May 16, 2001 Boston, MA — More months on breast milk as infants may mean fewer pounds on older children and teens later, according to a Harvard Medical School study in the May 16 issue of the Journal of the American Medical Association.
"This study suggests that breast-feeding may prevent obesity later in life," says lead author Matthew Gillman, MD, associate professor at Harvard Medical School and Harvard Pilgrim Health Care. "Our study, along with others, supports the recommendation of the American Academy of Pediatrics to breast-feed infants for the first year."
Obesity has risen dramatically among children and adults. Overweight teens tend to have higher blood pressure and cholesterol, lower self esteem, and on average fare less well in school and earn less as young adults. They also are much more likely to grow into obese adults who face serious health consequences, such as heart disease, diabetes and arthritis.
"Once present, obesity is hard to treat," Gillman says. "For these reasons, prevention is paramount."
Gillman and his colleagues analyzed questionnaires filled out by 8,186 girls and 7,155 boys ages 9 to 14 in the Growing Up Today Study. About 5 percent of the girls and 9 percent of the boys were overweight, defined as having a body mass index (weight divided by height squared) greater than 95 percent of children of the same age and sex. That’s slightly lower than found in the general U.S. population.
When the researchers questioned the mothers – all part of the Nurses’ Health Study II – they found that 62 percent of the children were only or mostly fed breast milk for the first six months of life, while 31 percent were only or mostly fed infant formula. Just less than one-half were breast-fed for at least seven months, and about one-third were breast-fed for three months or less. Nationally, less than 30 percent of infants are breast-fed for at least 6 months.
Among the mostly breast fed, about 4 percent of the girls and 7 percent of the boys were overweight compared to the 6 percent of the girls and 11 percent of the boys fed mostly infant formula. Among those who were breast fed for seven months or more, about 4 percent of the girls and 7 percent of the boys were overweight compared to about 6 percent of girls and 12 percent of boys who drank breast milk for three months or less.
The researchers statistically adjusted the results for age, gender, sexual maturity, total calorie intake, physical activity, time watching television, mothers body mass index, and other social, economic and lifestyle factors known to influence weight. In this study, breast-feeding includes women who fed infants breast milk extracted from breast pumps.
The adjusted figures show that infants who were breast-fed more than formula fed or who were breast-fed for longer periods had approximately 20 percent lower risk of being overweight in the preteen and teen years.
The results make biological sense, Gillman says. Breast-feeding could protect against later obesity by providing infants more control over when and how much they consume—when they’re full instead of when a bottle is empty, for example—which could shape future eating behavior. Also, breast milk itself might provide early "metabolic programming," leading to less fat accumulation, for example. Gillman would like to see further studies among more representative samples of the U.S. population.
"Breast milk is already acknowledged as the best food for infants," says William Dietz, division of nutrition and physical activity, Centers of Disease Control and Prevention, in an accompanying editorial. "The increased initiation and duration of breastfeeding may also provide a low-cost, readily available strategy to help prevent childhood and adolescent obesity."
The study was funded by the National Institutes of Health, Harvard Medical School and the Harvard Pilgrim Health Care foundation. Gillman was a Robert Wood Johnson Generalist Faculty Physician at the time this work was performed.
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