D Vitamin Facts

Vitamin D, calciferol, is a fat-soluble vitamin. It is found in food, but also can be made in your body after exposure to ultraviolet rays from the sun ^1,2. Vitamin D exists in several forms, each with a different activity. Some forms are relatively inactive in the body, and have limited ability to function as a vitamin. The liver and kidney help convert vitamin D to its active hormone form.³

The major biologic function of vitamin D is to maintain normal blood levels of calcium and phosphorus ⁴. Vitamin D aids in the absorption of calcium, helping to form and maintain strong bones. It promotes bone mineralization in concert with a number of other vitamins, minerals, and hormones. Without vitamin D, bones can become thin, brittle, soft, or misshapen.

Vitamin D prevents rickets in children and osteomalacia in adults, which are skeletal diseases that result in defects that weaken bones.^5,6

What are the sources of vitamin D?

Food sources

Fortified foods are the major dietary sources of vitamin D.⁴ Prior to the fortification of milk products in the 1930s, rickets (a bone disease seen in children) was a major public health problem in the United States. Milk in the United States is fortified with 10 micrograms (400 IU) of vitamin D per quart , and rickets is now uncommon in the US.⁷

One cup of vitamin D fortified milk supplies about one-fourth of the estimated daily need for this vitamin for adults. Although milk is fortified with vitamin D, dairy products made from milk such as cheese, yogurt, and ice cream are generally not fortified with vitamin D. Only a few foods naturally contain significant amounts of vitamin D, including fatty fish and fish oils ⁴. The table of selected food sources of vitamin D suggests dietary sources of vitamin D.

Exposure to sunlight

Exposure to sunlight is an important source of vitamin D. Ultraviolet (UV) rays from sunlight trigger vitamin D synthesis in the skin.^7,8 Season, latitude, time of day, cloud cover, smog, and suncreens affect UV ray exposure.⁸ For example, in Boston the average amount of sunlight is insufficient to produce significant vitamin D synthesis in the skin from November through February. Sunscreens with a sun protection factor of 8 or greater will block UV rays that produce vitamin D, but it is still important to routinely use sunscreen whenever sun exposure is longer than 10 to 15 minutes. It is especially important for individuals with limited sun exposure to include good sources of vitamin D in their diet.

As the 2000 Dietary Guidelines for Americans state, “Different foods contain different nutrients. No single food can supply all the nutrients in the amounts you need.”³⁵ The following table suggests dietary sources of vitamin D. As the table indicates, fortified foods are a major source of vitamin D. Breakfast cereals, pastries, breads, crackers, cereal grain bars and other foods may be fortified with 10% to 15% of the DV for vitamin D. It is important to read the nutrition facts panel of the food label to determine whether a food provides vitamin D.

Selected Food Sources of Vitamin D
Food, (International Units), [%DV*]

• Cod Liver Oil, 1 Tbs. (1,360 IU) [340]
• Salmon, cooked, 31/2 oz (360 IU) [90]
• Mackerel, cooked, 3 1/2 oz (345 IU) [90]
• Sardines, canned in oil, drained,3 1/2 oz (270 IU) [70]
• Eel, cooked, 3 1/2 oz (200 IU) [50]
• Milk, nonfat, reduced fat, and whole, vitamin D fortified, 1 c (98 IU) [25]
• Margarine, fortified, 1 Tbs. (60 IU) [15]
• Cereal grain bars, fortified w/ 10% of the DV, 1 each (50 IU) [10]
• Pudding, 1/2 c prepared from mix and made with vitamin D fortified milk (50 IU) [10]
• Dry cereal, Vit D fortified w/10%* of DV, 3/4 c (40-50 IU) [10]
  * Other cereals may be fortified with more or less vitamin D
• Liver, beef, cooked, 3 1/2 oz (30 IU) [8]
• Egg, 1 whole (vitamin D is present in the yolk) (25 IU) [6]

* DV = Daily Value. DVs are reference numbers based on the Recommended Dietary Allowance (RDA). They were developed to help consumers determine if a food contains very much of a specific nutrient. The DV for vitamin D is 400 IU. The percent DV (%DV) listed on the nutrition facts panel of food labels tells adults what percentage of the DV is provided by one serving. Percent DVs are based on a 2,000-calorie diet. Your Daily Values may be higher or lower depending on your calorie needs. Foods that provide lower percentages of the DV will contribute to a healthful diet.

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