Breastfed children do display slightly less hyperactivity at age 3, but that positive effect appears to disappear by the time the children turn 5, the study also found.
These findings shouldn’t, however, discourage women from breastfeeding, the authors of the study stress. Breastfeeding is strongly associated with many health benefits, which include a lower risk of infections and sudden infant death syndrome (SIDS) for the child and a lower risk of breast and ovarian cancer for the mother.
But the new findings may offer some reassurance to mothers who find themselves unable to breastfeed.
An age-old debate
The long-term effects of breastfeeding on children’s intelligence and behavior have been debated for decades. Some studies have found such effects. Others haven’t.
To have a truly definitive study on the benefits of breastfeeding, mothers would have to be randomly assigned to either breastfeed or not breastfeed their child from birth. That, of course, is not feasible. (It also may not be ethical, given the known health benefits associated with breastfeeding.) So researchers rely on observational studies instead, ones that retrospectively compare various outcomes for groups of breastfed and non-breastfed babies.
But there’s a major problem with that approach. The outcomes in observational studies can be influenced by many confounding factors. Research has shown, for example, that women who breastfeed their babies tend to have more education and a higher socioeconomic status than women who don’t breastfeed — factors that could be contributing to the better outcomes for their babies.
Researchers try to adjust their findings for such confounding factors, but it’s not always possible to do so.
A new approach
For the current breastfeeding study, the researchers took a somewhat novel approach. They used a relatively new statistical method known as propensity score matching, which enabled them to match breastfed and formula-fed babies with similar confounding factors.
The children — about 8,000 — were randomly selected from the government-funded Growing Up in Ireland study, which has been following the progress of about 17,000 Irish children and youth since 2006. All the children selected for the breastfeeding study were born between a six-month period in late 2007 and early 2008.
The researchers gathered information about whether the babies had been breastfed — and for how long — from questionnaires filled out by the mothers. (About 60 percent of the babies were breastfed at least partially for up to a month, while 40 percent were breastfed at least partially for between one and six months. Only about 5 percent of the babies were breastfed for more than six months.)
The researchers also collected the results of tests given to the children to assess their cognitive abilities — specifically problem-solving and vocabulary — at ages 3 and 5 years. The data also included assessments of whether the children were demonstrating any problem behaviors at those years.
Then, using the propensity score matching, they matched the breastfed and nonbreastfed groups of babies for more than a dozen confounding factors that might affect a child’s cognitive skills and behavior, such as the baby’s gender and weight at birth, the family’s socioeconomic status and the presence of siblings in the household.
After all that data was analyzed — particularly after the groups were matched for confounding factors— the researchers found no statistically significant difference in cognitive skills at age 3 or 5. They did find that the breastfed children were less likely than nonbreastfed children to display hyperactive behavior at age 3, but the difference was small and had faded away by age 5.
Not the final word
This study has its own limitations. Most notably, the information on breastfeeding was collected from the mothers retrospectively and, therefore, may not have been accurate. In addition, reports about the children’s behavior were collected only from the parents when the children were 3, unlike the reports at age 5, which came from parents and teachers. Other research has shown that parents tend to rate their children’s behavior more problematic than others.
This study is not likely to end the debate about the possible cognitive and behavioral benefits of breastfeeding, therefore. But it appears to be one of the better-designed studies to date on the topic.
FMI: You can read the study in full online at the Pediatrics website.