Over two billion people worldwide are at risk for not getting enough vitamin A, iodine, and/or iron, especially in Southeast Asia and sub-Saharan Africa. Pregnant women and young children are most vulnerable. Other important nutrient deficiencies include zinc, folate, and B vitamins, but there isn't much data on how common they are. In many places, people lack more than one essential nutrient, so it's important to find simple ways to address multiple nutrient deficiencies.