Eager to encourage more women to breastfeed, public health officials and some doctors have exaggerated the benefits of breastfeeding. In parenting magazines, on the Dr. Sears website, in public advocacy campaigns, and even in hospital handouts I have read that breastfeeding reduces the risk of ear infections, respiratory tract infections, gastrointestinal infections, necrotizing enterocolitis, asthma, allergies, eczema, ADHD, dental cavities, atopic dermatitis, diabetes, Crohn's and celiac disease, obesity, cardiovascular disease, high blood pressure, sudden infant death syndrome, and some cancers. It is also said to boost intelligence and maternal attachment.
Medical science is much less certain of the benefits of breastfeeding. Much of the research in this field is characterized by scientists as "weak" and "inconclusive." It is weak because all of the research on the effects of breastfeeding is observational. Rather than sorting women randomly into breast and formula feeding cohorts, researchers compare health outcomes among children who have been breastfed or formula fed. But women who choose to breastfeed are different than women who choose not to in many other ways. They are in higher socioeconomic brackets, they have completed more education, they are less likely to smoke, and less likely to send their children to daycare. Any one of these "confounding factors" could account for differences in health outcomes, but most of the older research into breastfeeding outcomes did not control for those confounding factors. And because the research is "weak," it is also often "inconclusive." Some studies find evidence of a correlation, others do not, and we don't know which results are accurate.
Still, some of the newer breastfeeding research is better, and offers some purchase. There is strong evidence that breastfeeding offers some protection against infections, including ear, gastrointestinal and respiratory infections and a rare condition called necrotizing enterocolitis that affects some premature babies. That protection, however, is fairly modest. As Dr. David Meyers, the director of the U.S. Agency for Healthcare Research and Quality pointed out, six women would have to breastfeed exclusively for six months to prevent one ear infection. At least 26 women will have to breastfeed exclusively for four or more months to prevent one case of pneumonia. That's about 5400 hours of breastfeeding to prevent one ear infection, or 15,600 hours to prevent a case of pneumonia.
The correlation between breastfeeding and SIDS is also well established. But whether it is driven by breastfeeding, or by "factors associated with breastfeeding" has yet to be determined. For years SIDS experts insisted it was the former, and if it is actually breastfeeding that makes the difference, scientists have yet to discover how. One hypothesis is that the route is through infection. Research shows that roughly half of SIDS victims had symptoms of a slight infection in the days before death. If breastfeeding is protective against SIDS, it may be because it protects against infection. Still, doctors agree that by far the best protection against SIDS is putting a baby to sleep on her back, eliminating bumpers, blankets, and pillows from her crib, avoiding co-sleeping, and avoiding smoking during pregnancy. If those risks were eliminated, experts calculate that the incidence of SIDS would drop from 1 in 2,000 babies to 1 in 10,000.
There is also good evidence that breastfeeding offers little or no protection against obesity,cardiovascular disease, childhood behaviours such as ADHD, asthma and allergies, type 1 diabetes, high blood pressure, dental cavities, or the following types of cancer: acute non-lymphomoblastic leukemia, non-Hodgkins lymphoma, central nervous system cancers, malignant germ cell tumors, juvenile bone tumors, and other solid cancers.
Evidence of a correlation between breastfeeding and other health outcomes is weak or mixed. The authors of one highly regarded meta analysis concluded that more research is needed to determine whether breastfeeding has an independent effect on type 2 diabetes. There are few high quality studies of breastfeeding and childhood leukemia, and those studies disagree. Most studies of an association between breastfeeding and celiac and Crohn's disease have failed to achieve statistically significant results, or found no association.
Breastfeeding may have a small impact on eczema early on, but the effect disappears in early childhood. Only one study has identified a link between breastfeeding and Hodgkins disease and neuroblastoma, but the correlation they found was very small, and the authors cautioned it might not be causal. Recent research into the effect of breastfeeding on cognitive development has offered contradictory evidence. One Brazilian study that garnered a lot of attention in the U.S. reported that breastfeeding increased not only IQ but income, while a study that compared outcomes between siblings who were formula and breastfed found no correlation. One important meta analysis concluded point blank that there is "no relationship between breastfeeding and cognitive performance."
Some public health officials take the position that even if the benefits of breastfeeding are small, we should try to achieve them. Some parents will, perfectly reasonably, agree with them. But by exaggerating the benefits of breastfeeding, we make it all too easy to cross the line from making a personal decision to breastfeed to the fervent belief that all mothers should breastfeed.
If breastfeeding really will protect a baby from everything from diabetes to cancer, it's hard to avoid the conclusion that feeding a baby formula represents some kind of parental failure. But if breastfeeding offers some modest protection against infection, it seems reasonable to allow mothers to weigh those benefits against other factors, including whether the baby is gaining enough weight and whether the mother has to return to work, to reach their own decision about what works best for their family. There are literally thousands of other things parents can, and will, do to nurture and protect their children. In the scheme of things, breastfeeding is a very small piece of the parenting puzzle.
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