Oral Joint Supplements: Cure-all or Expensive Fad?

Take-home message

• Joint supplements are classified as "nutraceuticals." Nutraceuticals are products sold under the premise of being a dietary supplement, but for the expressed intent of treatment or prevention of disease.
• Most consumers utilize oral joint supplements to heal or prevent joint damage in athletic horses.
• Oral joint supplements contain "building blocks" of normal, healthy joint cartilage.
• The efficacy of oral joint supplements has not been clearly documented in horses.
• Problems may exist with oral joint supplements not containing the actual amount of active ingredient indicated on the label.

The obvious intent of a performance horse is to perform or compete in some manner. Athletic competition requires horses to run, jump, turn, start and stop placing an enormous strain on the skeletal system. One reason a performance horse may fail to reach its athletic potential is because of lameness. There are many reasons horses become lame. Injuries to and diseases of the joints are common causes of lameness. Since joint problems can be a limiting factor in athletic horses, care and maintenance of joints is a major concern for trainers, grooms, owners and veterinarians.

Joint health is an evolving science. Research scientists are investigating many new equine joint therapies. A relatively new approach to joint health is the use of oral joint supplements. If you have read any popular press horse magazine or visited a tack/feed store in the last five years you have been exposed to "joint supplements". Despite their prevalence in the market, much confusion exists regarding these products. The following is a brief summary of some of the information available on joint supplements.

Joint Supplements as Nutraceuticals

Joint supplements are loosely classified as nutracueticals. The term "nutraceutical" combines the word "nutrient" (a nourishing food or food component) with "pharmaceutical" (a medical drug). The word nutraceutical has been used to describe a broad list of products sold under the premise of being a dietary supplement (i.e. a food), but for the expressed intent of treatment or prevention of disease. In the case of joint supplements, they are sold as dietary supplements but with a twist.

The twist being the claims (usually made by manufacturers) of their ability to aid in health of the equine joint. A potential difference between a feed and a nutracuetical is that a nutracuetical is unlikely to have an established nutritive value. Feeds are required to have nutritive value and are accountable, via labeling, for these values. Another difference between a feed (food) and a nutracuetical is that feed is "Generally Recognized As Safe (GRAS)." Nutraceuticals may contain substances that are "natural" but may not be generally recognized as safe (GRAS). The primary stumbling block in adding the "active" compounds found in joint supplements into horse feed is that these substances do not have a GRAS statement on file with the feed regulatory agencies. Thus inclusion of the joint supplement in the feed and listing its name on the feed tag are illegal simply due to the lack of established safety data.

The other component of the definition of nutraceutical includes the statements "for disease treatment and prevention" and "administered with the intent of improving the health and well-being of animals." When a dietary supplement, nutracuetical or other feed is intended to be used for the treatment or prevention of disease, in essence it "becomes" a drug. Drugs are subject to an approval process prior to marketing. To be approved, a drug must demonstrate safety and efficacy for its intended use. Drugs that are not properly approved are subject to regulatory action.

From this discussion, it seems joint supplements fall somewhere in between food and drug. They have many advantages over either food or drug since they are not required to list all ingredients and nutrient profiles as required by feeds, and in many cases are intended to treat or prevent disease without first undergoing proper drug approval. Determining if a product is a food, or is subject to regulation as a drug, is a function of the manufacturer's claims that establish intent.

The Goal of Joint Supplements

With vague label information, it is difficult to determine what the manufacturers of joint supplements intended as an exact function for their products. It is not difficult however to determine what is implied and expected by horse owners who buy the products. In most cases joint supplements are fed to horses for one of two purposes. The first intended purpose is to heal the lame. Stated another way, make unsound horses sound again. Unfortunately, horses can be lame for a number of reasons and a single joint supplement could not possibly be successful in treating all causes of lameness. Even with other more studied approaches to treating lameness we don't expect 100% success in treatment.

The second intended purpose consumers have for oral joint supplements is to prevent joint problems from ever occurring. Unfortunately, many horse owners have suffered through seeing a talented horse's career cut short due to joint problems resulting from injury. They have since vowed to do "everything possible" to prevent the problem from occurring in other performance horses. Again, this expectation may be unrealistic due to the sheer number of opportunities that athletic horses have to take a bad step and become injured.

