Nutraceuticals: joint supplements, fish oils, and others (Proceedings)
"What evidence-based joint supplement, fish oil and probiotic recommendations can be made?"
For joint supplements, the news isn't good. Despite the enthusiasm, and aggressive marketing, not only is compelling evidence for efficacy lacking, there is evidence against efficacy. For example, a recent study in humans1 concluded that, "Glucosamine and chondroitin sulfate alone or in combination did not reduce pain effectively in the overall group of patients with osteoarthritis of the knee. Exploratory analyses suggest that the combination of glucosamine and chondroitin sulfate may be effective in the subgroup of patients with moderate-to-severe knee pain." This study is available free online for anyone to read and draw one's own conclusions. In veterinary medicine, a recent systematic review of clinical treatments for osteoarthritis in dogs2 concluded that, "A high level of comfort exists for meloxicam that the claimed relationship is scientifically valid and that its use is clinically efficacious for the treatment of osteoarthritis in dogs. A moderate level of comfort exists for carprofen; etodolac; pentosan polysulphate; green-lipped mussels; P54FP; polysulfated glycosaminoglycans; and a combination of chondroitin sulfate, glucosamine hydrochloride, and manganese ascorbate. An extremely low level of comfort exists for hyaluronan." A subsequent (manufacturer-funded) controlled trial3 of pentosan polysulphate (PPS) optimistically concluded that, "PPS administered after stabilization of the cruciate deficient stifle may prove to be a useful adjunctive treatment option, although further studies are necessary to substantiate this claim." – particularly given the result that, "All dogs clinically improved after surgery without differences in lameness score, vertical GRFs, or radiographic progression."
With regard to fish oil, concerns remain for the quality of dietary supplements. Although clients and veterinarians may not be aware of the situation, the contents of dietary supplements are not currently regulated, and can vary widely depending on the manufacturer' standards. Moreover, governmental regulation, oversight, and quality-assurance processes for prescriptions are quite different from those for dietary supplements. Safe preparation, packing, and holding of human dietary supplements is governed by the FDA's "Good Manufacturing Practices" (GMPs). The GMPs applicable to dietary supplements are those used for foods, however, not for drugs. The FDA recently established revised GMP regulations that require dietary supplement manufacturers ". . . to evaluate the identity, purity, strength, and composition of their dietary supplements." Mandatory compliance with these regulations will take effect between June 2008 and June 2010. Veterinarians interested in using fish oils could look for products that are GMP-certified and can demonstrate that they have been stripped of heavy metals, dioxins and halogenated polycarbons.4Even in this case, the evidence for efficacy for fish oils is limited to a pure formulation called P-OM3 (Lovaza), and marketed as a drug. I this been shown to be effective for treating hypertriglyceridemia in humans at a dose of 4 grams/per day (or about 60 mg/kg body weight for an adult human). Amounts of omega-3 fatty acids in dietary supplements often are much lower. Additionally, a recent study has called the specificity of the effects of fish oil on coronary heart disease risk in humans into question. Cundiff, et al., recently suggested that data supporting the benefits of fish or long-chain omega-3 fatty acid (FA) supplement consumption and coronary heart disease may be confounded by other dietary and lifestyle factors. Using the Diabetic Control and Complications Trial (DCCT) database (n= 1,441), correlations between consumption of omega-3 FAs and saturated FAs to dietary variables (energy, macronutrients, sodium, and cholesterol) and to age, gender, exercise level, and tobacco use were tested. They found that omega-3 FA intake was inversely correlated with consumption of calories, percent calories from total fat, and percent calories from saturated FAs, and directly with dietary fiber intake - a nutrient intake profile associated with a lower CHD risk. Moreover, the higher saturated FA intake associated with not eating fish is itself associated with less exercise and more tobacco use. They concluded that their findings provided evidence that associations observed in studies suggesting a benefit of fish or omega-3 FAs may be due to a convergence of greater fish intakes with an overall healthier dietary pattern rather than with a specific effect of these FAs. Such confounders have not been considered in veterinary medicine to my knowledge.
The evidence for effectiveness for probiotics in dogs and cats also is weak. Probiotics are live microorganisms that, when administered in adequate amounts, confer a health benefit on the host. These are a subset of so-called "alimentary pharmabiotics" which are defined as any material with (documented) health benefit that can be mined from host-microbe-dietary interactions in the gut. In addition to live whole organisms (probiotics), alimentary pharmabiotics also include other components of commensal microbiota, including dead organisms, cell proteins, cell wall polysaccharides, probiotic DNA or GMOs that have beneficial effects on the host.