Teenagers who are overweight — or even just at the high end of normal weight — are at increased risk for developing heart disease when they become adults, even if they don’t grow up to be overweight, researchers reported Wednesday.

In the first study of its kind, an analysis of more than 37,000 teenagers found that the more they weighed when they were 17 years old, the greater their likelihood of having started to develop heart disease by the time they reached their 30s or 40s.

But the teens’ weight had far less influence on their risk of developing diabetes later in life, the researchers reported in a paper being published in the New England Journal of Medicine.

While previous studies have indicated that being overweight in adolescence increases the chances of developing heart disease, this study is the first to carefully document the risk and to show that the danger is independent of adult weight. In contrast, only those who were also overweight in adulthood were more likely to develop diabetes, the study showed.

“This shows that for cardiovascular disease, you are going to pay the price for a higher weight in those early years later in life, even if you adopt a better lifestyle and are not overweight when you get older,” said Amir Tirosh of the Harvard School of Public Health in Boston, who led the analysis. “This should be another alarming red flag for pediatricians, given the alarming rates of obesity and overweight in kids.”

Other researchers agreed, saying the findings should add to the urgency to get children to watch their weight, eat well and exercise regularly.

“This is a landmark study,” David S. Ludwig, a childhood obesity expert at Children’s Hospital Boston, said in an e-mail.

The findings indicate that being heavy in adolescence “may produce permanent changes in the body” that increase the risk of heart disease for the rest of an individual’s life, such as causing an early buildup of plaque in arteries supplying blood to the heart, Ludwig said.

“The findings speak to the great public health importance of addressing excessive weight gain in adolescence instead of postponing action to later in life,” he said.

Other researchers concurred but cautioned against the findings making parents worry too much about children who are not overweight.

“This doesn’t mean children and adolescents have to be extremely thin. We don’t want a preoccupation with leanness leading to eating disorders,” said JoAnn E. Manson, chief of preventive medicine at Brigham and Women’s Hospital in Boston. “But we can’t be complacent about obesity and overweight in adolescence.”

The findings come as many schools are sending children home with report cards documenting their weight, and the study could help parents recognize potential problems early, experts said.

“When somebody gets sent home with a grade card with a BMI that someone thought no one needs to be concerned about because it is quote, ‘normal,’ unquote, this says it might really be a wake-up call that that individual should be paying more attention to their health,” said George Blackburn, associate director of the division of nutrition at Harvard Medical School.

For the study, Tirosh and his colleagues analyzed data collected from 37,674 healthy young Israeli males who had their weight and health carefully documented with physical examinations conducted by the Israeli Army Medical Corps beginning at age 17.

The risk for heart disease began to increase for those who had a body mass index (BMI) above 20.7, which is still considered well within a healthy weight, the researchers found. (For instance, a 5-foot-8-inch male who weighs 142 pounds would have a BMI of 21.) Those with a BMI above 20.7 were about three times as likely to develop heart disease by the time they were in their 30s or 40s. Those with a BMI above 25 — considered the threshold between normal weight and overweight — were seven times as likely. That held true even for those who, as adults, were at weights considered healthy.

Heart disease was defined as a narrowing of at least 50 percent in one major artery supplying blood to the heart.

The risk for heart disease increased 12 percent with every one unit of increase in BMI, the study found. In contrast, while the risk for diabetes increased 10 percent with every rise of one unit of BMI, teenage weight had no effect on the risk for diabetes among those who were not overweight in adulthood.

Although the study involved only males, Manson said previous studies have produced evidence that suggests the results would hold true for females, as well.