Every year some 3 million children around the world die of diarrhea. Even those who survive may be handicapped by reduced intelligence. Richard Guerrant, a physician at the University of Virginia, studied 26 children from a poor community in Fortaleza, Brazil. Those who endured the most diarrhea in their first two years of life were most likely to score poorly on cognitive tests given between ages 6 and 9. Guerrant speculates that diarrhea-inducing bacteria, viruses, and parasites impair the absorption of nutrients vital for brain development.