With claims about the health benefits of vitamin D on the Internet, on medical TV talk shows, and in almost daily news releases, you may wonder how much vitamin D you need and how best to meet your needs for this vitamin. You may be surprised to learn that cow’s milk is the number one source of vitamin D in the American diet. Nearly all commercial brands of cow’s milk are fortified with vitamin D, and many vitamin D-fortified yogurts and some vitamin D-fortified cheeses are appearing in grocery stores to help people meet their vitamin D needs.

Vitamin D’s Role in Health

The importance of vitamin D in supporting bone health is well established by scientific evidence. Vitamin D helps maintain normal blood levels of calcium and phosphorus by enhancing their absorption. This, in turn, promotes bone growth and maintenance.

Classic vitamin D deficiency diseases include rickets in young children and osteomalacia in adults. Rickets is characterized by stunted growth, bowed legs, and delays in motor development. Recently, a physician at the University of Tennessee’s Health Science Center in Memphis suggested that Tiny Tim, one of the most enduring characters in Charles Dickens’ 1843 novel, “A Christmas Carol,” likely suffered from rickets. This disease was essentially eliminated in the U.S. decades ago following the fortification of fluid milk with vitamin D in the early 1930s. Although rare, rickets in young children has made an unexpected comeback in the U.S. in recent years, especially among African Americans. Osteomalacia is a painful condition in adults characterized by the softening, weakening, and demineralization of bones. Long-term vitamin D (and calcium) deficiency can lead to osteoporosis and increased susceptibility to fractures.

Vitamin D Status

Heightened interest in vitamin D also stems from reports of widespread vitamin D deficiency. The 2010 Dietary Guidelines for Americans calls vitamin D “a nutrient of public health concern” for children and adults, citing low dietary intake. In particular, individuals who are older and living in institutions or who have dark skin pigmentation may be at increased risk for vitamin D deficiency. According to a recent report from the Centers for Disease Control and Prevention (CDC), vitamin D deficiency is much higher among non-Hispanic African Americans than Mexican Americans or non-Hispanic whites.

Sources of Vitamin D

We obtain vitamin D from two sources: sunlight and diet. Vitamin D is called the “sunshine vitamin” because it can be synthesized in the skin when exposed to ultraviolet light from the sun. About 5 to 15 minutes of sun two or three times a week on our face, hands, and arms – without sunscreen – is considered to be sufficient to meet our vitamin D needs. However, some people may not get enough sun exposure to meet daily vitamin D recommendations. The amount of vitamin D synthesized in the skin varies widely and depends on many factors that can decrease vitamin D synthesis in the skin:

• Aging
• Increased skin pigmentation
• Use of sunscreens
• Clothing
• Winter season
• Living in northern latitudes
• Cloud cover
• Smog

Researchers speculate that lack of exposure to sun and the resulting vitamin D deficiency may have contributed to the untimely death in 1791 of the Austrian music composer, Wolfgang Amadeus Mozart, at the age of 35.

When sun exposure is limited, consuming foods and beverages providing vitamin D becomes increasingly important to meet vitamin D needs. Only a few foods naturally contain vitamin D:

• Oily marine fish (e.g., mackerel, salmon, herring)
• Cod liver oil
• Egg yolks
• Sun-exposed mushrooms

For this reason, some foods are fortified with vitamin D, beginning with fluid milk in 1932. In the U.S., fluid milk and other dairy foods such as yogurts and some cheeses, as well as some breakfast cereals, breads, and juices are fortified with this sunshine vitamin. Nearly all cow’s milk sold in the U.S. is fortified with vitamin D to obtain a standardized amount . To ensure that the level of vitamin D fortification of milk meets specifications, milk is routinely tested for its vitamin D content. Milk monitoring is conducted primarily by state governments in cooperation with the U.S. Food and Drug Administration.

When a food is fortified with vitamin D in the U.S., vitamin D must be listed on the Nutrition Facts panel as a percentage of the Daily Value (DV) . Since the American Medical Association, Council on Food and Nutrition endorsed vitamin D fortification of milk in 1933, other health professional organizations, such as the American Academy of Pediatrics, have supported vitamin D fortification of fluid milk as an important public health measure to reduce the risk of vitamin D deficiency .

Foods naturally or fortified with vitamin D are the preferred source of this nutrient, according to health professionals. One reason why foods trump supplements is that foods such as cow’s milk contain other essential nutrients important for health. Take bone health for example. In addition to vitamin D, several other nutrients in fluid milk including calcium, magnesium, phosphorus, potassium, and protein work together to support bone health.

Bottom Line

All children, adults, and the elderly are encouraged to consume nutrient-rich foods naturally containing or fortified with vitamin D. Fluid milk is the number one source of vitamin D in the diets of Americans, according to the National Health and Nutrition Examination Survey (NHANES), 2003-2006. Consuming recommended daily servings of low-fat or fat-free milk – 3 cups for those 9 years and older – and other milk products fortified with vitamin D (e.g., some yogurts and cheeses) as part of a healthful diet can help meet vitamin D recommendations.