Consumer Reports has tested a supplement that is supposed to ease the pain of the millions of people who suffer from osteoarthritis. The results, they say, show that some brands are better than others.

That is important news for arthritis sufferers who turn to all sorts of products and treatments for relief.

Water exercise can be effective at soothing the debilitating pain of arthritis. Besides trying gentle exercise, arthritis sufferers spend millions on a variety of dietary supplements.

Consumer Reports' chief medical advisor, Dr. Marvin Lipman, said evidence shows at this point that there is only one type of supplement worth trying for osteoarthritis.

"There is some evidence that glucosamine plus chondroitin can provide some relief. But the results are mixed. At least it can't do much harm in most people," Lipman said.

Consumer Reports ran lab tests on 21 brands and found several did not contain as much of the active ingredients as promised on the label.

"Several of the products with problems came from dollar stores. So it's best to beware of discount brands," said Lipman.

Prices vary dramatically. Consumer Reports said the best deal is Kirkland Signature Extra Strength from Costco, which provides the recommended dose for just 25 cents a day.

Four other choices that did well in Consumer Reports' tests are:

Spring Valley Double-Strength Glucosamine Chondroitin from Wal-Mart.

Triple-Strength Glucosamine Chondroitin from Target.

Vitamin World's Double-Strength Glucosamine Chondroitin.

Vitasmart Double-Strength Glucosamine Chondroitin from KMart.

The latest studies show that not all arthritis sufferers will get relief from glucosamine chondroitin. If you want to try it, Consumer Reports said it can take a full three months before you know whether it offers any relief.

While glucosamine chondroitin appears safe for most people, there are some exceptions. Consumer Reports said you should avoid the supplement if you are allergic to shellfish, or if you take a blood thinner or have a clotting disorder. If you are a diabetic, you have to monitor your sugar level more closely.

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