A new study finds that children who are inactive may be six times more prone to develop heart disease as teenagers when compared to their active counterparts.
Moreover, the cluster of symptoms pointing to heart trouble, known as the metabolic syndrome, can show up as early at the teen years, the study said.
A team of researchers at the University of North Carolina, led by Robert McMurray, measured key health indicators in nearly 400 kids between seven and 10, including height, body mass, percentage of body fat, blood pressure and cholesterol levels.
Frequency and duration of physical exercise was also monitored.
Seven years later, the same children were reexamined as teenagers to see how many had developed the tell-tale signs of metabolic syndrome.
Nearly five percent of the adolescents had three or more of the condition's core symptoms, concluded the study, published in the British journal Dynamic Medicine.
This was consistent with previous research showing that four to nine percent of adolescents in the United States have some combination of glucose intolerance, hypertension, obesity and a worrying cholesterol count.
But until now no one has tracked the same group of children over time to study the link between physical activity in early childhood and the chances of developing signs of heart disease.
McMurray found that the adolescents with the syndrome were six times likelier to have had low aerobic fitness as children, and five times likelier to have low levels of physical activity when the study began.
At best, these kids spent less than 20 minutes a day walking briskly, riding a bike at a moderate pace or performing some equivalent activity.
The US Centers for Disease Control and Prevention (CDC), based in Atlanta, recommends that children exert themselves at this level for at least one hour per day.
"This shows efforts need to begin early in childhood to increase exercise," said McMurray. "Children today live a very sedentary life and are prone to obesity."
"It's obvious now that there is a link and this is something which we need to pay attention to by encouraging our kids to keep fit or suffer the consequences later in life."