Sibling Study Finds No Long-Term Breastfeeding Benefits For Kids
When Ohio State sociologist Cynthia Colen embarked on the biggest study yet of the long-term effects of breastfeeding, she expected it to yield still more evidence of “breast is best.”
Her research focuses on the health gaps between rich and poor, and she anticipated findings that would underscore the high price paid by poor and working-class mothers, whose jobs often stand in the way of breastfeeding.
But the data did not go there.
Previous research had reported a variety of long-term breastfeeding benefits in children, ranging from slightly higher IQs to lower risks of Attention Deficit Disorder. But those studies had mainly compared children across different families.
Dr. Colen’s study, published in the journal Social Science & Medicine, looked at thousands of siblings within families, comparing those who were bottle-fed to those who were breastfed.
And all the previously reported long-term benefits evaporated.
“I was shocked,” she said. “I thought, ‘Of course there’s going to be some confounding. We know that children who are breastfed are much more likely to come from middle-income families; to have parents with higher levels of education; they’re more likely to be white; more likely to live in middle-class or safe neighborhoods — all these things that we know are going to impact these long-term child outcomes.' But I didn’t expect such a dramatic reduction.”
So, in this study spanning 25 years of data on more than 8,000 children ages 4 to 14, the long-term benefits of breastfeeding dwindled down to virtually nothing?
Yikes. It takes courage to question breastfeeding benefits these days. So let’s be clear: Dr. Colen is by no means against breastfeeding. On the contrary. And the evidence for the short-term benefits of breastfeeding is overwhelmingly clear, from improved immunity for the baby to healthier weight for both baby and mother. But, she says, “We need to just get a more balanced conversation going.”
“I’m not saying that women shouldn’t breastfeed and I’m not saying that breastfeeding is not beneficial,” she said. But “I think we have to be honest and try to understand more about what breastfeeding can and cannot do for women and their children, and to start to expand the conversation to these larger social and economic factors that we need to address.”
Those social and economic factors include the need for better maternity leaves and more affordable daycare — as well as higher school quality, safer neighborhoods, more family-friendly jobs. Dr. Colen argues for taking a more careful look at what happens in a child's life beyond infancy, and for understanding that breastfeeding may be difficult to the point of impossibility for some groups of women. (Interesting paper: Is Breastfeeding Truly Cost-Free?)
"Rather than placing the blame at their feet, let’s be more realistic about what breast-feeding does and doesn’t do,” she says in a press release.
So what are the findings, exactly?
Using nationally representative survey data from 1986 through 2010, Dr. Colen and co-author David Ramey analyzed 11 key indicators in children from ages 4 to 14. From academic scores to behavior to obesity, they found no advantages for breastfed over bottle-fed siblings. The sample included 1,773 siblings in which at least one was breastfed and at least one was not.
How could this be? Haven’t we been hearing for years that breastfeeding makes children smarter, healthier, all-around better?
Yes, but it would seem that many of those studies may have been skewed by what Prof. Colen’s field — sociology — calls “residual confounders.” That is to say: The researchers tried to factor in socio-economic elements like income and race, but they must not have done enough to offset them.
The more educated and better off a woman is, the likelier she is to breastfeed. Being better off is also linked to myriad desirable outcomes, from healthier weight to better test scores. The previous studies tried to correct for that overlap. No single study is the final word on a complex topic like this, but if this study is right, the previous studies failed to clean out their "residual confounders."
So how do we know that all the studies on shorter-term benefits of breastfeeding didn't make that same mistake?
The results of those studies look more convincing, Dr. Colen said. "The effect sizes are larger, and there's more of a known biological pathway. We know moms are able to pass immunity through breast milk to babies, and that in the very short term, it makes sense biologically that this boosted immunity can protect their intestines or their lungs from infections. But this is likely to wear off fairly quickly during that first year."
And mightn't this sibling study be confounded somehow as well? Dr. Colen says there have been two previous studies that looked at siblings and breastfeeding benefits.
"The other two studies did show remarkable reductions [in long-term benefits] when they did their sibling comparisons," she said. "So in that way, our studies were similar. I think our study went a little bit further in showing how much the effect of breastfeeding was reduced when you went from between-family comparisons to an in-family comparison."
Personal note: I'm torn. I like the prospect that this study will give some solace to women who cannot breastfeed, or who give up breastfeeding earlier than the recommended one-year mark. (And it helps explain why the generation born when bottle-feeding was most promoted, in the 1950s and 1960s, is not noticeably disadvantaged.)
But I also hate to potentially undermine breastfeeding in a society where, in the big picture, it still needs more support. I offered the final word to Dr. Joan Meek, a member of the American Academy of Pediatrics' section on breastfeeding.
She raised the possibility that perhaps many of the mothers in the study who breastfed did not do it for long enough to reap full benefits. The women who breastfed in the study did so for an average of 23 weeks.
"When you look at what the American Academy of Pediatrics as well as the CDC and multiple other organizations say in terms of optimal breastfeeding, it's about six months of exclusive breastfeeding and then a minimum of one to two years total duration," she said. "And when you look at the long-term benefits, you really have to look at that exclusivity and that total duration of breastfeeding to see those differences."
From reducing risks of diabetes to childhood cancer, she said, "there are compelling data that exclusive breastfeeding and total duration of breastfeeding are the keys, not just any breastfeeding."
Ultimately, Dr. Meek said, "The preponderance of evidence, using well-controlled studies, would demonstrate that there are long-term benefits to breastfeeding, particularly when we look at exclusive breastfeeding for about six months, and longer duration of breastfeeding." And, there are maternal benefits as well: lower risk of breast cancer, ovarian cancer, obesity, diabetes, possibly — the evidence is still preliminary — even of arthritis.
But in many cases, "there's dose dependency," she said. "The longer the breastfeeding, the longer the exclusive breastfeeding, the less risk you will experience."
Further reading: The Case Against Breastfeeding, by Hanna Rosin in The Atlantic
Postscript in response to social media queries: No, Dr. Colen's study was not funded by formula makers. According to the Ohio State press release: "This work is supported by a grant from the Eunice Kennedy Shriver National Institute of Child Health & Human Development awarded to the Ohio State University Institute for Population Research."