The vitamin D miracle: Is it for real?

Vitamin D isn’t exactly a vitamin. Instead, it is a hormone made by a rather unusual gland: your skin. Sunlight striking the skin turns a cousin of cholesterol into pre-vitamin D. This is first processed by the liver and then activated by the kidneys or by cells in the heart, immune system, breast, or prostate. Although calcium usually gets all the credit for building bones and preventing fractures, vitamin D should get equal billing. It helps on several levels. Vitamin D ensures that calcium and phosphorus (another integral part of the bone) are absorbed as they pass through the digestive system. It signals the kidneys to hang on to these minerals so they aren’t lost in the urine. It also inhibits the breakdown of bone and boosts bone-building activity. Many studies showed that many women who break a hip have an unsuspected vitamin D deficiency. A growing body of research suggests that many Americans could reduce bone loss by getting extra vitamin D. In fact, doing this more effectively reduces hip and wrist fractures in older women and men than does dramatically increasing calcium consumption. There are other reasons to get more vitamin D besides strong bones. Here are a few of them: fewer falls, probably less cancer, as well as the possibilities of better blood pressure, a stronger heart, fewer serious infections, reduced likelihood of asthma, and protection against multiple sclerosis.

Recommended intake: The current recommended dietary allowance for vitamin D for men is 600 IU a day (15 micrograms) after age nineteen. It’s the same for women, except they should get 800 IU a day (20 micrograms) after age seventy. The optimal intake of vitamin D remains a topic of debate. I believe that the evidence shows that most people need to get at least 800 to 1,000 IU a day of vitamin D, and possibly 2,000 to 3,000 IU to get the full benefits of this vitamin. People who have darker skin or spend little time in the sun may need even more. In a 2014 study among African Americans living in Boston, increasing the daily intake to 4,000 IU offered metabolic benefits, although it did not examine actual disease risks. Ongoing research will, I trust, give more precise guidance about the best daily dose of vitamin D. You don’t need regular blood tests for vitamin D because the level varies over time and we just don’t know the right target. Instead, it’s best to take a vitamin D supplement to make sure you have enough onboard.

The current recommended dietary allowance for vitamin D for men is 600 IU a day (15 micrograms) after age nineteen. It’s the same for women, except they should get 800 IU a day (20 micrograms) after age seventy.

Recommended intake

Good food sources

Very few foods naturally contain vitamin D. Cold-water fish such as mackerel, salmon, sardines, and bluefish contain good doses of this fat-soluble vitamin; their livers contain very high levels. Most of what we get from food comes from dairy products (which by law must be fortified with vitamin D); vitamin-fortified breakfast cereals; and eggs from hens that are fed vitamin D.