If a pregnant woman does not have enough folic acid (also known as vitamin B9) in her body at the very beginning of her pregnancy, then her fetus may suffer these neural tube defects. That’s why doctors give folic acid to women who plan to become pregnant.

Image Nicholas D. Kristof Credit... Fred R. Conrad/The New York Times

Equally important is another micronutrient, iodine. The worst consequence of iodine deficiency isn’t goiters, but malformation of fetuses’ brains, so they have 10 to 15 points permanently shaved off their I.Q.’s.

Then there’s zinc, which reduces child deaths from diarrhea and infections. There’s iron, lack of which causes widespread anemia. And there’s vitamin A: some 670,000 children die each year because they don’t get enough vitamin A, and lack of the vitamin remains the world’s leading cause of childhood blindness.

“In the early stages of life, the die is cast,” said David Dodson, the founder of Project Healthy Children, an aid group that fights micronutrient deficiencies in Honduras and other poor countries. “If a child is not getting the right micronutrients, the effect is permanent.”

Nine years ago, Mr. Dodson was simply an American businessman running a 300-employee waste company that he had founded. Then he happened to visit Honduras and, in a hospital, encountered a mother whose newborn baby had a hole in the skull. He learned that negligible amounts of folic acid would prevent such heartbreaking defects  and his life was transformed.

“I had never seen anything in my life that could have so much impact for so little money and be sustainable,” Mr. Dodson said. He and his wife, Stephanie, sold their company and used some of the proceeds to start Project Healthy Children.

The most cost-effective way to distribute micronutrients isn’t to hand them out. Mary Flores, a former Honduran first lady who is active in nutrition, notes that impoverished women can be hard to reach, and even if they are given folic acid pills they sometimes won’t take them for fear that they actually are birth control pills. So micronutrients instead are often added to such common foods as salt, sugar, flour or cooking oil.