Until recently, physicians rarely diagnosed deficiencies of vitamin D except in occasional cases of childhood rickets (a disease in which the bones do not harden).

Now: One in three Americans is considered to be deficient in vitamin D-and most of them don't know it, according to the US National Center for Health Statistics.

How did vitamin D deficiency become such a widespread problem so quickly—and what should be done about it? Reinhold Vieth, PhD, a leading expert on vitamin D, provides the answers below.

New Discoveries

To produce adequate levels of vitamin D naturally, you must expose your skin (without sunscreen) to ultraviolet B (UVB) rays from the sun for about 15 minutes, as a general guideline, twice a week. If you use sunscreen, your body makes little or no vitamin D. Generations ago, when large numbers of Americans began working indoors—thus reducing their exposure to sunlight-their average vitamin D blood levels declined. Some food sources, such as egg yolks and sardines, provide small amounts of the vitamin.

More recently, average blood levels of vitamin D in the US have remained fairly constant. What has changed is the amount of scientific research pointing to the importance of the vitamin.

An overwhelming body of evidence shows that vitamin D not only affects the bones (by facilitating the absorption of calcium), but also may play a key role in fighting a wide variety of ailments, including cardiovascular disease... autoimmune diseases (such as rheumatoid arthritis, lupus and multiple sclerosis)...chronic bone or muscle pain (including back pain)... macular degeneration...and increased susceptibility to colds and flu.

A number of studies also have shown a link between adequate blood levels of vitamin D and lower risk for some types of cancer, including colon, lung, breast and prostate cancers as well as Hodgkin's lymphoma (cancer of the lymphatic system).

Important new finding: In a study of 13,000 initially healthy men and women, researchers at Johns Hopkins found that vitamin D deficiency was associated with a 26% increase in death from any cause during a median period of nine years.

How Vitamin D Helps

Recent scientific discoveries have demonstrated that vitamin D is critical for the health of every organ in the body. By acting as a sig. naling molecule, vitamin D helps cells "talk" to each other, which in turn helps control how they behave. Cellular communication is essential for healthy biology.

To understand the function of vitamin D think of paper in an office-you need paper to send memos and create reports. With enough paper, communication occurs easily. Without adequate paper supplies, the office may continue to function, but some important messages will not be communicated and mistakes will be made. Similarly, without enough vitamin D, your body is more likely to experience a breakdown of cellular communication that can lead to the conditions described above.

Are You At Risk?

Vitamin D deficiency is considered a "silent disease" because it can occur without any obvious signs. When symptoms do occur, muscle weakness and musculoskeletal pain are common.

Recent study: People with a severe vitamin D deficiency were more than twice as likely to die of heart disease and other causes than people with normal levels of vitamin D.

Among those at greatest risk for a vitamin D deficiency…

  • People over age 50. Beginning at about age 50, our skin progressively loses some of its ability to convert sunlight to the active form of vitamin D.
  • People with dark skin (anyone who is of non-European ancestry). Dark skin pigmentation offers some protection from skin cancer because it naturally filters the sun's cancer-causing ultraviolet B (UVB) rays. However, these are the same rays that we need to produce vitamin D.
  • People with limited sun exposure. Those who live in most parts of the US, except the extreme South, do not produce enough vitamin D from sun exposure in the winter months. Elderly people who may spend less time outdoors also are at increased risk for vitamin D deficiency.

Avoiding A Deficiency

Many doctors now advise their patients to receive a blood test that measures levels of 25hydroxy vitamin D—a form of the vitamin that acts as a marker for vitamin D deficiency. If you are concerned about your vitamin D levels, ask your primary care physician for the test—it typically costs $75 or more and is covered by some health insurers.

My recommendation: Get the test in the winter. If done in the summer, when you are likely to get more sun exposure, the test may reflect higher vitamin D levels than is typical for you at other times of the year.

As research confirming vitamin D's health benefits continues to mount, medical experts have raised the recommended blood levels for the vitamin-currently, levels of 30 nanograms per milliliter (ng/mL.) are considered adequate—but a more desirable range for most people is 31 ng/mL to 90 ng/mL.

The US adequate intake level for vitamin D (from food and/or supplements) is 400 international units (IU) per day for adults under age 70 and 600 IU for adults age 70 and older.

However, the consensus among vitamin D researchers is that most adults should be taking vitamin D supplements totaling 1,000 IU daily...and 2,000 IU daily might be even better for meeting the body's needs. Ask your doctor what the right dosage is for you. Either dosage can be taken along with a multivitamin.

It is nearly impossible to get enough vitamin D from diet alone. In the US, milk and other dairy products and some breakfast cereals are fortified with vitamin D. Other food sources such as salmon, sardines, egg yolks and beef liver also provide small amounts.

How difficult is it to get 1,000 IU of vitamin D per day from food? You would need to drink about 10 cups of vitamin D-fortified milk or orange juice...eat 30 sardines...or eat 55 egg yolks.

Helpful: When choosing a vitamin D supplement, look for vitamin D-3 (cholecalciferol). It is twice as potent as vitamin D-2 (ergocalciferol).

Caution: Because vitamin D is fat-soluble (stored in the body), consuming more than 10,000 IU daily (or 70,000 IU weekly) can lead to toxic reactions, such as weakness, nausea and vomiting.

Sunny Rooms Don't Help with Vitamin D

Ultraviolet B (UVB) rays, which stimulate the production of vitamin D in the body, do not pass through glass. In general, to produce adequate levels of vitamin D naturally, you must expose your skin-without sunscreen-to sunlight for about 15 minutes twice a week. It also is important to get vitamin D from food such as salmon, sardines, egg yolks, fortified milk and cereals, as well as from daily supplements. Vitamin D aids in the absorption of calcium, which helps form and maintain strong bones, and provides protection against osteoporosis. The vitamin also may protect against other disorders, including cardiovascular disease and autoimmune diseases, such as multiple sclerosis and rheumatoid arthritis.

C Is for Strong Bones

In a four-year study of 606 men and women, researchers found that men with the highest intake of vitamin C (314 milligrams daily) from food and supplements had the lowest levels of bone loss in the hip. Vitamin C is required for the formation of collagen, the main protein in bone. There was no similar finding in women, possibly because they already had adequate vitamin C levels.

For strong bones: Strive to eat five to nine servings daily of vitamin C-rich fruits and vegetables (such as strawberries and red peppers).

Save Your Sight

In a new study of 4,400 adults, those with the I highest levels of sun exposure and the lowest blood levels of the antioxidants zeaxanthin, vitamin C and vitamin E were four times more likely to have advanced age-related macular degeneration (AMD) than were those with less sun exposure and high antioxidant levels. AMD occurs when the macula (an area of the retina) deteriorates.

Self-defense: Eat at least five servings daily of antioxidant-rich produce, such as apples, oranges and leafy greens-and when outdoors, wear sunglasses and a wide-brimmed hat.

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