Studies increasingly are suggesting the value of vitamin D – often known as the sunshine vitamin, because that’s one way you can obtain it – in everything from bone metabolism to maintaining muscle strength, immune function, reducing hypertension and possibly even playing a role in prevention of cancer and autoimmune disease.

Summer is a time when most people finally get enough of this vitamin due to their sun exposure, and also help build stores of it in their fat for use during the dark days of winter. But research has suggested that, for whatever reason, as many as a billion people around the world may now be vitamin D deficient, posing possibly serious threats to their health.

“The old theory was that if you had enough vitamin D to prevent rickets and osteomalacia, two skeletal disorders, you were okay,” said Victoria Drake, a research associate in the Linus Pauling Institute at Oregon State University, and manager of its “Micronutrient Information Center. But new research is now raising our awareness about the possible relationships between vitamin D and cancer, particularly colorectal, breast, ovarian and prostate cancers. There are also potential links to cardiovascular disease, and autoimmune diseases such as multiple sclerosis and rheumatoid arthritis.”

Many of the studies are observational, Drake said, and more work needs to be done with randomized, double-blind, placebo-controlled clinical trials. Experts still argue about how much vitamin D is enough, and some feel that the optimal amount is several times higher than the adequate intake level set by the Food and Nutrition Board of the Institute of Medicine, which is 200 international units per day for adults ages 19-50.

What’s clear, however, is that many Americans are not getting even those minimal amounts, especially those with dark skin colors – one study reported that 42 percent of African American women were vitamin D deficient.

As a result, Drake said, many doctors are increasingly starting to test their patients for deficiency of this vitamin, especially in the temperate zones above 40 degrees latitude – a line running roughly from Philadelphia to Denver and through Northern California. That includes New York City, Boston, Chicago, Detroit, Seattle and many other of the nation’s most populous cities. Residents of the Pacific Northwest, with its northern latitudes and eternally cloudy winters, are especially vulnerable. Inexpensive supplements are frequently prescribed.

“My own doctor said that he frequently tests for vitamin D status, and that vitamin D deficiency is prevalent in his patient population,” Drake said. “Experts are now talking about a phenomenon they call ‘Vitamin D Winter.’”

One recent study referred to vitamin D deficiency as “a major unrecognized epidemic in the older adult population” and recommended routine blood testing for adequate levels.

Open to speculation, but little in the way of proof, Drake said, is that deficiencies of vitamin D may have worsened in recent years as more people became aware of the risks of skin cancer and aggressively avoided sun exposure or used sunscreen lotions, on themselves and their children. Experts still agree that a fairly modest amount of sun is enough – perhaps 10-15 minutes of exposure on your arms and face about three times a week. Sunburn should of course be avoided and a tan clearly isn’t necessary – but some real sun exposure probably is.

Alternatively, you can also get vitamin D from some foods, including vitamin fortified milk and some cereals or breads – assuming you don’t have a diet rich in oily fish. For higher levels, supplements are usually necessary.

Among the recent findings and observations about vitamin D:

• Vitamin D is a fat-soluble vitamin that functions as a hormone in the body, regulating calcium metabolism.

• Most people living above 40 degrees latitude do not obtain enough vitamin D from about mid-November to early March.

• Infants who are exclusively breast-fed, and are not supplemented with vitamin D, are at high risk of vitamin D deficiency, because human milk generally doesn’t have adequate levels.

• People with dark-colored skin have significantly less ability to synthesize vitamin D from sunlight, as do the elderly.

• Obesity increases the risk of vitamin D deficiency because obese individuals cannot easily access the vitamin D stored in body fat.

So if adequate levels of vitamin D are critical to your health, how much is enough? Depends on who you ask, Drake said. The official government recommendation is 200 I.U. per day – although moderate sun exposure might provide about 100 times that much. Many multivitamins provide about 400 I.U. per day, and it’s generally accepted that levels up to 2,000 I.U. per day pose no health risk. Some studies under way with pregnant women are giving them 4,000 I.U. per day in supplements.

One study last year indicated an adequate level of vitamin D, produced by daily supplements of up to 2,000 I.U. per day, might prevent 30 percent of the cases of breast cancer and 50 percent of the colon cancer in the United States – at extremely low cost and with few or no adverse effects.

The Linus Pauling Institute recommends a multivitamin supplement with at least 400 I.U. of vitamin D for most healthy adults, and twice that amount for anyone over age 50. Additionally, at least 10-15 minutes of sun exposure on the arms and legs, or face and arms, at least three times weekly, between 11 a.m. and 2 p.m. during the spring, summer and fall may help residents of temperate latitudes avoid vitamin D deficiency at the end of winter.

“There’s a lot we still have to learn about this micronutrient, but it’s already clear the role it has in optimal health, and that a lot of people don’t get enough,” Drake said. “Many people may need to consider supplements, especially in winter. And one thing we would say is, don’t be afraid of getting at least a little sunshine. It’s good for you.”

Source: Oregon State University