There has been such an explosion in oral supplements for joint support with various new ingredients that it's hard to keep up with them all. One ingredient that shows up in more products all the time is hyaluronic acid (also called HA).
Hyaluronic acid is a member of a group of compounds called glycosaminoglycans. These substances are what give skin its elasticity, cartilage its "give," and fluids their lubricating properties. Hyaluronic acid is found both in joint fluid and the cartilage itself. It is a major factor contributing to the slippery feel of joint fluid. In inflamed joints, breakdown of HA makes the joint fluid more watery and less able to keep the joint "greased." Inside the cartilage itself, hyaluronic acid combines with another glycosaminoglycan called aggrecan to form a complex that helps trap fluid in the cartilage and keeps it flexible and resistant to being overly compressed.
In the joint, hyaluronic acid is produced both by the chondrocytes, which are specialized cells inside the cartilage, and also by the synovial membrane. In an inflamed joint, enzymes called the hyaluronidases cause the breakdown of hyaluronic acid. High activity of these enzymes is associated with arthritis. Interestingly enough, short chains of hyaluronic acid, produced in the process of breaking down HA, actually contribute to inflammation in the joint by triggering other pathways of inflammation. This is why chronic arthritic problems can become self-perpetuating cycles.
Interest in hyaluronic acid for treating arthritis in horses dates back to the early 1970s, when "black market" hyaluronic acid from Europe started showing up on racetracks, first in the Standardbred world, then among Thoroughbreds. At that time, all hyaluronic acid used was injected directly into joints. It didn't take long for the amazing effects of this treatment to become widely known. Before hyaluronic acid, joint problems were treated primarily with corticosteroids. This worked for a while, but when done frequently and in high doses, the steroids themselves started to cause problems by inhibiting the metabolism of joint cells. Infections of the joint and secondary metabolic effects also were risks with corticosteroids.
How Do They Work?
How joint supplements work is still a bit of a mystery. The effects they have on cell cultures in a laboratory may not be what they are actually doing inside the body. One common effect appears to be to "tie up" the enzymes that break down joint fluid and cartilage. If the supplement can get the attention of these destructive enzymes and occupy them, the balance inside the joint has a chance to get on top of the inflammation. Hyaluronic acid may also have important "cell signaling" effects, meaning it could help stimulate the production of other glycosaminoglycans
It wasn't long before American companies jumped on board the HA bandwagon and FDA-approved hyaluronic acid products became available. The high-molecular-weight products worked better than the less expensive, low-molecular-weight ones that had shorter chain lengths and were more likely to make joints painfully swell for a few days afterward. In those days, it was thought that this was because they weren't as purified as the more expensive products. We now know it was probably because low-molecular-weight hyaluronic acid actually causes an inflammatory response in the joint.
The 1980s and most of the 1990s represented the heyday of hyaluronic acid joint injections. The next big development was when the product Legend came on the scene in 1991. Legend is an intravenous hyaluronic acid that is carried by the blood stream to the joints. While some were skeptical, the experiments done to satisfy the FDA's requirements showed very clearly that it did indeed work. In those studies, joint inflammation was experimentally induced, and the equine test subjects were split into two groups-one treated with intravenous hyaluronic acid and the other was an untreated control group. The treated horses did significantly better in terms of pain, freedom of movement, and even the actual condition of their cartilage. You can read the details of those studies online at http://www.fda.gov/FOI/1392.htm.
The advantage to the intravenous product was that it completely removed the low, but real, risk of causing a joint infection or accidentally damaging the joint cartilage with a needle. In fact, it worked so well that nowadays IV injection is used more often than direct joint injections.
Effective, yes-but also expensive! Intravenous hyaluronic acid is a prescription drug, so it also requires a veterinarian fee. Moving forward to the 21st century, the first oral hyaluronic acid treatment for horses was released: hyaluronic acid in a gel form. This sounded like a great idea-but would it work? Could it even be absorbed?
At the time this product was introduced, there were no good studies to show absorption. However, orally given hyaluronic acid was being used experimentally as a carrier for insulin absorption. Proof of absorption finally emerged at the 2008 meeting of the Federation of American Societies of Experimental Biology. Radioactively labeled high-molecular-weight HA was fed to mice and dogs. By measuring radioactivity in the blood and body tissues, it was found that even this large, high-molecular-weight molecule could be absorbed (with about 13% of the dose making its way into the body).
Getting back to horses and oral hyaluronic acid: A study published in 2006 performed at the Rood and Riddle Equine Hospital in Kentucky looked at the effects of using hyaluronic acid gel postoperatively in yearlings who had surgery for osteochondrosis problems in the hock. The study included 48 yearlings, with half receiving the HA gel while the other half did not. They found significantly reduced joint swelling in the treated horses.
The dosage used for the Rood and Riddle study was 100 mg. A study presented at the 2003 meeting of the Matrix Biology Institute (a nonprofit organization devoted entirely to hyaluronic acid research) reported that the same 100 mg dose given to racing thoroughbreds reduced the number of times vets were asked to examine them for lameness.
My personal experience with hyaluronic acid is that it is extremely effective orally for getting rapid control of joints that are acutely inflamed, hot, and painful. Improvements are obvious within 24 to 72 hours. The gel and liquid forms seem to work more quickly. Hyaluronic acid is also now widely available as a powder. This form has not been studied to see how it compares for absorption or effectiveness.
Is HA For Your Horse?
If you're already using a joint supplement, should you switch to one containing hyaluronic acid? This ingredient definitely benefits horses with joints that are hot and swollen from a flare up of an old problem, an entirely new problem, or from being worked hard and regularly. If your horse has more of an old arthritis with a largely stable pattern of stiffness and no dramatic changes, it's a little more difficult to predict if HA will help. The best advice we can give you is that if your current joint supplement isn't giving you the results you had hoped for, try adding hyaluronic acid. You could try buying an HA-only product first and adding this to your current supplement, or you could switch to a combination product that contains hyaluronic acid and doses of other ingredients that are similar to your current supplement. The object here is to avoid making any changes except for the addition of the HA.