A Canadian study published in the International Journal of Behavioral Nutrition and Physical Activity (IJBNPA) found that every extra weekly hour watched could add half a millimetre to their waist circumference and reduce muscle fitness.
Experts say children should not watch more than two hours of TV a day and researchers found that the average amount of television watched by the youngest children at the start of the study was 8.8 hours a week.
However this increased on average by six hours over the next two years to reach 14.8 hours a week by the age of four-and-a-half and fifteen per cent of the children in the study were watching more than 18 hours per week by that age, according to their parents.
The study said the effect of 18 hours of television at 4.5 years of age would, by the age of 10, result in a waistline increase of 7.6mm.
As well as measuring waist circumference, the researchers also carried out a standing long jump test to measure each child’s muscular fitness and athletic ability.
An extra weekly hour of TV can decrease the distance a child is able to jump from standing by 0.36cm, the study said.
The researchers said that further research was needed to work out whether television watching is directly responsible for the health issues they observed.
Source: International Journal of Behavioral Nutrition and Physical Activity