A steroid vitamin which promotes the intestinal absorption and metabolism of calcium and phosphorus. Under normal conditions of sunlight exposure, no dietary supplementation is necessary because sunlight promotes adequate vitamin D synthesis in the skin. Deficiency can lead to bone deformity (rickets) in children and bone weakness (osteomalacia) in adults.
Vitamin D comes from the diet (eggs, fish, and dairy products) and is produced in the skin. Skin production of the active form of vitamin D depends 0n exposure to sunlight. Active people living in sunny regions produce most of the vitamin D they need from their skin. In less sunny climes the skin production of vitamin D is markedly diminished in the winter months, especially among the elderly and the housebound. In that population, vitamin D supplements become important.
Vitamin D deficiency among the elderly is quite common in the US. In a study of hospitalized patients in a general medical ward, vitamin D deficiency was detected in 57% of the patients. An estimated 50% of elderly women consume far less vitamin D in their diet than recommended.
The Food and Nutrition Board of the Institute of Medicine has recommended the following as an adequate vitamin D intake: 200 IU daily for people 19-50 years old; 400 International Units (IU) daily for those 51-70 years old; and 600 IU daily for those 71 years and older. An average multivitamin tablet contains 400 IU of vitamin D. Therefore, taking a multivitamin a day should help provide the recommended amount of vitamin D.
As to children, the National Academy of Sciences and American Academy of Pediatrics have recommended that all infants, including those who are exclusively breastfed, have a minimum intake of 200 International Units (IU) of vitamin D per day beginning during the first 2 months of life. In addition, it is recommended that an intake of 200 IU of vitamin D per day be continued throughout childhood and adolescence, because adequate sunlight exposure is not easily determined for a given individual.