After taking a closer look at chondroitin last week, it is now the turn of another joint supplement ingredient, hyaluronic acid.
Hyaluronic acid (HA) is a natural constituent of connective tissue, cartilage and joint fluid, and is made up of glucuronic acid and N-acetylglucosamine. It has viscoelastic properties that help to lubricate the joint, reduce friction and aid energy dissipation. Hyaluronic acid (or hyaluronate) is injected into joints as well as given orally in supplements. The theory behind injecting it into joint spaces is that it boosts lubrication, thus reducing friction; reduces inflammatory mediators and improves nutrition to the joint cartilage.
Hyaluronic acid was first injected into horse’s joints, and a research paper describing the treatment appeared in a veterinary journal back in 1970. After positive effects were found, it was extended to human use. It is injected as a therapy for jaw (temporomandibular) joint (TMJ) and knee joint osteoarthritis in humans. Researchers have assessed it as ‘as useful as corticosteroid injection for pain relief’ when used for TMJ osteoarthritis. Reviewers criticised the quality of the research studies, however, and further good quality research is necessary to determine its clinical usefulness and understand exactly how it works.
Whether or not HA can even be absorbed after oral dosing is questionable, and researchers in China have tried combining it with phospholipids to try and enhance absorption, with some success. Other researchers have proposed that it might act via release of its glucosamine component or that it might switch on receptors in the gut and have activity without being absorbed at all.
There is no good quality evidence published for orally supplemented HA in humans or any other species. One study of oral HA from chicken combs (which also included collagen and other polysaccharides) and one of oral HA along with quadriceps strengthening exercise in humans with knee osteoarthritis showed reductions in pain and stiffness, but not significantly greater than from the placebo.
HA is made from animal or bird by-products including chicken combs (a rich source) and mammalian umbilical cords so if you wish to feed your horse a vegetarian diet, then HA is not an option. HA is an expensive ingredient, so very small amounts are commonly used in horse supplements, questioning whether or not there will be any therapeutic effect at all.
In the future, if oral HA is available in an affordable form that can be absorbed and reach the joints, it might well have some therapeutic benefit for the horse. Until further evidence is available, however, there is little point in paying extra for HA in joint supplements, and your money is probably better spent on higher – more effective – doses of the more reliable ingredient glucosamine.