Iron deficiency

From Essential Iron:
"Long-Term Effects of Iron Shortage
"Iron is essential for the nerves in the brain to develop," says Steve Elliott, MD, of Pediatric Associates of Northern Kentucky. "If infants don't get enough iron at the start of life, they can have neuro-cognitive problems for the rest of their lives. These can affect motor skills, reading and math abilities. Even if iron deficiency is corrected, these children do not score as well in standardized tests later."

Some of the signs of iron deficiency that parents may notice include irritability or paleness. If the condition persists, children become anemic, a condition in which the body lacks enough red blood cells to carry the oxygen it needs for fuel.

"Children born full-term have some iron stores in their bodies, but it's vital for a child to take in additional iron through breast milk or fortified formula," Dr. Elliott says."
There is a discussion of a new paper An Empirical Analysis of the Gender Gap in Mathematics in the Marginal Revolution post The gender gap in math is weak in Muslim countries One of the comments suggest that in some cases the gender differences in math. ability may be in part due to iron deficiency: "The gender gap starts when girls hit puberty and begin to have their periods, which causes iron deficiency anemia and low iron levels in some girls, and low iron is associated with poor math ability.

So, my personal theory is that the math part of the brain is particularly sensitive to decreased oxygen levels in the blood. If women of a particular culture tend to eat more iron rich foods, or if a particular ethnicity is less susceptible to iron deficiency, then that might make a difference."
Another comment suggests cultural differences in some cases: "There is great heterogeneity among countries in the Moslem world. In the rich Gulf nations, almost every girl goes on to get a college degree, and tend to do much better in school than males because it is one of the few areas in which they are allowed to excel. Many males (possibly a majority, but it is hard to get reliable statistics) don't finish high school, because the excess oif wealth in these countries means that they'll never have to work, and will never be poor.

When I taught in the Gulf I was shocked by the quality differential between the males and females. The girls were almost all inquisitive, thoughtful and hard workers who knew how to get to the nub of an (academic) problem and ask good questions. Most of the boys basically had to be prodded with a stick to divine whether they were sentient or not."
Probably there will be many more discussions after the above paper of Fryer and Levitt.