Rickets, or the softening and weakening of bones in children, is usually caused by an extreme and prolonged vitamin D deficiency; children who are 3 to 36 months old are at highest risk because their bones are growing so fast. In the late 19th century, doctors realized that vitamin-D-rich cod liver oil helped to prevent and treat rickets in children; manufacturers added vitamin D to milk for the first time in the 1930s, and rickets has since become rare in the United States. When nutritional rickets is diagnosed, supplementation with calcium and vitamin D corrects most bone damage within a few months, sometimes within a few days. The American Academy of Pediatrics recommends that all infants, children, and adolescents receive a minimum daily intake of 400 IU of vitamin D.
