April 24, 2007 -- Breastfed babies are just as likely to grow up to be overweight adults as babies who are bottle fed, new research shows.
Results from a study involving more than 35,000 female nurses seem to contradict earlier research, which prompted government health officials to recommend breastfeeding as a strategy for reducing childhood obesity.
There was a suggestion of a protective effect during early childhood, but no link was seen between breastfeeding and body weight after age 5, says Harvard Medical School associate professor Karin B Michels, PhD.
“Even if breastfeeding is protective very early in life, this does not appear to carry through to adolescence and adulthood,” Michels tells WebMD. “We certainly encourage breastfeeding, which has many positive consequences for both mother and child. But it should not be promoted as a solution for either the childhood or adult obesity epidemic.”
12.5 Million Overweight Kids
According to CDC figures from 2003-2004, 12.5 million kids between ages 2 and 19 are overweight.
Though it is clear that breastfed infants tend to gain weight more slowly during the first year of life, the link between breastfeeding and body weight later on is much more uncertain, Michels says.
The latest study is the first attempt to examine the residual impact of breastfeeding on body weight until age 40.
A total of 35,526 female nurses participating in the larger Nurses Health Study II were followed from 1989 until 2001, and their mothers were surveyed to determine if the nurses where breastfed during infancy and, if so, for how long.
Nurses exclusively breastfed during the first six months of life were no less likely to be overweight or obese during adulthood as those who were bottle fed during infancy.
A slight association was seen between infant breastfeeding and lower body weight up until age 5, but it was not significant, Michels says.
The study appears in the latest online issue of the International Journal of Obesity.
‘Jury Still Out’
Michels says public health messages that encourage breastfeeding as a strategy for reducing later obesity overstate the case for a protective benefit.
But the chief of the nutrition branch for the CDC disagrees.
Though there is little evidence that protection lasts until adulthood, Laurence Grummer-Strawn, PhD, says the research as a whole continues to support a protective role for breastfeeding, at least in early life.
“The best evidence we have indicates that the [protective] effect probably diminishes over time, and that is what this study shows,” he tells WebMD. “It is not very surprising that the evidence would fail to show a benefit for breastfeeding 40 years later.”
Women in the U.S. who breastfeed tend to be better educated and more economically advantaged than women who choose not to breastfeed their babies. They also tend to lead healthier lifestyles, with the assumption that they promote healthier behaviors in their children.
Grummer-Strawn acknowledges that these socioeconomic influences may explain the link between breastfeeding and lower childhood body weight. But even if this proves to be the case, there are still plenty of good reasons to breastfeed.
“The jury is still out on whether there is a causal relationship (between breastfeeding and childhood body weight),” Grummer-Strawn says. “The CDC continues to promote breastfeeding for a number of health reasons, including the possible prevention of overweight in children.”