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The Truth Behind the Top 10 Dietary Supplements

What you need to know about the most popular dietary and nutritional supplements on the market.

Vitamin C

Vitamin C is often taken in an effort to ward off colds, though there's little proof this works.

"There is scant evidence it may decrease the intensity or duration of colds, but it won't do any harm up to about 1,000 milligrams a day," Grotto says. Because it is a water-soluble vitamin, excess amounts are excreted.

Your health-care provider may tell you to take vitamin C if you have a wound that's healing. But wound otherwise, go for food sources.  Rich sources include oranges, peppers, grapefruits, peaches, papayas, pineapples, broccoli, strawberries, tomatoes, and melons.

Glucosamine and Chondroitin

These supplements are often taken by people with joint pain.

In a study published in the The New England Journal of Medicine, these supplements, taken alone or in combination, were not found to provide significant relief from osteoarthritis knee pain among all participants. However, results in a subgroup of study participants with moderate to severe pain showed the combination may be effective.

While the evidence is not conclusive, some rheumatologists say many of their patients find relief from the combination.

"About 40% of my osteoarthritis patients benefit from taking 1,500 mg of glucosamine and 1,200 mg chondroitin sulphate a day (for) four to eight weeks," says Kaiser Permanente rheumatologist Eduardo Baetti.  But "most patients are also taking pain relievers, such as Tylenol."

Homeopathic Medicines

These are not technically dietary supplements, but are nonetheless a popular category.

Homeopathy, or homeopathic medicine, is a medical philosophy dating back to the late 1700s. It's based on the idea that our bodies have a self-healing response. So, the theory goes, if certain a substance causes a symptom in a healthy person, giving that person a very small amount of the same substance may cure the symptoms.

The National Institute of Health's National Center for Complementary and Alternative Medicine web site notes that studies on homeopathy have been contradictory. Some have suggested the results are similar to a placebo effect, while others have found positive effects that are not readily explained in scientific terms.

"Homeopathics are benign in general because they are so dilute it is unlikely they will cause any harm if used properly," says Grotto. "But the explosion in this category includes cleansers [products marketed as kidney, liver and other organ cleansers] and products that misuse the term and are not really homeopathic."

He cautions users to consult health care professionals, and not to attempt to treat or diagnose conditions that require professional care.

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