The United States Food and Drug Administration’s Recommended Dietary Allowance (RDA) of vitamin D is 10 micrograms for men, women, and children. Most people are able to easily obtain such a dosage through regular exposure to sunlight, which reacts with the vitamin D precursor, 7-dehydrocholesterol, present in the skin to produce adequate levels of the vitamin. In some northern locations during winter or areas suffering from severe air pollution, however, individuals may not come into contact with enough ultraviolet rays to produce sufficient quantities of vitamin D. In such cases, bodily vitamin D levels can be supplemented through the diet by consuming items such as liver, fish oils, and fortified milk.