Changes to the retinal vessels give a good idea of what is going on in the rest of the body, particularly the heart," said Dr. Bamini Gopinath, a senior research fellow at the University of Sydney, who conducted the research. "In adults, we've found that narrower retinal arteries signal increased risk of hypertension [high blood pressure] and heart disease."
Gopinath and her colleagues evaluated 1,492six-year-olds in Sydney, tracking the hours they spent in both physical activity and sedentary pursuits.
The researchers took digital photos of the vasculature in the back of each child's eye and calculated the average vessel width.
Overall, the kids spent a daily average of 1.9 hours of screen time and 36 minutes of physical activity. But those kids who spent more than an hour in daily outside activity had wider vessels, on average, than those spending less than half an hour outside.
"We found that kids who spent more than one-and-a-half hours [in screen time] were more likely to have adverse effects on the retinal vessels," Gopinath said.
The narrowing associated with each hour of screen time was similar to the amount associated with a rise of 10 millimeters of mercury (mm Hg) in systolic blood pressure (the top number) in kids, the researchers found.
So, how much physical activity is enough?
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