Do oral joint supplements work in horses? Some horse owners swear by the results obtained by feeding joint supplements, while others can't honestly say they saw much of an effect. With the unrealistic goals that both consumers and manufactures have placed on joint supplements, horse to horse variability and different under lying causes of lameness explain at least some of the difference of opinion as to the effectiveness of oral joint supplements. The key to understanding the potential for a joint supplement to be effective is to first understand the basics of bone movement that occur at the joint. Second, an understanding of tissues involved and normal joint function will provide rationale for many of the ingredients utilized in joint supplements.

The Equine Joint

Anywhere that bones meet in the body is called a joint. A joint allows controlled movement of bones relative to each other, thus allowing the skeleton to move and ultimately the leg to bend. The equine joint endures incredible pressure in resisting the damaging effect that can occur when bones collide. Normal horse movement begins with muscle contraction. Shortening of muscle fibers move the bones via tendons that attach muscle to bone. An excellent description of normal joint movement was written by Karen Briggs and published in The Horse magazine (March, 1997 and November, 2000). The following is a summary of that description taken with permission from The Horse.

In a normal, healthy joint, the ends of the bones are coated with a thin layer of friction reducing articular cartilage. They are surrounded by a joint capsule with a tough outer layer (to connect the bones and protect the joint) and a permeable inner layer, or synovial membrane, which secretes synovial fluid and allows the passage of nutrients and other elements from the blood stream. Synovial fluid, a slippery, viscous liquid that many researchers describe as being about the same consistency as egg whites, fills the joint capsule, nourishes the articular cartilage, and provides essential lubrication.

Synovial fluid is a nutrient-rich brew that contains proteins and enzymes, water, leukocytes, and the key ingredient sodium hyaluronate, which is responsible for the fluid's elastoviscous qualities. Sodium hyaluronate (fromerly known as hyaluronic acid) is a negatively-charged sugar chain, or glycosaminoglycan (GAG), which arranges itself in complicated coils, adapting to the pressure changes in the joint capsule as the horse moves. It assures the unhindred passage of metabolites to and from tissues throughout the joint, and also serves as a stabilizer and shock absorber for the structures that are undergoing continual, changing mechanical stresses.

Articular cartilage, the other main shock-absorbing component of a joint, is an efficient but flawed structure. Its structural framework is a web of collagen fibers, with cells called chondrocytes scattered along the matrix. Chondrocytes produce giant proteoglycan molecules that resemble bottle brushes and bind the GAG's. The GAG's in turn extract and loosely hold large amounts of positively charged water molecules. When cartilage is damaged, there is a decrease in the number of GAG's; therefore, the cartilage holds less water.

Among the talents of cartilage: it conforms to the bone surfaces for a tight fit between weight-bearing bones; it spreads pressure evenly over a broad area; and it "manages" the water in its matrix, squeezing it out when the joint is under pressure, and drawing it back in when the joint is "unweighted." This in and out movement of the fluid transports nutrients throughout the cartilage. Cartilage also, in a way, acts like a sponge, conforming to loading demands by changing its shape and size, and regaining its original shape when the pressure is off. This "squeeze film lubrication" is the most important part of cartilage on cartilage lubrication. This cartilage lubrication is much like hydroplaning-there is a thin coat of water between surfaces acting to decrease the coefficient of friction.

But here's the downside: cartilage is one of the body's most primitive structures. It has no blood or nerve supply of its own, so cartilage has little or no ability to heal or repair itself. Only in rare cases when the cartilage is torn directly off the bone can healing take place (because the resulting space allows capillaries to break through and patch up the holes with fibrocartilage). Even then, the repair work is substandard and won't stand up to repeated stresses. As a result, although cartilage performs admirably under normal conditions, it only takes a 5-10% overload of work stresses to begin the process of cartilage breakdown.

Joint Damage and Why

Lameness can result from damage to any of the tissues associated with the joint. If ligaments, tendons or muscles that help stabilize joints become disrupted due to injury, instability of the joint can result. This ultimately results in a change in the normal range of motion of a joint and lameness. Likewise, disease of the supporting bone can lead to collapse of the joint surface and painful lameness. Damage to the articular cartilage such as breakdown of collagen and loss of proteoglycan result in weakened cartilage. This weakened cartilage develops cracks and holes and looses its smooth articulating surface resulting in lameness again. Likewise, damage to the synovial membrane and changes in the makeup of the joint fluid result in alternations in normal joint viscosity and still another reason for lameness. So what is the underlying reason for joint damage? The answer is quite simple -"inflammation".

