Midlife Weight Loss Cuts Heart Risk

Being overweight as a teenager carries a greater risk of being an overweight adult, along with an increased risk of dying of heart disease. But overweight adolescents who slim down in middle age may lower their risk, a new study shows.

Previous studies have linked being overweight as a teenager or young adult to deadly consequences later in life, including an increased risk of heart disease. But it was unclear if the risk was higher simply because heavy teenagers become heavy adults, or because being overweight or obese as a young adult causes irreversible damage.

To find out, a team of scientists at Harvard Medical School and elsewhere combed through data from the Harvard Alumni Health Study, which tracked the medical information of men who entered the university as freshmen from 1916 to 1950. The researchers gathered data on about 19,000 of the Harvard alumni who were subsequently followed in later decades, looking at their habits, heart disease risk histories and body mass indexes, among other things. The subjects were followed for up to 82 years.

The study, published on Monday in The Archives of Internal Medicine, found that the heaviest students were more likely to become overweight or obese adults. Furthermore, the men who were obese as freshmen had nearly twice the risk of dying of heart disease decades later as the men who had been of normal weight in college. A similarly increased risk was seen among the men who were overweight as freshmen.

“That simply reflects the fact that fat kids become fat adults,” said Dr. I-Min Lee, an associate professor of medicine at Harvard Medical School and an author of the study, “and that drives deaths from heart disease.”

But when the researchers factored in middle age, adjusting for the subjects’ weight at that time, they found that the risk changed. The men who started college overweight or obese but were of normal weight in middle age no longer had a higher risk of dying of heart disease.

Body mass index in middle age was a strong predictor of dying of heart disease, the study showed. Being overweight in middle age increased the risk 25 percent, and being obese raised it 60 percent.

While the study looked only at men, Dr. Lee said she believed the findings would hold for women as well, since the biological effects of overweight and obesity on heart disease risk are similar in the two sexes. In both men and women, the data linking obesity in middle age to heart disease is clear, she said.

The only other study that prospectively measured B.M.I. in both early and later life, published over 20 years ago, showed that a higher body weight in adolescence raised the risk of heart disease later in life, regardless of B.M.I. in midlife. But that study was considerably smaller and looked at only about 500 people.

Dr. Lee said that while the latest study offered good news, “it’s not that it’s not harmful to be fat when you’re younger,” since extra weight in adolescence tends to follow you into adulthood. But an editor’s note that accompanied the study ended on a more optimistic note, saying it “brings us some reason for hope that efforts to address childhood obesity are well worth it.”

“The negative influence of early B.M.I. on mortality drops out when middle-age B.M.I. is added,” the note went on. “It is never too late to adopt healthy lifestyle changes.”