Omega-3s Significantly Improved Canine Arthritis in Double-blind Clinical Trial

Compared with mineral oil, fish oil supplementation for three months significantly improved objective measures of pain, lameness, and joint disease in dogs with osteoarthritis, according to a randomized, double-blind, multicenter trial.

The fish oil group also experienced significant increases in blood levels of omega-3 fatty acids, which preceded and correlated with clinical improvements, said Stephen Mehler, DVM, DACVS, of Hope Veterinary Specialists in Malvern, Penn. Fish oil supplementation appeared to be safe, although it was uncommonly associated with diarrhea that resolved with treatment, Dr. Mehler and his associates reported in the journal Prostaglandins, Leukotrienes and Essential Fatty Acids.

Fish oil contains high concentrations of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), which are omega-3 long-chain polyunsaturated fatty acids that partially displace arachidonic acid (ARA) from cell membranes. According to the researchers, although ARA is a component of pro-inflammatory molecules, such as leukotrienes and prostaglandins, EPA and DHA give rise to lesser inflammatory molecules that competitively inhibit ARA metabolism. Therefore, the net effect of fish oil supplementation “is a reduction in the anti-inflammatory environment systemically and within the joint.”

Supplementation with EPA and DHA can potentially improve rheumatoid arthritis and other inflammatory diseases. To assess its effects in canine osteoarthritis, the researchers randomized 74 purebred and mixed-breed dogs aged two to 14 years, with radiographically confirmed osteoarthritis of the stifle or coxofemoral joint, to receive either medical grade mineral oil (placebo) or fish oil at an EPA:DHA ratio of 3:2. The supplement was dosed at 69 mg per kilogram of body weight per day. The study excluded dogs that could not stop NSAIDs, were already receiving omega-3 supplements, or had surgical joint conditions, such as cruciate ligament instability, grade two medial or lateral patella luxation, or hip luxation.

By day 42 of the trial, crepitus, pain, and joint effusion had improved by about 50% in dogs receiving fish oil, while remaining essentially unchanged in dogs receiving placebo (P <.0001). The fish oil group also improved markedly by day 42 on a visual analogue scale of overall clinical improvement, while the placebo group remained comparable to baseline (P<.0001). For both measures, treatment-associated improvements persisted at day 84, while the placebo group resembled baseline.

Lameness and discomfort in the fish oil group showed a trend toward improvement by day 42, but did not improve significantly compared with placebo-treated dogs until day 84. On a 10-point scale, lameness improved from a median of grade 4 (baseline) to grade 1 (day 84) in dogs receiving fish oil, while remaining at about grade 4 to 5 in the placebo group, throughout the trial (P<.0001). Likewise, in the treatment group, discomfort improved from more than 5 to less than 1 on a 12-point visual analogue scale, while showing no overall trend in the placebo group (P<.0001). The researchers noted that lameness and discomfort might have taken longer to improve than other measures since they are aggravated by chronic compensatory mechanisms, nerve stimulation, and muscle atrophy, all of which take relatively longer to resolve.

Tests of red blood cell membranes showed that ratios of circulating ARA to circulating EPA and DHA were comparable between the study arms at baseline, were significantly lower (P < .0001) in the treatment group at day 42, and remained significantly lower in the treatment group at day 84. There were no serious adverse effects in either study arm; however, four dogs (two per group) developed diarrhea that resolved after a few days of metronidazole therapy, and two dogs in the placebo group dropped out of the trial in order to receive rescue analgesia.

“The clinical significance of the statistical findings was readily apparent,” the researchers concluded. “Patients receiving daily supplementation of fish oil had consistent clinical improvements in their pain, dysfunction, and overall well-being by the conclusion of the trial.” Future studies should assess the longer-term effects of this particular 3:2 EPA:DHA supplement, potentially in comparison with NSAIDs or other forms of EPA and DHA.

The study was partially funded by Veterinarian Recommended Solutions, and laboratory analyses were performed by OmegaQuant Analytics. Dr. Mehler reported compensation from VRS for serving on its scientific advisory board. One coinvestigator is an owner of OmegaQuant Analytics.

Dr. Amy Karon earned her doctorate in veterinary medicine and master’s degrees in public health and journalism from the University of Wisconsin-Madison. She was an infectious disease epidemiologist and “disease detective” (EIS officer) with the Centers for Disease Control and Prevention before becoming a full-time medical writer. She lives in the San Francisco Bay area, where she volunteers for the local Humane Society.