The health benefits of vitamin D have been making news for some time now, but roughly two-thirds of Americans still are not getting enough of this vital nutrient.

Even though vitamin D has long been known to promote bone strength—it enables bone-building calcium to pass through the small intestine and into the bloodstream and the bones many other health benefits are being discovered. Most recently, research findings have shown that low vitamin D also is linked to chronic diseases, such as…

  • Cancer. For example, about half of colorectal cancers in the US are believed to be preventable by raising vitamin D levels in people who are deficient.
  • Dementia. Adults age 65 and older with the lowest levels of vitamin D were found to be more than twice as likely to suffer cognitive impairment (which often precedes dementia) than those with optimal levels of the vitamin.
  • Diabetes. People who get more than 800 international units (IU) of vitamin D daily may be about one-third less likely to develop type 2 diabetes.
  • Heart disease. Risk for heart disease was reduced by 31% in women who took vitamin D supplements as part of a study on osteoporosis-related fractures.

How could one vitamin have such a profound effect on overall health? Research now shows that vitamin D helps facilitate cellular health in virtually every cell in the body including those in the brain. If this cellular health is interrupted due to a vitamin D deficiency, health problems, such as those described earlier, may occur.

Little-Known Facts

What you may not know about vitamin D…

  • Few doctors recommend a blood test to measure 25-hydroxyvitamin D, a form of vitamin D that acts as a marker for vitamin D status.
  • Adults over age 60 should ask to be tested.* They are at increased risk for vitamin D deficiency since the skin becomes less able to manufacture the vitamin from sunlight as the body ages.

Recommended blood level of vitamin D: Thirty to 100 nanograms of 25-hydroxyvitamin D per milliliter (ng/ml.) of blood. I like to keep patients between 40 ng/mL and 60 ng/ml, but up to 100 ng/mL is safe.

*Vitamin D testing is covered by most health insurers, including Medicare.

Helpful: It's best to get tested in the winter, when levels are likely to be lower than in the summer. If you are deficient, your doctor will prescribe therapeutic doses of vitamin D. Get retested eight to 12 weeks later, then follow up once a year.

  • Low energy, bone pain (especially in the arms and legs and/or lack of muscle strength can indicate a vitamin D deficiency. A condition known as osteomalacia, which causes softening of the bones, can result from vitamin D deficiency. Unlike osteoporosis, which occurs when existing bone is weakened, osteomalacia is an abnormality in the bone-building process. People with osteomalacia complain of throbbing and aching bone pain.

Simple self-test: Press firmly with your thumb or forefinger on your breastbone or your shins. If you feel pain in either of those areas, you're probably low in vitamin D and may have osteomalacia. See a doctor to have your vitamin D status tested.

  • The US recommendations for vitamin D are too low. The Office of Dietary Supplements, part of the National Institutes of Health, advises Americans to get 600 IU of vitamin D daily from food and/or supplements if you're age 50 to 70... and 800 IU daily for those over age 70.

My advice: If you don't think you can get enough timed sun exposure without sunscreen (see opposite), get 1,500 IU to 2,000 IU of vitamin D daily. Foods that contain vitamin D (such as wild-caught salmon, mushrooms and vitamin D-fortified milk and breakfast cereals) do not provide significant amounts of the vitamin. Many people will also need to take a vitamin D supplement.

Important: A supplement is especially critical if you don't get much sun due to your distance from the equator-for example, you live in Seattle rather than Miami.

Supplements also are required for people who have been tested and are low in vitamin D. and are more frequently necessary for dark-skinned people because dark skin pigmentation naturally filters vitamin D-producing sun rays.

  • The vitamin D produced from sunlight is superior to that provided by supplements. Sun-produced vitamin D has been shown to last at least twice as long in the blood as vitamin D from supplements.

There are no simple formulas to determine the amount of sun exposure needed to produce adequate amounts of vitamin D.

My general guideline: Three times a week—during the period of 10 a.m. to 3 p.m. (virtually no vitamin D is produced at other times)—spend one-quarter to one-half the amount of time in the sun that it takes you to get the beginning of a sunburn. For someone with dark skin, this might be 30 minutes three times weekly. If you're fair-skinned, five to 10 minutes might be enough. Expose your arms and legs—and, if possible, your abdomen and back-to sun. During timed exposures, put sunscreen on your face to help prevent sun damage. When you're not doing a timed exposure, cover all exposed skin with sunscreen to prevent sunburn.

Note: If you live above 330 latitude (roughly any area north of Atlanta), you cannot produce any significant vitamin D from sun exposure during the winter.

  • Inadequate sun exposure may increase your risk for melanoma and other cancers. Sunburn increases the risk for skin cancer, but there is no scientific evidence that moderate sun exposure has the same effect. In fact, most melanomas (the most lethal form of skin cancer) occur on parts of the body that receive little sun. Research published in the Journal of Investigative Dermatology shows that people who get regular, moderate sun exposure are less likely to develop melanoma than those who get little or no sun. Melanoma kills about 8,600 Americans annually. Colon, prostate and breast cancers combined claim about 115,000 lives. Each of these cancers has been linked to insufficient vitamin D.

Important finding: A study in the journal Cancer reported that insufficient sun exposure in the US accounted for 85,000 more cancer cases than would have occurred had the same people gotten more sun.

  • Certain medications reduce vitamin D levels. Antiseizure drugs, such as phenytoin (Dilantin), the steroid prednisone, AIDS medications and some other drugs destroy vitamin D and increase one's risk for osteomalacia and other conditions associated with vitamin D deficiency.

**If you take a prescription drug or are at high risk for skin cancer or have a history of the disease, consult your doctor

People taking such drugs may need double or triple the usual amounts of vitamin D. Other medications that reduce vitamin D include the cholesterol-lowering drug cholestyramine (Questran)...the weight-loss medication orlistat (Xenical)...and the herb Saint John's wort.

If you take one of these products, you may need to take a vitamin D supplement to maintain adequate blood levels of the vitamin.

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