The long-term benefits of breastfeeding, such as higher IQ and protection from a variety of diseases, may have been overstated by past research.

Although breastfeeding naturally provides the best nutrition to infants, sociologists Cynthia G. Colena and David M. Ramey reported this month in the journal Social Science & Wellbeing that some purported health benefits are based on flawed data. In a study of more than 8,000 American children, the researchers compared life outcomes among siblings as a better look at the effects of breastfeeding, given that so many other variables change from family to family. Past studies had failed to account for a high selection bias in breastfeeding, with “choosier moms” choosing to breastfeed -- along with other healthful and helpful behaviors.

For the truest comparison, they examined population data from nearly 1,800 pairs of siblings whose mother breast-fed one and bottle-fed the other. The researchers used longitudinal data to look at 11 health outcomes previously shown influenced by breastfeeding, including body mass index, hyperactivity, math and reading skills, among others.

“Once we restrict analyses to siblings and incorporate within-family fixed effects, estimates of the association between breastfeeding and all but one indicator of child health and wellbeing dramatically decrease and fail to maintain statistical significance,” the researchers said in a statement. “Our results suggest that much of the beneficial long-term effects typically attributed to breastfeeding, per se, may primarily be due to selection pressures into infant feeding practices along key demographic characteristics such as race and socioeconomic status."

Colena and Ramey designed the study to mimic a natural experiment determining the effects of breastfeeding, with all else equal. Whereas findings from standard multiple regression models yielded improved results for the breastfeeders, bottle-babies did just about as well, the difference deemed statistically insignificant.

However, the findings don’t challenge notions about the short-term health benefits to breastfeeding, which include greater protection from gut and chest infections. The study only questions the purported benefits of later outcomes with regard to obesity, asthma, hyperactivity, scholastic success, and the strength of parental bonds. Still, many breastfeeding advocates emphasize the broader range of health benefits confered to mother and child, also noting that short-term health serves as the foundation for later wellbeing. The benefits to breastfeeding are myriad, says Seana Rowell, a stay-at-home mother (and blogger) presently staying on New York City's Upper East Side.

"Regardless of whether the benefits into adulthood can be confirmed, or even tracked, the benefits to the infant and toddler are clear. Palate development, teeth, ability to recover easily from illness, social and developmental aid through toddler years; all benefits of breastfeeding," she told Medical Daily by email. "It stands to reason that a healthier beginning in life would impact all stages of growth and development."

Other breastfeeding advocates on Facebook questioned the study's finding, suggesting the small cabal of baby formula manufacturers might have had something to do with it. In fact, the study was funded by a grant to Ohio State University by the U.S. government's Eunice Kennedy Shriver National Intitute of Child Health and Human Development.

Source: Colen, Cynthia G., Ramey, David M. Is Breast Truly Best? Estimating The Effects Of Breastfeeding On Long-Term Child Health And Wellbeing In The United States Using Sibling Comparisons. Social Science & Medicine. 2014.