In a world first study researchers have found six-year-olds who spent the most time watching television had narrower arteries in the back of their eyes, increasing their chances of heart disease, high blood pressure and diabetes in later life.
The study, reported this week in "Arteriosclerosis, Thrombosis and Vascular Biology: Journal of the American Heart Association", showed the increased health risks from each hour a day of television was similar to that associated with an increase of 10 mm HG in systolic blood pressure, researchers said.
The study looked at one and a half thousand 6-to-7-year-old children in 34 primary schools in Sydney. Those who regularly participated in outdoor physical activity had wider average retinal arterioles (arteries behind the eyes) compared to children with the lowest activity levels.
"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 Dr Bamini Gopinath, lead author and senior research fellow at the University of Sydney's Centre for Vision Research.
"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."
Physical activity enhances blood flow and has a positive effect on the linings of blood vessels. Retinal microvascular diameter is a marker for cardiovascular disease and high blood pressure in adults, but this is the first study to show a sedentary lifestyle in childhood is linked to a narrowing of the vessels in the retina.
On average, the children spent 1.9 hours per day in screen time and 36 minutes a day in organised physical activity. Children with the highest levels of physical activity, just over an hour or more, had significantly wider average retinal arteries than those who spent less than half an hour a day being physically active.
"Excessive screen time leads to less physical activity, unhealthy dietary habits and weight gain," Dr Gopinath said. "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.
"Free play should be promoted and schools should have a mandatory two hours a week in physical activity for children. Parents need to get their children up and moving and off the couch," Dr Gopinath said. "Parents can also lead the way by being more physically active themselves."
Co-authors are: Louise A. Baur, Ph.D.; Jie Jin Wang, Ph.D.; Louise Hardy, Ph.D.; Erdahl Teber, Ph.D.; Annette Kifley, M.B.B.S.; Tien Y. Wong, M.D., Ph.D.; and Paul Mitchell, M.D., Ph.D. Author disclosures are on the manuscript.
The Australian National Health and Medical Research Council, the Westmead Millennium Institute and the Vision Co-operative Research Centre funded the research.