There are many studies in pediatric literature—some going back more than 80 years—that support the notion that children with iron-deficiency anemia lag in cognitive development. The problem is that it is very hard to be sure that the differences in cognitive development are due to the anemia rather than other factors like poverty, concurrent illness, and parents less likely to know or follow the principles of good nutrition. Studies of this kind are extremely hard to keep in control since we can't ethically begin a study by randomly assigning one group of children to a state of deprivation. Looked at critically, most of the anemia studies don't stand up. Sally Grantham-McGregor and Cornelius Ani of University College, London, examined these questions in a review a few years ago.

But the stakes are high here: If iron deficiency in early life leads to deficiencies in cognitive development, it looks as if the effect will be long-standing and probably permanent. So, even though the evidence is still uncertain, it seems prudent to do what we can to decrease the risk of iron deficiency.