Vitamin D
Vitamin D is a fat-soluble vitamin that the human body uses to maintain normal calcium metabolism and promote bone health. The body can synthesize vitamin D when the skin is exposed to ultraviolet radiation from the sun. Vitamin D can also be obtained from both natural food sources and fortified foods. Vitamin D deficiency can create many health problems, and severe vitamin D deficiency results in a condition known as rickets, a debilitating decalcification of the bones. Rickets was common among American children until the 1940s, when the U.S. government began a widespread program to fortify milk with vitamin D.
Today, important new studies have renewed interest in the role vitamin D plays in maintaining health and preventing disease. Scientific evidence associates vitamin D deficiency with an increased incidence of many diseases – including cancer, cardiovascular disease, osteoporosis, stroke, Parkinson’s disease and autoimmune disorders – and suggests that supplemental vitamin D can help prevent these serious health conditions.
New discoveries about vitamin D’s role in human health have been so important that Time magazine named “The Benefits of Vitamin D” as one of the top ten medical breakthroughs of 2007. Adding his perspective to the excitement, interventional nutrition expert Dr. Greg Plotnikoff doesn’t mince words: “Because vitamin D is so cheap and so clearly reduces all-cause mortality, I can say this with great certainty: Vitamin D represents the single most cost-effective medical intervention in the United States”.
Functions
Vitamin D plays a critical role in many physiological processes, including calcium balance, blood pressure regulation, insulin production, cell differentiation and immune system function. Vitamin D’s most important functions involve maintaining normal blood levels of calcium, assisting calcium absorption and building bone mass.
Sources
Vitamin D is available from three basic sources: sunlight, food and supplements. Most people depend on a combination of these sources to meet their needs.
Sunlight
Exposure to sunlight stimulates the epidermis of the skin to produce vitamin D. In fact, many people meet their entire vitamin D requirement by exposure to the sun. however, people with dark skin and those with limited exposure to sunlight need to be especially careful to ensure that their vitamin D needs are met through diet or supplementation.
Food Sources
While most vitamins are found abundantly in many of the foods we eat, food sources of vitamin D are quite limited. The best food sources are egg yolks and oily fish such as salmon, mackerel and sardines. Foods with small amounts of vitamin D include oatmeal, parsley, sweet potatoes and dandelion greens.
Fortified Foods
Because natural food sources of vitamin D are so limited, food manufacturers routinely fortify processed foods with vitamin D. The U.S. government initiated fortification in response to the high incidence of rickets among children in the first half of the twentieth century. In fact, in the 1920s, 75 percent of children in New York Public Schools had some form of rickets. In the 1940s, U.S. dairies began fortifying milk with vitamin D, which led to drastic reductions in the incidence of rickets in the U.S. population.
Today, the foods most commonly fortified with vitamin D include milk, orange juice, yogurt and breakfast cereals. Eight ounces of milk or fortified orange juice contain 100 IU of vitamin D, and a one-cup serving of fortified breakfast cereal contains 40 to 50 IU. Not all breakfast cereals or brands of orange juice are fortified with vitamin D, so it’s important to read the labels to determine exact vitamin D content.
Dietary Supplements
Vitamin D is also available in supplement form, either as part of multivitamin formulas or as an individual supplement. Taking a vitamin D supplement is the easiest and most effective way to ensure an adequate intake of vitamin D.
