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Vitamins can be too much of a good thing, experts warn

Christan M. Thomas • Jul 15, 2007 at 12:00 AM

Wandering through the vitamin aisle, the sheer number of bottles can be a little overwhelming.

With dozens of choices from multivitamins to nutritional supplements, knowing what to take - or even if taking a vitamin is necessary at all - becomes a guessing game for many health-conscious consumers.

Information from the Mayo Clinic on vitamin and mineral supplements states that it is important to remember that vitamins should not be taken in place of eating a healthy diet, since eating a variety of healthy foods provides the best source, as well as the best absorption for vitamins and minerals. Many people do not, however, receive all of the nutrients they need from diet alone because they either can't or don't eat enough, or they can't or don't eat a variety of healthy foods.

According to a position paper from the American Dietetic Association on nutritional supplements, besides the "best practice" of choosing a wide variety of healthful foods, "additional nutrients from fortified foods and/or supplements can help some people meet their nutritional needs."

While Melisa Heber, a clinical dietitian with Wellmont Holston Valley Medical Center, said the best way to get a full range of vitamins and minerals is from a balanced diet, she also adds that those who are unable to eat such a diet - including people with an extremely busy lifestyle or a limited diet; vegetarians; women of child-bearing years; those on a low-calorie diet and the elderly - can benefit from taking a multivitamin with levels at or below 100 percent of the daily recommended allowance.

"I do not recommend that people take vitamins in general," said "What I recommend is that they eat a healthy diet. ... If you eat a good, balanced diet you don't need supplements.

"The vitamin supplement is not going to fix everything that's wrong with a diet. It's mythical thinking to solve everything that's wrong with your diet by taking a vitamin. ... Generally taking a one-a-day won't hurt anything. It might balance out a few things."

Consumers can search the ADA Web site, www.eatright.org, for the words "vitamin supplements" and then click on a quiz that can help decide whether taking a multivitamin is necessary.

Of course, checking with a doctor before starting any type of nutritional regiment is advisable. Heber said people should definitely check with their doctors before beginning supplements other than a daily multivitamin.

Just as having a vitamin deficiency can cause health problems, people can also take too much of a good thing.

High levels of vitamins and minerals can cause certain medications to lose effectiveness or even lead to serious drug interactions. Toxicity can also occur when large quantities of a particular vitamin or mineral are ingested. Though symptoms of toxicity vary depending on the vitamin or mineral in excess, effects can include hair loss; dry skin; depression; blurred vision; headaches; kidney and heart disease; nausea; kidney stones; and insomnia. Fat soluble vitamins carry a greater risk of causing toxicity.

Heber said taking one or even two multivitamins a day will probably not raise levels even near that of toxicity. Taking separate supplements without a doctor's advice, however, can cause these issues.

"When we eat a healthy, balanced diet, we cannot get an excess of a vitamin or mineral to harm us, unless we have some kind of a disease or problem in the body," Heber said. "There are certain things in food that decrease absorption, certain things that increase it and they play off each other. So, if you just pick a (certain) vitamin and take it, you're not getting the best absorption because you might need another vitamin to improve absorption or to offset it. ... It's always a good thing to run it by your doctor."

Besides checking with your doctor, the Mayo Clinic offers some tips to help avoid any unwanted effects and still reap the health benefits of vitamins.

•Check the package label of vitamins and supplements. Read labels carefully. Product labels list active ingredients, nutrients included, serving size and the amount of nutrients in each serving.

•Avoid supplements that provide "megadoses." In general, choose a multivitamin-mineral supplement that provides about 100 percent of the daily value of all the vitamins and minerals, rather than one containing high percentages on one vitamin and low does of another.

•Look for "USP" on the label. This ensures that the supplement meets the standards for strength, purity, disintegration and dissolution established by the testing organization U.S. Pharmacopeia.

•Beware of clever marketing. Synthetic vitamins are usually the same as "natural" vitamins, but may cost less.

•Look for expiration dates. Dietary supplements can lose potency over time, especially in hot and humid climates. Do not buy supplements without expiration dates and throw away any expired pills.

•Store all vitamin and mineral supplements safely. Store dietary supplements in a dry, cool place. Avoid hot, humid storage locations, such as the bathroom. Also, store supplements out of sight and away from children.

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