April 6, 2011 -- Researchers have long known that overweight or obese kids are more likely to grow up to be heavy adults, and as overweight adults, to be more likely to develop significant health problems associated with excess body weight, including cardiovascular disease and diabetes.
Now a new study published in The New England Journal of Medicine has added a significant wrinkle to the problem of growing childhood girth.
The study, which followed more than 37,000 teenage boys into their 30s, shows that some of the risks associated with being an overweight teenager apparently don’t go away, even if a person loses weight later in life.
“Cardiovascular disease really is a pediatric illness. It begins in childhood,” says Peter T. Katzmarzyk, PhD, professor and associate executive director for population science at the Pennington Biomedical Research Center in Baton Rouge, La.
“Even if you change your behavior, there’s still this carryover effect that being obese or overweight as an adolescent seems to really last into adult health,” says Katzmarzyk, who was not involved in the study.
What’s more, researchers found that the risks appear to rise at body mass indexes (BMIs) that are considered to be well within the normal range. Body mass index is a measurement that relates weight to height.
“The risk goes up significantly for diabetes with a BMI value of 22.3 and for cardiovascular disease above a BMI of 20.9 and above,” says study researcher Amir Tirosh, MD, PhD. Tirosh is a fellow in the department of medicine, division of endocrinology, diabetes, and hypertension at Brigham and Women’s Hospital in Boston.
A male who stands 5 feet 6 inches and weighs 130 pounds has a BMI of 21, for example.
Teens who had BMIs higher than 25, which is the threshold for overweight, had nearly three times the risk of developing diabetes and nearly eight times the risk of having heart disease as young adults, compared to the lightest group, which averaged 5 feet 6 inches in height and weighed about 114 pounds.
Diabetes Risks May Be Changed
In contrast with what happened with heart disease in the study, researchers found that diabetes risk could be more malleable. That is, if heavy teens lost weight as adults, their risk of getting type 2 diabetes was erased.
“This is the good news, actually, of the study,” Tirosh says. “For those who would not grow up to become overweight or obese, the risk is completely reversible.”
Though the study had some limitations, including the fact that it didn’t include girls, experts say the finding was significant.
“I think it’s a very interesting and important study,” says Stephen R. Daniels, MD, PhD, chairman of the department of pediatrics at the University of Colorado Denver School of Medicine. Daniels is also pediatrician-in-chief at Children’s Hospital, Denver.
“One of the things we’ve been lacking is this longitudinal look at what happens in childhood and adolescence and how that plays out in adulthood in terms of the kind of outcomes they were looking at,” says Daniels, who co-authored an American Heart Association scientific statement on obesity in children but was not involved in the current research.
“Our approach to looking at BMI in children has always been a statistical approach, meaning that we took a population and assumed that it was the people at the upper end of that distribution where the problems were,” Daniels says. “We’ve never really had a good outcome-based definition of body mass index in children.”
Tracking Heart and Diabetes Risk
Researchers followed more than 37,000 Israeli young men who received health screenings at age 17 when they signed up for their country’s mandatory military service.
They continued to get checkups every three to five years until they were in their early to mid-30s.
After an average of 17 years, researchers documented nearly 1,200 cases of type 2 diabetes and 327 cases of cardiovascular disease, which was defined as having at least one coronary artery at least 50% blocked.
Looking back at the men’s BMIs when they first started the study, researchers saw a clear link between their size and their risks for both diabetes and heart disease.
Average BMIs in the study ranged from 17.4, representing an average height of 5 feet 6 inches and a weight of 114 pounds, in the lightest group, to 27.6, representing an average of 5 feet 8 inches and 185 pounds, in the heaviest group.
Those who fell into the heaviest group had about three times the risk of developing diabetes compared to the lightest teens.
For every point increase in BMI in the teens, the risk of developing type 2 diabetes as an adult increased by nearly 10% from the lowest to highest groups.
But that risk disappeared after researchers adjusted the results to reflect adult BMIs.
For heart disease risk, however, which increased 12% for every point increase in BMI, the association remained, even if the men had lost weight as adults.
“It seems to be that our body has a longer BMI memory in terms of cardiovascular diseases,” says Tirosh.
“For two 35- or 40-year-old men who have a normal BMI as adults, let’s say BMI of 22 or 23, one could have as much as a sevenfold higher risk for cardiovascular disease, simply because he used to have a higher BMI as a teenager,” Tirosh tells WebMD.
Experts say the message of the study to parents and teens should be clear.