High risk of heart disease, high blood pressure and diabetes in later life is associated with children who spend too much time watching television, an Australian study showed Wednesday.
In what was declared world-first research, the University of Sydney found that six- to seven-year-olds who spent the most time watching television had narrower arteries in the back of their eyes.
This increased their chances of developing heart disease, high blood pressure and diabetes when they were older.
"Parents need to get their children up and moving and off the couch," said Dr Bamini Gopinath, the lead author.
The study examined 1,500 six- and seven-year-olds in 34 primary schools in Sydney.
On average, the children studied spent 1.9 hours a day watching television and 36 minutes a day in organised physical activity.
Those with the highest levels of physical activity -- just over an hour or more -- had significantly wider retinal arteries on average than those who spent less than half an hour a day being physically active.
"We found children with a high level of physical activity had a more beneficial microvascular profile compared to those with the lowest levels of physical activity," said Gopinath.
"This suggests unhealthy lifestyle factors may influence microcirculation early in life and increase the risk of heart disease and high blood pressure later in life."
Gopinath, senior research fellow at the Westmead Millennium Institute's Centre for Vision Research, added that excessive screen time leads to less physical activity, unhealthy dietary habits and weight gain.
"Replacing one hour a day of screen time with physical activity could be effective in buffering the effects of sedentary lifestyles on the retinal microvasculature in children," he said.
"Free play should be promoted and schools should have a mandatory two hours a week in physical activity for children."
The study is reported this week in Arteriosclerosis, Thrombosis and Vascular Biology: Journal of the American Heart Association.