Children who are breastfed longer do not appear to be less likely to be obese or overweight, findings that are contrary to previous evidence that had suggested that breastfeeding may have a protective effect against child obesity, according to a study published today in JAMA.
Observational studies comparing the children of women who chose to breastfeed with those who did not suggested that breastfeeding is associated with a lower likelihood of overweight in childhood. However, such observational studies have certain weaknesses that cast uncertainty on any apparent associations. For example, there often are important differences between women who choose to breastfeed and those who don’t, such as higher educational levels, that might explain the differences. Additionally, an array of factors contribute to weight, including social and environmental factors, making it difficult to identify a single cause.
To help tease out the role that breastfeeding might play in childhood obesity, researchers analyzed data from a clinical trial in which 31 maternity hospitals in Belarus were randomized either to an intervention to promote long-term and exclusive breastfeeding or to the usual breastfeeding promotion practices. Ultimately, the trial enrolled 17046 mother-child pairs between 1996 and 1997 and has followed up with the children all the way to age 11.5 years. Women who received the new breastfeeding intervention were much more likely to breastfeed exclusively at 3 months (43% vs 6%) and 6 months (7.9% vs 0.6%). Children in the intervention group were not less likely to be overweight or obese. In addition, the findings were consistent with analysis of the 2 groups at 6.5 years of age. Evidence from a well-conducted randomized controlled trial is considered stronger than that from observational studies.
Richard Martin, MD, PhD, professor of clinical epidemiology at the University of Bristol, discussed the findings with news@JAMA.
news@JAMA: What distinguishes the Belarus study from observational studies of breastfeeding?
Dr Martin: By randomizing, we can look at the long-term benefits of breastfeeding without the usual confounding present in observational studies because it wasn’t a choice for the mum. The large contrast [between the 2 groups of women] allows us to make inferences about the long-term effects of breastfeeding.
news@JAMA: What evidence had led to the belief that breastfeeding might reduce obesity later in life?
Dr Martin: There are a large number of observational studies looking at moms who have chosen to breastfeed compared with those who don’t that follow the children in terms of growth. The problem with those studies is that they are not based on randomization and there is a strong potential for confounding.
Breastfeeding for a long time is difficult. Women who choose to do so are often different from those who don’t. In the United Kingdom—this is probably true in the United States as well—education level plays a big part. In low- and middle-income countries, breastfeeding is not associated with education, and in those countries, you don’t see a relationship between breastfeeding and obesity. So is it breastfeeding or other factors causing an apparent link with obesity?
news@JAMA: Did your study find potential benefits of breastfeeding?
Dr Martin: Based on our analysis of the intervention vs control arm, we found that those children in the intervention arm had a lower risk of gastrointestinal tract infections and atopic eczema in the first year of life. At 6.5 years of life, those in the breastfeeding arm had higher scores on IQ, so better cognitive development was seen in the breastfeeding group. The trial has provided strong evidence of these benefits.
One caveat is that the intervention promotes duration and exclusivity amongst mothers who intend to breastfeed. Every mother in the trial intended to and initiated breastfeeding. Our study groups compared mothers who practiced longer exclusive breastfeeding against those who didn’t breastfeed for so long. In observational studies, they are often comparing ever vs never breastfeeding. We can’t answer the question about whether ever breastfeeding has a protective effect vs never breastfeeding. We can only answer the question about longer exclusive breastfeeding.
news@JAMA: What are the next steps for the study?
Dr Martin: We are currently following up with the children at 16.5 years to assess difference in vision, lung function, and cognitive development between the groups. We also are repeating the exam for atopic eczema.
news@JAMA: What do you think are the implications of these findings for clinicians and women?
Dr Martin: It doesn’t appear that breastfeeding will reduce the obesity epidemic, but our study does provide ample evidence of other benefits of breastfeeding that support continued promotion of the practice. In terms of policy to reduce overweight and obesity, we should turn our attention to other interventions that promote healthy eating and making the environment less likely to promote obesity.