Most people get insufficient Vitamin D, but extra supplements may not be needed

Tuesday, January 12, 2010

Vitamin D is shaping up to be the nutrient of the year, if not the decade.

Evidence is mounting that the vitamin is vital to the health of a wide variety of body systems. Studies suggest that the vitamin plays an important role in reducing the risk of a host of illnesses, notably osteoporosis and possibly certain cancers and autoimmune, infectious and cardiovascular diseases.

Unfortunately, typical blood levels of Vitamin D have dropped over the past decade to the point that, according to a recent study, 77 percent of Americans have insufficient amounts. Some of the decline may stem from new testing methods. But we also go outside less often and, when we do, it's under cover of hats and sunscreen. Other factors include obesity (fat holds onto Vitamin D, making it less available to the rest of the body) and the reduced consumption of fortified dairy products, one of the vitamin's main dietary sources.

Although Vitamin D has garnered lots of press of late, many important questions remain unanswered. Official recommendations for intake are widely considered to be too low, for example, but there's no consensus on how much is enough. Some experts recommend soaking up sunshine, while others say it isn't worth the risk of skin cancer.

To make sense of it all, Consumer Reports posed some questions to several experts in Vitamin D research.

-- How much do I really need? Based on solid evidence linking Vitamin D to strong bones and a reduced risk of fractures, experts say that most people should get at least 800 to 1,000 international units daily. Some nutrition researchers say that adults may need twice that amount to raise blood levels of the vitamin as high as those associated with a reduced risk of other conditions, such as heart disease and cancer. But evidence in these areas is mixed and often contradictory. One point of agreement: The current dietary reference intake (DRI) -- which ranges from 200 to 600 IU daily for adults, depending on age -- is too low.

-- Do I get enough from sunlight during my daily walks? Not as much as you might think. A 2008 review published in the American Journal of Clinical Nutrition found that people's answers to questions about their sun exposure didn't correlate very well with their Vitamin D status. While it's true that ultraviolet light causes a chemical in the skin to be converted into Vitamin D, many factors can affect the process.

If you walk in the early morning or late afternoon, for example, the sun is usually not intense enough to stimulate production of the vitamin. And if you live in the northern half of the United States, sunlight never reaches sufficient intensity during the winter to generate Vitamin D. Regardless of your locale, other factors, including sunscreen and protective clothing, and being older or overweight, can slow or even shut down your skin's Vitamin D factory. Darker skin also hinders D production; the latest population statistics show that only 3 percent of African Americans have healthy blood levels of it.

-- Can I get enough from food? Probably not. For the most part, the only foods naturally rich in the vitamin are fatty fish, such as herring (1,300 IU in a three-ounce serving); salmon (up to 850 IU in a serving of wild salmon, much less in farmed varieties); and mackerel, sardines and tuna (about 200 to 300 IU a serving).

Dairy products as well as some breakfast cereals, orange juices, soy-based foods and other products are fortified with about 100 IU a serving. But most people don't eat enough of those foods to consistently cover all of their requirements.

-- Do I need a special supplement? Not necessarily. Manufacturers of multivitamin and calcium supplements have increased the amount of Vitamin D in many of their products to 800 IU. If you don't already take one of those, you can buy Vitamin D supplements relatively inexpensively. Consider looking for ones that contain Vitamin D3, which may be a more potent form than D2.

-- Can I overdose on it? Not unless you go out of your way to take megadoses in supplements. You can't get too much Vitamin D from sun or food.

-- Do I need a Vitamin D test? Testing is necessary only if you have a condition that's clearly linked to Vitamin D deficiency, notably weak bones, or celiac disease or other ailments that impair the body's ability to absorb the vitamin from food. Make sure your doctor orders a test for 25- hydroxyvitamin D. Taking supplements at the recommended levels will correct any deficiency.

Copyright 2009. Consumers Union of United States Inc.

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