Inflammation is normally a protective mechanism initiated by the body in response to injury. It is often localized to a particular area of the body and begins as a result of injury to or destruction of body tissue. The purpose of inflammation is to destroy, dilute or isolate both the injured tissue and/or any foreign material. It is the initial response in a series of events that lead to the attempted repair of the injured tissue. Inflammation causes blood vessels to dilate and allows fluid and cells to leak out. The cells that are released into tissues during inflammation are mostly white blood cells. In turn white blood cells release a variety of chemicals and enzymes into the inflamed area.

The inflammation response in a joint is also a process designed to breakdown and remove injured or foreign material. The process of breaking down and removing the foreign bodies from the area changes the chemical makeup of the fluid in the joint, introduces excess fluids and a high concentration of destructive enzymes and prostaglandins into a closed area (the joint capsule). This destroys the lubricating GAGs. The synovial fluid begins to lose viscosity. The chondrocytes eventually suffer from a compromised nutrient supply, can't keep up with repairs, and the cartilage develops damaged areas opening the bone ends to direct trauma. The bone responds with a defense that only causes further destruction, it lays down new bone to strengthen the surface (sclerosis) and extends its margins in the form of bone spurs. If left unchecked, inflammation will totally destroy the joint as a disease called arthritis.

Treatment Strategies

Many options exist for treating joint disease in horses. The major treatment goals are to reduce inflammation, improve joint fluid, and/or to improve cartilage. Treatments to accomplish these goals generally fall into two categories: physical therapies and medical therapies. Physical therapies include rest, bandaging, application of heat, application of cold, and mild, controlled exercise to maintain range of motion. Forty years ago, medical therapies to treat joint disease were limited to liniments, blisters, sweats, poultices, application of DMSO (Dimethyl Sulfoxide, an anti-inflammatory), NSAIDS (Non-steroidal Anti-inflammatory Drugs - such as Phenylbutazone or bute) and corticosteriods injected directly into the joint.

Treatment options for horses with joint disease began to change some thirty years ago when scientists first attempted to replace some of the natural constituents of joint fluid and/or cartilage, in the hope that the body could use those building blocks to restore normal joint function. The first product used was Hyaluronan. Hyaluronan is a proteoglycan that's an important component of joint fluid and joint cartilage. Hyaluronan can be injected directly into the joint, and more recently, a new form of the drug can be injected systemically and find its way to the joint. Hyaluronan is thought to increase the viscosity of synovial fluid, inhibit some of the damaging enzymes and promote the synthesis of more sodium hyaluronate. Polysulfated Glycosaminoglycans (PGAG's) are another powerful class of drugs for the treatment of joint disease. Remember the GAG's are negatively charged molecules that bind and hold water. The water helps the articular cartilage manage the pressure of weight bearing.

These drugs have been shown to be anti-inflammatory and to increase the production of the proteoglycan component of cartilage. PGAG's can be injected directly into the joint and also into the muscle to achieve positive treatment results.

Oral Joint Supplements - Proposed Mode of Action

About ten to fifteen years ago, supplement manufacturers combined many of the materials found in healthy joints into an oral supplement. The thinking process was quite simple: put the building blocks for a sound joint in a bucket, feed it to the horse and let them absorb and utilize the materials to repair joint tissues. With this logic, treatment options went from intimidating needles to a "harmless scoop" of supplement.

The manufactures of "joint supplements" typically include a number of ingredients that may have beneficial results. The average joint supplement will contain ingredients from the following categories: nutrients, derivatives of nutrients and herbs.

In order for a joint supplement to achieve its desired effect in a living horse, several things need to happen. First, the substance must get absorbed across the gut. Second, if absorbed the substance must get to the joint. And finally if the substance gets to the joint, the body must utilize it for repair functions? Two of the most common ingredients included in joint supplements are chondrotin sulfate and glucosamine.

With respect to chondrotin sulfate, the absorption issue seems to be debatable due to the large molecular weight (size) of the compound. Chondrotin sulfate is typically obtained from bovine, whale and shark cartilage. Several studies have characterized the intact absorption as low; however, more studies are underway that will utilize digestive data from horses. IF chondrotin sulfate is absorbed, and IF chondrotin sulfate reaches the joint, what is the potential mode of action? As you remember, articular cartilage consists of water, collagen and proteoglycan. Chondrotin sulfate is the primary GAG that makes up the proteoglycans found in joint cartilage. It is known that joint injury and the ensuing inflammation cause a reduction in the amount of proteoglycan. Thus chondrotin sulfate theoretically could help replace proteoglycan.

