Critical review of research evaluating glucosamine-based nutraceuticals for treatment of joint pain and degenerative joint disease in horses

It was more than 25 years ago that two German researchers quietly associated supplementation of glucosamine to horses with improvement of joint disease. In the 25 years since, glucosamine and its related chemical chondroitin have become the most extensively used non-allopathic treatment for articular inflammation and arthritis in horses. While the practice of supplementing arthritic horses with these products has, in earlier times, been considered a complete unknown in terms of safety and efficacy, the story is quite different today. An expanding body of knowledge on glucosamine continues to raise scientific curiosity about the general principles and cellular basis of treating equine osteoarthritis and inflammation with glucosamine-based nutraceuticals. This review critically interprets the published in vivo studies designed to investigate glucosamine-based nutraceuticals for horses with joint pain and/or inflammation. These studies have contributed valuable preliminary information as to the possible usefulness of glucosamine-based nutraceuticals in horses, and demonstrate an encouraging trend to manufacturers of these products investing in research. Importantly, however, these studies have significant limitations that until now have not previously been addressed. For example, measures of bioavailability in horses have not acknowledged fundamental binding of glucosamine to serum proteins and as such likely provide gross underestimates. Other more general limitations include underpowered studies, unbalanced research design, non-existent or inappropriate controls, unclear or non-representative experimental conditions and uncharacterized or complex, heterogeneous experimental materials. Shortcomings such as these have heavily influenced interpretation, as well as misinterpretation, of results. Because of these substantial limitations, the existing data on glucosamine-based nutraceuticals for horses cannot be considered conclusive evidence supporting the efficacy of glucosamine-based nutraceutical products. Recommendations are made as to minimum scientific requirements for future research into glucosamine-based nutraceuticals for horses.