WASHINGTON — Babies who are breast-fed are less likely to become severely overweight as they grow through childhood, according to a major study released Tuesday.
The study of more than 15,000 preadolescents found that those formula-fed as infants were 22% more likely than breast-fed babies to be obese or overweight by the time they reached ages 9 to 14. The study, conducted by Harvard University researchers, also found that the longer an infant was breast-fed, the less likely he or she would be overweight.
A second study of 2,685 younger children ages 3 to 5 by researchers at the National Institutes of Health also found that breast-feeding might help to reduce the risk that children would become overweight but concluded the effect was minor.
Nevertheless, taken together, the two studies offer compelling evidence that breast-feeding helps protect against weight problems later in life, other researchers said.
"These studies offer another good reason to breast-feed--it reduces the risk of overweight in the child," said William Dietz of the federal Centers for Disease Control and Prevention, who wrote an editorial accompanying the studies in Wednesday's Journal of the American Medical Assn.
"The effect may not be terribly large," he said. "But we don't have many good strategies to combat the epidemic of obesity we're seeing."
Medical and public health officials have long advocated breast-feeding because of its proven health benefits for children, and possibly mothers too. These two studies--among the largest ever undertaken on the subject--are the first in the United States to find a connection between breast-feeding and protection against becoming overweight.
The prevalence of breast-feeding has increased in the last decade, and almost 65% of mothers nurse their infants during the first week of life. But federal statistics show that only 29% of infants are still breast-fed at 6 months--the minimum amount recommended by the American Academy of Pediatrics.
While Dietz of the CDC hailed the studies as indicating that "breast-feeding has a protective effect against obesity," the lead researchers of the two studies disagreed over the implications.
Matthew Gilman of the Harvard Medical School said that the results showed that breast-feeding, even for a short time, had a positive impact on the child's later weight. He said the fact that the children in his study were already preadolescents gave him greater confidence that the connection was scientifically sound.
But Mary Hediger of the National Institute of Child Health and Human Development at the NIH said her research did not show a strong link between formula-feeding and the heaviest children in her study. In addition, she did not find that length of breast-feeding had an impact on later weight. The most important factor is the weight of the mother, she found.
"If mothers think they can let their kids sit in front of the TV and eat McDonald's because they were breast-fed when they were babies, they're wrong," she said.