WHAT IT IS: A steroid vitamin, vitamin D is a group of fat-soluble pro-hormones that is important for absorbing and metabolizing calcium and phosphorus. Actually “vitamins” cannot be synthesized by the body—they are only available through diet. Vitamin D, for this reason, is not a true vitamin: Given adequate sunlight, the body will synthesize enough. Americans are very low in vitamin D: the recent NHANES studies show that 70 percent of children across the US were insufficient, with blood concentrations of 30 ng/ml or less. Thirty to 50 is considered a good range.
[ Benefits ]
Adequate vitamin D levels help protect genes in healthy people, shielding them from cancer as well as autoimmune, cardiovascular, and infectious diseases. It helps the brain work well later in life, can reduce asthma symptoms, helps with weight loss and with maintaining a healthy weight, and reduces women’s risk of developing rheumatoid arthritis. It is also necessary for the body to absorb calcium, thus preventing osteoporosis among seniors.
[ Sources ]
Half an hour outdoors when the UV rating is three or over can net you 10,000 IUs. Not many foods have substantial levels, though fish like salmon and mackerel have some, as do beef liver, cheese, and egg yolks. Fortified foods typically have 100 IU or less per serving, so it is best to get your vitamin D through sunlight or supplements.
Few foods naturally contain vitamin D. The flesh of fatty fish (such as trout, salmon, tuna, and mackerel) and fish liver oils are among the best sources. An animal’s diet affects the amount of vitamin D in its tissues. Beef liver, egg yolks, and cheese have small amounts of vitamin D, primarily in the form of vitamin D3. Mushrooms provide variable amounts of vitamin D2. Some mushrooms available on the market have been treated with UV light to increase their levels of vitamin D2. In addition, the Food and Drug Administration (FDA) has approved UV-treated mushroom powder as a food additive for use as a source of vitamin D2 in food products
[ Warnings ]
For vitamin D to be properly utilized you also need cofactors magnesium, zinc, and boron, as well as vitamins A and K2. Toxicity from this vitamin is a rare but serious disease caused by “megadoses” of supplements over several months resulting in blood levels over 150 ng/ml.
[ Recommended Dosage ]
The National Institutes of Health recommends 400 IU per day for infants, 600 IUs per day for those one to 70, and 800 IUs for those over 70. For those who are deficient, however, higher doses are required. Mark Hyman, MD, says the optimal level is 45 ng/ml and that requires 3,000 – 4,000 IUs per day. If we could achieve that level, he says, we’d have 400,000 fewer premature deaths a year.
Sensible sun exposure on bare skin for 5–10 minutes, 2–3 times per week, allows most people to produce sufficient vitamin D. However, it breaks down quite quickly, meaning that stores can run low, especially in winter. People who live in northern latitudes or areas of high pollution, work night shifts, or are homebound should aim to consume vitamin D from food sources whenever possible.