U.S. researchers said that physically inactive children have a greater risk of heart problems, with symptoms emerging as early as adolescence.

Study leader Robert McMurray of the University of North Carolina reported on Dynamic Medicine that lack of physical activity can influence the metabolic syndrome in teenagers.

Metabolic syndrome including diabetes, high blood pressure, high cholesterol and obesity developed before adolescence.

The study followed the activity level of 389 children from ages seven to 10 in North Carolina public schools from 1990 through 1996. The researchers examined the children seven years later and found almost 5 percent had three or more characteristics of metabolic syndrome -- medical disorders such as glucose intolerance and high blood pressure. These disorders increase the risk of heart disease and diabetes.

Those with the metabolic syndrome were six times more likely to have low levels of physical activity as children. They had higher body mass index levels and cholesterol as well as lower levels of fitness and activity.

The researchers recommended that kids should be encouraged to keep fit or suffer the consequence later..

The study was published in the open access journal Dynamic Medicine.