Vitamin D is a main component in helping to prevent rickets. Rickets is a bone-softening illness that interferes with normal ossification. A child with a vitamin D deficiency is much more susceptible to this disease, which can cause bowed legs and other bone deformities. The AAP has found that 400 IU a day can help to prevent and treat rickets. In addition, adequate vitamin D throughout childhood can help reduce the risk of osteoporosis. Evidence also shows vitamin D plays a role in the immune system, and may help prevent infections, cancer, and diabetes in adults.
Vitamin D can be found in some foods and is also synthesized by exposure to sunlight. Children can get an adequate amount of the nutrient by drinking six glasses of milk a day or eating fatty fish such as salmon or mackerel. (High mercury levels in certain kinds of fish, including mackerel, can be harmful to a child's health and should be limited. For a full list of fish and their mercury levels, print off our seafood safety guide.) However, because children's diets are unlikely to meet these standards, and prolonged exposure to sunlight is not recommended, a supplement may be needed.