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Vitamin D

What are the sources of vitamin D?

Food Sources

Fortified foods are common sources of vitamin D [4]. In the 1930s, rickets was a major public health problem in the United States (U.S.). A milk fortification program was implemented to combat rickets, and it nearly eliminated this disorder in the U.S. [4,9]. About 98% to 99% of the milk supply in the U.S. is fortified with 10 micrograms (ìg) (equal to 400 International Units or IU) of vitamin D per quart. One cup of vitamin D fortified milk supplies one-half of the recommended daily intake for adults between the ages of 19 and 50, one-fourth of the recommended daily intake for adults between the ages of 51 and 70, and approximately 15% of the recommended daily intake for adults age 71 and over.

Although milk is fortified with vitamin D, dairy products made from milk, such as cheese and ice creams, are generally not fortified with vitamin D and contain only small amounts. Some ready-to-eat breakfast cereals may be fortified with vitamin D, often at a level of 10% to 15% of the Daily Value*. There are only a few commonly consumed foods that are good sources of vitamin D [4]. Suggested dietary sources of vitamin D are listed in Table 1.

*DV = Daily Value. DVs are reference numbers developed by the Food and Drug Administration (FDA) to help consumers determine if a food contains a lot or a little of a specific nutrient. The DV for vitamin D is 400 IU (10 μg) for adults. Most food labels do not list vitamin D content unless a food has been fortified with this nutrient. The percent DV (%DV) listed on the table above tells you the percent of the DV provided in one serving. A food providing 5% of the DV or less is a low source while a food that provides 10-19% of the DV is a good source and a food that provides 20% or more of the DV is high in that nutrient. It is important to remember that foods that provide lower percentages of the DV also contribute to a healthful diet. For foods not listed in this table, please refer to the U.S. Department of Agriculture’s Nutrient Database Web site: http://www.nal.usda.gov/fnic/cgi-bin/nut_search.pl.

Sun exposure
Sun exposure is perhaps the most important source of vitamin D because exposure to sunlight provides most humans with their vitamin D requirement [13]. UV rays from the sun trigger vitamin D synthesis in skin [13-14]. Season, geographic latitude, time of day, cloud cover, smog, and sunscreen affect UV ray exposure and vitamin D synthesis [14]. For example, sunlight exposure from November through February in Boston is insufficient to produce significant vitamin D synthesis in the skin. Complete cloud cover halves the energy of UV rays, and shade reduces it by 60%. Industrial pollution, which increases shade, also decreases sun exposure and may contribute to the development of rickets in individuals with insufficient dietary intake of vitamin D [15]. Sunscreens with a sun protection factor (SPF) of 8 or greater will block UV rays that produce vitamin D, but it is still important to routinely use sunscreen to help prevent skin cancer and other negative consequences of excessive sun exposure. An initial exposure to sunlight (10 -15 minutes) allows adequate time for Vitamin D synthesis and should be followed by application of a sunscreen with an SPF of at least 15 to protect the skin. Ten to fifteen minutes of sun exposure at least two times per week to the face, arms, hands, or back without sunscreen is usually sufficient to provide adequate vitamin D [14]. It is very important for individuals with limited sun exposure to include good sources of vitamin D in their diet.

What is vitamin D?

What are the sources of vitamin D?

What is the recommended intake for vitamin D?

When can vitamin D deficiency occur?

What are some current issues and controversies about vitamin D?