Chondrotin sulfate has also been proposed to inhibit some of the degradative enzymes associated with cartilage breakdown, and to have general anti-inflammatory properties. Data to support the proposed actions of chondrotin sulfate in the test tube (in vitro) has shown positive results. Definitive data to document the effect of chondrotin sulfate in living horses is not available at the present time. Data in other animals models (humans, rats, dogs) can not be assumed to automatically hold true for horses. Thus the jury is still out with respect to chondrotin sulfate and its influence on joint health in horses.

Glucosamine is added to oral joint supplements either as hydrochloride or sulfate. As you would suspect, considerable debate exists as to the best form or glucosamine. Regardless of the exact chemical form, glucosamine is a significantly smaller molecule compared to chondrotin sulfate. By most estimates the absorption of glucosamine from the digestive tract does not seem to be a problem. However, specific horse absorption data has not been published in the scientific literature. IF glucosamine is absorbed, and IF glucosamine reaches the joint, what is the potential mode of action? Glucosamine is a precusor to the disaccharide unit of glycosaminoglycans (GAG), which comprise the proteoglycan found in articular cartilage. In vitro data supports the concept that glucosamine may stimulate synthesis of proteoglycan and collagen by chondrocytes. Experiments conducted in humans found glucosamine sulfate significantly more effective than placebo in improving pain and joint motion. Therefore, glucosamine may posses anti-inflammatory properties. Unfortunately, specific data in living horses are unavailable at the present time to definitively answer the questions surrounding the efficacy of glucosamine for joint health.

In addition to the chondrotin sulfate and glucosamine, supplement manufactures often include other ingredients necessary for synthesis of tissues for a healthy joint. Included on the list of possible joint supplement additives are: MSM (methylsulfonylmethane), copper, zinc, manganese and vitamin C. MSM is a source of sulfur that is necessary to strengthen collagen. The trace minerals copper, zinc and manganese are each involved as co-factors for synthetic processes of joint materials.

Finally, vitamin C is necessary for formation of collagen. It is not known if these additives have any special benefit in oral joint supplements beyond the benefit of simply providing the horse with a balanced diet.

The bottom line regarding the efficacy of oral joint supplements is unclear. Many good horsemen have used joint supplements on the horses in their care with glowing success. Others have tried supplements and reported no detectable difference in the way of going in their horses. Scientifically, many potentially promising benefits of oral supplements exist, but to date their efficacy in horses is unproven. Further, information on how much ingredient or which combination of ingredients is necessary to facilitate a joint response is totally absent. The unfortunate thing about the lack of definitive information is that many horse owners are considering themselves scientists and making their horses research subjects. The good news is that real research is going to eventually answer the questions.

The Potential Problem with Joint Supplements

Do oral joint supplements actually contain the amount of active ingredient indicated on the label? This is a huge problem since published analytical reports conclude that 84% of human over-the-counter glucosamine/chondrotin products do not meet label claim. Another study on oral chondroprotective products intended for animals indicated that 70% of products did not meet label claim. With regulatory agencies over run with new joint products, who is monitoring quality control of both ingredients and finished product? Further who is policing labels and advertisements for implied drug claims? Are studies being done that will answer concerns regarding safety of joint products? These are all fair questions with few answers. Supplement manufactures are beginning to appreciate the necessity of this information and have begun to organize themselves to answer consumer concerns.

About the Author

Dr. Steve Duren provides technical support and nutritional consulting for Kentucky Equine Research, one of the leading research institutions on equine nutrition. He is stationed in Idaho where he is responsible for KER's western and mid-western clientele. Dr. Duren received his Ph.D. degrees in equine nutrition from the University of Kentucky.
This information was presented at, and appears in the Proceedings of, the 2002 Alberta Horse Breeders and Owners Conference.

This information is maintained by of the Horse Industry Section of Alberta Agriculture in conjunction with Sylvia Schneider at Pondside Web Productions.

Stephen Duren, Ph.D
Kentucky Equine Research
Versailles, Kentucky