Children as young as six are experiencing early artery damage caused by watching too much television and not getting enough exercise, according to research.
Scientists found that youngsters who spent the majority of their free time watching television had narrowed blood vessels in their eyes, which is a known warning sign of heart disease.
During the study researchers measured differences in the size of the micro-arteries at the back of the eye.
Six and seven-year-olds who lived a sedentary lifestyle had an average retinal arteriolar narrowing of 2.3 microns - a micron is one thousandth of a millimetre.
Meanwhile, those who regularly complete outdoor physical activity had retinal blood vessels that were 2.2 microns wider than those who did the least exercise.
The narrowing associated with each extra hour of TV or computer viewing was similar to that which accompanies a blood pressure increase in children of 10 millimetres of mercury (mmHG).
Lead researcher, Dr Bamini Gopinath, from the Centre for Vision Research at the University of Sydney, Australia, said: "We found that children with a high level of physical activity had a more beneficial microvascular profile compared to those with the lowest levels of physical activity.
"This suggests that unhealthy lifestyle factors may influence microcirculation early in life and increase the risk of cardiovascular disease and hypertension (high blood pressure) later in life."