This week's expert: Dr. Lance Luria is 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, cancer and 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 jump-start from sunshine. The problem is that most of us aren't getting enough ultra-violet (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, which includes Springfield, 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 depots act as a sort of sinkhole for vitamin D.
Q. How much vitamin D is needed?
A. Current recommendations call for 200 international units (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.
Q. Why is vitamin D needed?
A. Maintaining adequate blood levels of vitamin D is important not only for bone health but also in the prevention of a number of chronic diseases, including osteoporosis, hypertension and prostate, breast and colon cancers.
Q. Are there food sources of vitamin D?
A. Naturally occurring vitamin D is relatively rare in foods. Oily fish and egg yolks contain significant amounts, as do mushrooms.
Q. What's the difference between vitamin D2 and D3?
A. Supplemental vitamin D comes in two forms: D2 (ergocalciferol) or D3 (cholecalciferol). Vitamin D2 comes from UVB-irradiated yeast and plants; vitamin D3 comes from UVB-irradiated lanolin from animal sources.
It was originally thought that vitamins D2 and D3 were pretty much the same, but now we know that the D2 form is only about 20 percent to 40 percent as effective as D3. Vitamin D2 also doesn't last as long in our circulation and may even cause premature breakdown of circulating D3.
Fortified foods can contain either vitamin D2 or D3, but recent studies in the United States and western Canada noted that up to 80 percent of milk did not contain the advertised amount of vitamin D and half the milk tested contained less than 50 percent of the advertised amount. Remarkably, 15 percent of the skim milk samples contained no detectable vitamin D at all.
Q. How common is vitamin D deficiency?
A. It is estimated that 1 billion people worldwide don't get enough vitamin D. That includes vitamin D deficiency among 40 percent to 100 percent of independently living elderly Americans and Europeans. Further, in the United States, half of women receiving treatment for osteoporosis, 73 percent of pregnant women (and 80 percent of their infants at birth) and between 48 and 52 percent of adolescent girls in the Northeast show vitamin D deficiency.
This is a problem because without vitamin D, only 10 percent to 15 percent of dietary calcium is absorbed, and bone mineral density is directly correlated with vitamin D levels.
Q. How can you get enough vitamin D?
A. If you believe you need to increase your vitamin D levels, here are some tips:
- During the spring, summer and fall, 5 to 15 minutes of sunshine between 10 a.m. and 3 p.m., two or three times weekly, should do the trick. (But, if your skin becomes slightly pink, you've gotten too much sun. )
- Tanning beds, when used in moderation, provide ample vitamin D and may be particularly helpful in the winter months.
- Milk, cereals and bread products that contain vitamin D may be highly variable in their vitamin D content and should not be depended upon as a reliable source.
- Don't forget that vitamin D2 (from yeast and plants) is probably only one-third as effective as vitamin D3 (from animals). So when you go shopping for supplements, remember that 1,000 IU of D3 is comparable to 3,000 IU of D2.
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