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 vitamin D insufficient, with blood concentrations of 30 ng/ml or less. Thirty to 50 is considered a good range.
dequate vitamin D levels help protect genes in healthy people, shielding them from cancer as well as autoimmune, cardiovascular, and infectious diseases. Vitamin D 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.
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.
For vitamin D to be properly utilized you also need cofactors magnesium, zinc, and boron, as well as vitamins A and K2. Vitamin D toxicity is a rare but serious disease caused by “megadoses” of supplements over several months resulting in blood levels over 150 ng/ml.
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 vitamin D 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.