The number of obese children will grow dramatically in the coming years and so will their death rates from heart disease, according to a pair of studies from the United States and Denmark published.

"If we don't take steps to reverse course, the children of each successive generation seem destined to be fatter and sicker than their parents," said David Ludwig of Children's Hospital Boston in a commentary in the New England Journal of Medicine, where the studies appear.

The Danish study, which tracked more than one quarter of a million school children in Copenhagen from 1930 to 1976, found that overweight children grew up to have more heart problems, particularly the boys.

The heavier they were as youngsters, particularly entering their teens, the greater the risk.

For example, a 13-year-old boy who was 25 pounds (11.2 kg) above the average weight was found to be 33 percent more likely than a child of normal weight to have a heart attack or some other problem caused by coronary heart disease (CHD) by age 60.

The finding "suggests that more children than ever before are facing increased risks of CHD in adulthood," said the team led by Jennifer Baker of the Center for Health and Society in Copenhagen.

About 17 percent of boys and 16 percent of girls now in the United States -- more than 9 million total -- are overweight.

The second study reported that out of this group, 25 percent of the boys now are obese, and that number is expected to increase to 30 to 37 percent by 2020, when they turn 35.

For females in that group, 32 percent of whom now are obese, the ratio will rise to 34 to 44 percent, according to that research team, led by Kirsten Bibbins-Domingo of the University of California, San Francisco.

That will lead to more heart disease, diabetes and high blood pressure at a younger age, and even aggressive treatment will not be able to stem the trend, they reported.

By 2035, the prevalence of heart disease will have increased by 5 to 16 percent, they estimated.

"Barring a major advance in the treatment of either excessive weight gain itself or its associated alterations in blood pressure, lipid levels and glucose metabolism, current adolescent overweight will have a substantial effect on public health far into the future," they concluded.

"My colleagues and I have predicted that pediatric obesity may shorten life expectancy in the United States by 2 to 5 years by mid-century -- an effect equal to that of all cancers combined," said Ludwig.

He also warned that "without effective intervention, the costs of obesity might well become catastrophic, arising not only from escalating medical expenses but also from diminished worker productivity caused by physical and psychological disabilities."