June 4, 2002 -- Breast milk may be best for many reasons, but making your baby smarter is not necessarily one of them. A comprehensive review of research on the subject reveals that while several studies have shown a link between breastfeeding and intelligence in infants, most of those studies don't hold up to widely accepted research standards.
"Although the majority of studies concluded that breastfeeding promotes intelligence, the evidence from higher-quality studies is less convincing," write the authors of the review, which appears in the June issue of Pediatrics.
The researchers looked at 40 studies published between 1929 and February 2001, and found that 68% concluded that breastfeeding promotes intelligence. But many studies had flaws in how they were designed and conducted, and only two passed a test based on eight principles of scientific research. Of those two studies, one showed that breastfeeding had a positive effect on intelligence and the other did not.
The problem is that it's nearly impossible to conduct a strong, rigorous scientific study when it comes to breastfeeding. The best medical research studies involve randomly assigning each person to receive a treatment or no treatment (often in the form of a placebo).
And since most people in the medical field believe that breastfeeding is best, it's neither feasible nor ethical to withhold breastfeeding from some mothers and infants.
"Therefore, the environment and the mothers of the breastfed children are inherently different from those infants whose mothers either choose not to breastfeed or experience difficulty breastfeeding," the researchers write.
Lead researcher Anjali Jain, MD, from the University of Chicago's department of pediatrics, and colleagues say one of the biggest problems they found with most of the studies was that the investigators did not rule out other potential factors that affect intelligence -- such as socioeconomic status and how much stimulation the child received.
Aside from the two "best" studies, the seven other studies that took these factors into account also came up with conflicting results. Three showed breastfeeding promotes intelligence and four did not.
The authors say more rigorous research is needed to further examine the relationship between breastfeeding and intelligence. But whether or not a conclusive link is ever found, researchers agree that breastfeeding provides a host of other benefits -- including fighting infection and promoting a stronger bond between mother and child -- although the strength of these associations may be hard to measure in scientific terms.
For example, a study last month in The Journal of the American Medical Association showed that breastfed babies had higher IQs as adults, and the recommended six months of nursing significantly reduces lung and ear infections in babies.
Experts say breast milk contains essential fatty acids and other nutritional elements that may play a role in providing these benefits.
But they also point out that infant formulas have come a long way from those used more than 50 years ago, when some of the first studies were conducted. Now, infant formula more closely resembles breast milk and has been fortified with many of these vital nutrients to promote healthy development.
Most recently, the FDA has allowed manufacturers to add the fatty acids DHA and ARA -- which are important for infant brain and eye development and occur naturally in breast milk -- to their infant formulas sold in the U.S. The first of these fortified formulas appeared in stores earlier this year.