HEALTH: The breastfeeding story is more complicated than you think, by Carolyn Johnson.

The popular notion of breast milk as a panacea has stemmed from dozens of studies that have reported benefits ranging from a lower risk of asthma to increased IQ. But flaws in some of the studies tracking long-term health effects raise questions about the magnitude — and at times the existence — of some of those advantages. Many fail to properly control for factors such as the mothers’ education and wealth. When those effects are accounted for, the benefits almost always shrink.

In other words, some of the advantage that studies ascribe to mothers’ milk can be explained by infants’ environments and parents, particularly in high income countries.