I read this Economist article about nutrition in the developing world that shed some light.  Here are some great passages:

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More than 160m children in developing countries suffer from a lack of vitamin A; 1m die because they have weak immune systems and 500,000 go blind each year. Iron deficiency causes anaemia, which affects almost half of poor-country children and over 500m women, killing more than 60,000 of them each year in pregnancy. Iodine deficiency—easily cured by adding the stuff to salt—causes 18m babies each year to be born with mental impairments.

…And nutrition can also be improved in all sorts of ways, including by better sanitation, which reduces intestinal diseases and enables people to absorb more nutrients; by investing in smallholder farming, to increase dietary variety; by vaccinating children against diseases; by educating women to breastfeed babies for longer, to improve immunity. Marie Ruel, of the International Food Policy Research Institute in Washington, DC, ticks off some of the tasks: focus on the first 1,000 days of life (including pregnancy); scale up maternal-health programmes and the teaching of good feeding practices; concentrate on the poor; measure and monitor the problem.