D Is for Defense: Why Vitamin D Is the Ultimate Super Vitamin

How Vitamin D Works

To bone up on D, it helps to know how the vitamin works. We get small amounts of it from food, especially fortified dairy products, but the nutrient is mainly produced from ultraviolet B radiation in sunshine. Those rays penetrate our skin and transform cholesterol-like molecules there into a preliminary form of D that circulates in the blood. It then travels to receptors in the liver and the kidney, where it becomes mobilized to do its number-one job of regulating calcium and storing it in our bones. "Once that's done, D begins to have other benefits," Dr. Holick says. For one thing, it triggers the genes in our bodies that inhibit cell growth, which may prevent cancer cells from forming. In fact, women who spend more time outdoors in the sun and drink 10 or more glasses of milk a week when they're in their teens and 20s have lower rates of breast cancer than women who don't, according to one recent study. Other research suggests that getting too little D can increase the risk of colon, ovarian, and breast cancers. The vitamin also regulates the activity of the immune system's cells, helping to ward off infections and protect against such auto-immune diseases as lupus, multiple sclerosis, and rheumatoid arthritis.

And that's not all. D helps prevent inflammation in the body, which has been linked to heart disease, and it regulates blood pressure. Azzie Young, PhD, president and CEO of Mattapan Community Health Center in Boston, discovered this for herself three years ago. Young started taking megadoses of the vitamin once a week for two months as prescribed by her doctor after she was diagnosed with vitamin D deficiency. As a result, her blood pressure dropped, and she now sleeps better, is more energized, and has fewer aches and pains. "I was blown away that something so simple, safe, and inexpensive could make that big a difference," Young says. She has since started a vitamin D-awareness initiative to help spread the word about this powerful pill.