The following is from an interview on News-leader.com, which features a discussion of vitamin D with Lance Luria, an internal medicine physician and the associate medical director of St. John's Health Plans.
Q. Over the past few years, vitamin D has been making headlines. Why is that?
A. Vitamin D was discovered in the early part of the 20th century when it was found that adding a fat-soluble factor "D" to the diet prevented rickets, a disease that results in defective bone growth and bowed legs. More recently, numerous large studies have raised questions as to whether the standard recommendations assure optimal vitamin D levels. These questions come on the heels of mounting evidence pointing to the important role vitamin D plays in promoting bone health, in addition to preventing osteoarthritis, diabetes and cancer, as well as mental, cardiovascular and neuromuscular diseases.
Q. Where does vitamin D come from?
A. Since our bodies have the ability to make vitamin D, it is not technically a vitamin, but falls more in the category of a steroid-like hormone that just needs a jumpstart from sunshine. The problem is that most of us aren't getting enough UVB rays to generate sufficient vitamin D. Here are some interesting points:
- During the summer, 10 minutes of exposure of your hands and face (without sunscreen) provides about 400 international units (IU) of vitamin D3. A young person whose entire body is exposed to simulated sunlight produces the equivalent of 10,000-25,000 IU of vitamin D taken orally.
- Don't worry about getting too much vitamin D from sunlight. The same UVB rays that help make vitamin D will also destroy what is not absorbed quickly enough.
- Wearing sunscreen blocks your body's ability to make vitamin D.
- People living north of the 37th degree-latitude line don't get enough UVB rays in winter. A good rule of thumb is that you don't get enough during the seasons when your shadow at noon is taller than you are.
- Your ability to make vitamin D decreases as you reach old age.
- Darker-pigmented people have more melanin in their skin, and since melanin acts like sunblock, less vitamin D is made. In fact, a black person with very dark skin pigmentation will require about a tenfold longer exposure to make the same amount of vitamin D as a light-skinned white person.
- Vitamin D is stored in fat cells, which can act as a reservoir for the winter months. Paradoxically, obese people have about one-half the levels of circulating vitamin D levels as people of normal weight. It is thought that large fat deposits act as a sort of sinkhole for vitamin D.
Q. How much vitamin D is needed?
A. Current recommendations call for 200 IU for children and adults up to age 50, 400 IU from age 51 to 70 and 600 IU for adults 71 and older. However, based on more recent studies, most authorities are now recommending at least 800 IU of vitamin D3 daily for children and adults if you're not getting enough UVB exposure and at least 1,000 IU daily for those that do not get any UVB exposure. A safe upper limit is 2,000 IU daily. Although a number of studies have shown that higher daily intakes do not result in toxic effects, these higher doses are not routinely recommended. If you're not sure that your intake is adequate, taking a daily supplement of 1,000 IU of vitamin D3 is currently recommended by a number of authorities. Tests to show vitamin D blood levels are available but costly, but they can resolve those situations where there remains a question as to whether you are getting enough.
