WASHINGTON - Being overweight as a child significantly increases the risk for heart disease in adulthood as early as age 25, researchers report today in a large new study, providing the strongest evidence yet that the obesity epidemic is spawning a generation prone to serious health problems later in life.

The study of nearly 277,000 Danish children found those who were overweight at ages 7 to 13 were far more likely to develop heart disease between 25 and 71 - even those who were just a little chubby as kids, and possibly regardless of whether they lost the weight when they grew up.

"This is incredibly important," said Jennifer Baker of the Institute of Preventive Medicine in Copenhagen, who led the research, published in the New England Journal of Medicine. "This is the first study to convincingly show that excess childhood weight is associated with heart disease in adulthood, or with any significant health problem in adulthood."

Accompanying the Danish study was an analysis of U.S. health statistics that projects teenage obesity will increase the nation's heart disease rate by at least 16 percent by the year 2035, causing more than 100,000 additional cases.

David Ludwig of Harvard Medical School, who wrote an accompanying editorial, described the two studies as "a frightening glimpse" of the future, and added: "Childhood obesity is not a cosmetic problem. It can have profound long-term consequences for adult illness and death."

The proportion of U.S. children who are overweight has tripled since 1976. It has caused a jump in children with Type 2 diabetes, previously known as adult-onset diabetes. And children are increasingly being diagnosed with high blood pressure.

Baker and her colleagues analyzed height and weight data for schoolchildren between 1955 and 1960 and scoured hospital records between 1977 and 2001 to see who was later hospitalized for heart problems.

Risk increased with any amount of excess weight in childhood. "Even a few extra pounds," Baker said.

For example, a 4-foot-1-inch boy who weighed 61 pounds at age 7 faced a 12 percent higher risk of heart disease between ages 25 and 71, compared with a similar boy who weighed a normal 52 pounds.

The greatest increased risk was for the heaviest older children. Risk was lower for those who were overweight at age 7 but not at 13, indicating that a child who can lose excess weight while still young, and maintain normal weight, can reduce the excess risk.

In the second study, Kirsten Bibbins-Domingo of the University of California at San Francisco used various data to project that by the time today's adolescents turn 35 in 2020, up to 37 percent of men and 44 percent of women will be obese, resulting in 100,000 more cases of heart disease by 2035. The projections would have been higher if the Danish data had been included, she said: "We took a very conservative approach."