Kids watching TV for hours? Beware of health risks

The study, which looked at 1,500 six-to-seven-year-old children in 34 primary schools, showed that the increased health risks from each hour a day of TV was similar to that associated with an increase in blood pressure, University of Sydney researchers said.

Physically active children had significantly wider average retinal arteries than their largely sedentary counterparts, reports the journal Arteriosclerosis, Thrombosis and Vascular Biology: Journal of the American Heart Association.

"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 Bamini Gopinath, who led the study at the University of Sydney Centre for Vision Research.

"Excessive screen time leads to less physical activity, unhealthy dietary habits and weight gain," Gopinath said, according to a Vision Research statement.

"Free play should be promoted and schools should have a mandatory two hours a week in physical activity for children," he added.

Physical activity enhances blood flow and has a positive effect on the linings of blood vessels. On average, the children spent 1.9 hours per day in screen time and 36 minutes a day in organised physical activity.