risk (CMR) score, calculated from Z-scores of five key measures: 1. waist circumference, 2. systolic blood pressure, 3. high-density lipoprotein (HDL) cholesterol, 4. triglycerides, and 5. glucose.

Lifestyle factors, including sleep duration and physical activity, were objectively measured using accelerometers (Actigraph GT3X+) worn for 14 days. To explore the underlying biology of screen time-sleep-CVD risk associations, nuclear magnetic resonance (NMR) metabolomics of participants' blood samples was carried out, and a supervised machine learning model was trained to identify a "metabolic signature" of high screen time.

Linear mixed models assessed the association between screen time and CMR. In tandem with metabolic signature profiles, these were used to generate a 10-year CVD risk score for each participant.

Study findings

The present study identified a distinct positive link between screen time (among children and adolescents) and concurrent cardiometabolic risk. Even after accounting for socio-demographic and medical confounders (age, sex, chronic disease), each additional hour of daily screen time was associated with a significant increase in the CMR score in both children (β=0.08, P=0.021) and adolescents (β=0.13, P=0.001).

Crucially, sleep duration was a powerful moderator of this risk. The association between screen time and higher CMR was significantly stronger in children and adolescents who slept less (P for interaction = 0.029 in children, 0.012 in adolescents).

In childhood, sleep duration also mediated about 12% of the association between screen time and CMR, and later sleep onset was linked to a higher risk. In adolescence, later sleep onset was independently associated with CMR, and sleep duration again moderated the relationship. This indicates that adequate sleep may help buffer against the metabolic effects of high screen time.

The metabolomics analysis identified a distinct "signature" comprising 37 individual biomarkers associated with screen time and predictive of screen time exposure. This signature, which included elevated triglycerides and altered lipoprotein profiles, was robust enough to be identified in the childhood cohort and then successfully validated in the adolescent cohort. Separately, adolescents were observed to be more vulnerable to the effects of higher screen time, which was significantly associated with a higher predicted 10-year risk of cardiovascular disease (β=0.07, P=0.017) based on an adult-trained NMR cardiovascular risk score.

In addition, no significant associations between screen time and anthropometric measures were found in children, while in adolescents, particularly boys, screen time was linked to higher BMI, fat mass, and other body composition measures.

Although some associations appeared stronger in boys, formal interaction tests showed no statistically significant sex differences.

Conclusions

The present study provides strong evidence linking increased screen time and poor cardiometabolic health in both childhood and adolescence, but as an observational study, it cannot prove causation. It demonstrates a dose-response association between these factors. Notably, sleep duration was found to potentially protect against the detrimental impacts of higher screen time. Finally, identifying a blood-based metabolomic signature for high screen time and a separate CVD risk score associated with screen time in adolescents offers mechanistic insights and opens the door for new biomarkers to identify at-risk youth and implement timely interventions.

The authors highlight that their moderation and mediation analyses are exploratory and that reported screen time data could be subject to bias. They recommend that future research use objective measures of screen exposure, sleep timing, and duration, and explore whether interventions targeting both screen use and sleep patterns can improve cardiometabolic outcomes.