Allowing your kids to watch TV or play on computers for more than two hours a day risks increasing their blood pressure.
A study of more than 5,000 children aged between two and 10 who spent this much time in front of a TV or computer screen were 30 per cent more likely to have high blood pressure than those who did not.
Scientists found that a lack of physical activity increased the risk even more – by 50 per cent.
The findings, published in the International Journal of Cardiology, are based on data from 5,221 children from eight European countries collected over two years.
Lead researcher Dr Augusto Cesar de Moraes, from the University of Sao Paulo, Brazil, said: "The study shows the number of new high blood pressure cases and the connection between physical activity and different sedentary behaviours with the risk of high blood pressure in European children.
"High blood pressure can cause cardiovascular problems later in life. For example, it increases the risk of ischemic heart disease."
Raised blood pressure in children is not defined by specific measurements, as it is in adults.
A child's blood pressure is said to be high if it is above that of 95 per cent of other children of the same age, height and gender.
The researchers concluded: "The figures are worrying, given that sedentary behaviours are common in infancy and subsequently, later in life."
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