The authors of a study published in the Journal of the American Heart Association said the link between screen time and cardiometabolic risk — including high blood pressure, high cholesterol and insulin resistance — was even stronger in children and teens with poor sleep habits.

The more time children spend on screens, the higher their risk factors for cardiometabolic disease, including high blood pressure, high cholesterol and insulin resistance, according to a study published this month in the Journal of the American Heart Association.

The authors found that each extra hour of screen time — including watching movies or TV, gaming, and using cellphones, tablets or computers for leisure — increased youths’ overall cardiometabolic risk compared to the average for children their age.

“This was true even after accounting for diet, exercise and sleep,” David Horner, M.D., Ph.D., the study’s lead author, told The Defender.

The link between screen time and cardiometabolic risk was even stronger in youths with poor sleep habits.

“Poor sleep, shorter nights and later bedtimes” all amplified the risk, Horner said.

The analysis suggests screen use may reduce sleep duration or extend the time it takes for a person to fall asleep, possibly through blue light exposure or increased stress, Horner said.

“These findings don’t surprise me at all,” Dr. Holly Groh, a retired Louisiana ophthalmologist who has tracked research on screen time’s negative health impacts for years, told The Defender.

“Taking a child’s world and making it into a few small inches of stimulation” from an electronic screen has “far-reaching effects,” she said.

According to Groh, screen time affects not only a child’s heart and sleep, but their eyes, brain, mental health and hormonal system.

Screen time created a ‘metabolic signature’ in the blood

Screen habits leave measurable biological traces in the blood “before any disease is visible,” Horner said.

Using machine learning, the researchers found they could accurately predict which children had higher screen times by looking for certain biomarkers in their blood.

These biomarkers were a “metabolic signature” related to screen time, according to the authors’ report. It said:

“The identified metabolic signature included 37 biomarkers, many of which have previously been linked to obesity‐related traits and lipid metabolism, such as elevated triglycerides in various very low‐density lipoprotein subclasses and reduced large HDL cholesterol fractions.”

The study’s findings suggest that limiting recreational screen time in childhood and adolescence may “protect long-term heart and metabolic health,” Horner said in a press release.

“Recognizing and discussing screen habits during pediatric appointments could become part of broader lifestyle counseling, much like diet or physical activity,” he said.

Horner recommended that children avoid watching screens within two hours of bedtime, balance screen use with physical exercise, and build routines that include lots of offline activities.

How the research was conducted

The researchers examined data from over 1,000 Danish youths in two previous Danish cohort studies. One study gathered health data from 700 children from birth to age 10. The other gathered health data from roughly 400 children from birth to age 18.

Parents documented how many hours their child spent on recreational screen time on weekdays and weekends. The 18-year-olds reported their own hours.

At age 6, the average screen time was two hours a day. At ages 10 and 18, the averages were 3 and 6 hours, respectively.

The researchers also measured cardiometabolic risk factors, including waist circumference, blood pressure, cholesterol and blood sugar levels, which they adjusted for age and sex. These factors influence a person’s risk of having a heart attack and stroke, according to Harvard Medical School.

The authors compiled the data to create a composite cardiometabolic risk score for each child or teen that reflected the youth’s overall risk compared to the average for children their age.

For 10-year-olds, the score rose by about 0.08 standard deviations. For 18-year-olds, it went up by 0.13 standard deviations.

A standard deviation is a measure of how dispersed data is in relation to an average, according to the National Institutes of Health’s National Library of Medicine.

The change may look small, “but when screen time accumulates to three, five or even six hours a day, as we saw in many adolescents, that adds up,” Horner 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.”

It’s not just sitting around that makes time on screens harmful

Prior studies on the health impacts of screen time have attributed poor health outcomes to the sedentary nature of watching screens.

However, authors of the Danish study said sedentariness didn’t explain the symptoms they identified in their study. Their statistical model accounted for lifestyle factors, including the amount of time a child was sedentary and the child’s diet.

Screen time itself appeared to increase kids’ risk via “independent mechanisms,” such as “poor stress regulation and high sympathetic arousal,” they said.

What about wireless radiation?

The study report did not mention that most screens emit wireless radiation.

Dr. Robert Brown, vice president of Scientific Research and Clinical Affairs for the Environmental Health Trust, said, “We need to understand that unless a device is hardwired, the screen is irradiating its observer with radiofrequency radiation.”

This radiation causes oxidative stress in the body’s cells, “causing negative systemic health effects — both in our children and in adults,” he said.

The study authors said the research was observational, meaning it didn’t prove that screen time increased the risks. They also noted their results could be biased because parents and 18-year-olds may not have accurately reported their screen time use.

The authors called for future studies to confirm their findings.

Horner is a researcher at the Copenhagen Prospective Studies on Asthma in Childhood at the University of Copenhagen in Denmark.

Numerous entities funded the study, including the Lundbeck Foundation, Denmark’s Ministry of Health, the Danish Council for Strategic Research, the Capital Region Research Foundation and the European Research Council.

This article was originally published by The Defender — Children’s Health Defense’s News & Views Website under Creative Commons license CC BY-NC-ND 4.0. Please consider subscribing to The Defender or donating to Children’s Health Defense.