For healthy people between 1 and 70 years of age, the recommended daily allowance (RDA) for vitamin D is 600 IUs, states the National Institutes of Health's Office of Dietary Supplements. For people over the age of 70, the recommended daily intake is 800 IUs, and infants between 0 to 12 months need 400 IUs.
Vitamin D is an important vitamin for the body because it helps with the absorption of calcium that is necessary to maintain healthy bones. Moreover, vitamin D is needed for the immune system. Insufficient amounts of vitamin D can lead to diseases such as rickets and osteomalacia, notes NIH's Office of Dietary Supplements.
Foods such as milk and eggs are good sources of vitamin D. Some foods are also fortified with vitamin D. Another source of vitamin D is through skin exposure to sunlight, states Cleveland Clinic. Supplementation is another way to get enough vitamin D to keep the body working at an optimum level.