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Oral Joint Supplements
David Ramey, D.V.M.
Equine Advisor to the Task Force For Veterinary Science
If you've been into a tack store lately, you may have noticed that something approaching two-thirds of the store is devoted to oral supplements meant to combat the bad effects of arthritis. The products are wonderfully packaged, heavily advertised, impressively endorsed and sometimes even recommended by veterinarians. That being said, at this point in time, no one knows how or if they work in horses.
Oral supplements usually contain at least one of two substances (and sometimes both). These substances are chondroitin sulfate and another substance called glucosamine (it can be chemically constructed in several ways; glucsoamine hydrochloride is one common form found in many equine products). Chondroitin sulfate is the primary GAG found in joint cartilage; experimentally, orally administered chondroitin sulfate has been shown to have some anti-inflammatory effects in some species (including man but not yet in the horse). On the other hand, at least one human study showed that chondroitin sulfate isn't absorbed from the intestinal tract and that any direct action of chondroitin sulfate on the joint cartilage was impossible. Absorption studies on horses haven't been published yet. However, from all the studies that have been published, one thing seems certain with these products; they seem incapable of hurting a horse.
Glucosamine is a complex sugar molecule from which the proteoglycans that are found in normal joint cartilage are made. It's actually found almost universally in small amounts in most foods (and in larger amounts in foods that contain cartilage). Research done on people with osteoarthritis of the knee who took glucosamine orally showed that it was as effective as ibuprofen, a commonly used non-steroidal anti-inflammatory drug, at controlling the pain and soreness associated with the disease. Other studies have shown that glucosamine has a direct anti-inflammatory effect. Furthermore, there is evidence (in humans) that glucosamine is absorbed from the gastrointestinal tract.
Glucosamine also increases the production of GAGs by the joint cartilage in the test tube. This intriguing finding brings up the question of whether glucosamine could be used to help "restore" joint cartilage that has been damaged or to promote cartilage health by helping it to maintain itself. If it could do these things, there's no reason why every horse (indeed, every person) shouldn't be taking the stuff. However, even when you don't consider this aspect of glucosamine therapy, it has shown the most impressive results of the oral supplements that are used to treat arthritis so far.
To date, there have been only a few studies that have been performed looking at the ability of oral joint supplements to treat joint inflammation in a horse, however. In one study, horse knee joints were irritated by the injection of a foreign substance. They were treated by injection of intravenous hyaluronan, intramuscular PSGAG and by a heavily advertised brand of oral joint supplement. The first two treatments helped relieve the signs of inflammation (the PSGAG seemed better). The oral joint supplement had no apparent effect. This study certainly isn't the final word about oral joint supplements and it may not even be the best experimental model in which to investigate arthritis (for example, injecting an irritating substance into a joint certainly doesn't mimic the changes that occur in osteoarthritis). Nonetheless, the results of this study showed that two injectable products seemed to help relieve joint inflammation; the oral one didn't.
However, three other studies evaluating oral joint supplements in horses either have been or are about to be published. The first was a clinical trial performed on horses with osteoarthritis. The 25 horses in the study all appeared to improve after receiving an oral joint supplement product; best of all, the improvement was noted in just two weeks after the onset of therapy. The weakness of this study is that it wasn't "double blinded;" that is, the examiners knew that the horses they were examining were receiving treatments (and their evaluation was potentially biased as a result). Still, the study certainly suggests that there is a reason to evaluate these products in horses more fully. A second recently reported study indicated benefit from the use of an oral joint supplement in the treatment of navicular syndrome (a condition which has many features that mimic the changes that occur in osteoarthritis). Yet a third study on horses being supplemented with an oral joint product showed an increase in stride length and a decrease in lameness in 25 horses that were treated with it. There are other studies ongoing which will hopefully make the potential benefits of these supplements a bit more clear.
Given the relative lack of research on horses, as a potential purchaser of glucosamine and/or chondroitin sulfate products, there are other questions that you should be asking. For example, one question might be, "Does the product that I'm buying contain what the label says that it does?" According to research at the University of Maryland, the answer is, "Not necessarily." In fact, researchers at the University tested 27 glucosamine or chondroitin-sulfate products and found that a number of them didn't have the amounts of the product in them that the label said they did. The actual content can even vary from month to month as different batches of product are released. (Unfortunately, the names of all of the products used in the Maryland study were not released).
Furthermore, how do you know which product do you choose? There's a lot of advertising hoohah about where the glucosamine and chondroitin sulfate that's found in these products come from. Some of the products are derived from the windpipe of a cow. Another product is made from shark cartilage (the fact that the product comes from shark cartilage offers some distinctive packaging opportunities, when compared to those offered by products derived from cows). Yet another product comes from sea mussels (and smells like it, too). At this point in time, it's not clear that the source of your horse's glucosamine and chondroitin sulfate makes any difference whatsoever, however. And again, most of these products are not rigorously tested for the actual content of their active ingredients.
Should you use oral joint supplement products to help treat or prevent arthritis problems in your horse? At this time, there's no clear answer to that question. Research does seem to indicate that chondroitin sulfate and glucosamine do have some promising anti-inflammatory and joint protective effects, particularly if used early in the treatment of arthritis. There's no question that the supplements don't seem to be able to hurt your horse (your pocketbook is another matter). There's also no question that many people (including veterinarians) recommend them. But there's also no evidence to date that they are consistently effective in relieving inflammation or promoting cartilage maintenance in horses or in any other species. However, oral joint supplements are almost certain not to work in horses with advanced osteoarthritis, since these horses may not have much cartilage left to restore. Further muddying the waters is the fact that there are no doses of these products that have been established.
Is all this hubbub about oral joint supplements confusing to you? Well it should be. The biggest problem with these products is that they are being marketed as a nutritional supplement with implied medical benefits. Medical products fall under the jurisdiction of the U.S. Food and Drug Administration; nutritional supplements don't. Medical products have to be rigorously tested, must be labeled properly and have to show evidence of effectiveness; nutritional supplements don't. Ultimately, the only way that the buying public is going to find out if oral joint supplements are effective treatments for arthritis is to demand that the FDA get in and classify these substances as drugs and monitor them accordingly. Then (and only then) you will be able to be reasonably sure that the products are properly labeled, adequately tested and reasonably effective. Until then, whether these supplements are an important weapon in the war against arthritis in your horse or if they are just another opportunity for you to spend money on him is going to be purely a matter of guess work, trial and error.