Although children who are breastfed have better neurodevelopmental outcomes, whether this is a biological or nutritional effect, an environmental effect, a genetic effect, or some combination of these factors is unclear. Because a randomized trial comparing breastmilk with formula is impossible, investigators must rely on observational studies, which creates methodologic difficulties. Potential confounding variables must be identified and addressed. Women who choose to breastfeed tend to have attributes, such as a higher level of education, that are associated with better developmental outcome<sup>12 De Andraca I., Uauy R. Breastfeeding for optimal mental development. The Alpha and the Omega in human milk World Rev Nutr Diet 1995 ;  78 : 1-27

Cliccare qui per andare alla sezione Riferimenti</sup>; however, evidence also supports a biological or nutritional role. Docosahexaenoic acid (DHA), a long-chain polyunsaturated fatty acid present in large quantities in the brain and retina, is present in human milk but not in commercial formula. The role of human milk in neurodevelopmental outcome, with emphasis on visual and cognitive outcome in term and preterm infants, is reviewed.