Two Studies of Fish Oil for Canine Arthritis

One of the most popular nutritional supplements these days is fish oil. It contains a high proportion of omega 3 fatty acids (EFA), notable eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). This supplement is purported to have a broad range of beneficial effects in many disease conditions due to its effect on chemicals in the body involved in the inflammatory response (for more details see this article on eicosanoids). Some of these effects, such as a reduction in the rate of heart attacks in people with established heart disease and heart attack risk factors, are well-supported by research data. Other claims are less clearly valid. Several literature summaries are available from the Agency for Healthcare Research and Quality, and Medline.

In the veterinary arena, EFA supplements are widely used for allergic skin disease, with modest supportive clinical trial evidence (see also 1, 2, 3, 4).  In humans, there is limited evidence to support an effect on some clinical variables in patients with rheumatoid arthritis, and some have suggested osteoarthritis treatment as a veterinary application for these supplements. There is reasonable biologic plausibility to support investigating this use of EFA supplements, and two articles in a recent issue of the Journal of the American Veterinary Medical Association (JAVMA) report studies evaluating the use of fish oil supplements for dogs with confirmed osteoarthritis. I shall briefly review each of them.

The first study [1] was a multicenter, randomized, double-blind, placebo-controlled prospective study lasting 24 weeks. 167 dogs were randomized into two groups, one receiving a diet supplemented with EPA and DHA, the other receiving a pretty closely-matched control diet. There were no significant differences in any relevant variables between the groups at baseline. 23% of the dogs failed to complete the study (9% in the treatment group and 14% in the control group), and there were no significant differences between the groups with respect to these dropouts.

Assessment measures were subjective, with an owner survey and a clinical assessment by participating veterinarians. Dogs were evaluated at 6, 12, and 24 weeks after beginning the diets. Bloodwork showed significant increases in the blood levels of EHA and DHA in the dogs fed the test diet, so these substances were clearly absorbed. The owner survey evaluated 13 measures of comfort and function over three time periods (0-6 weeks, 6-12 weeks, and 12-24 weeks on the diets). Of these, 2 measures were significantly different between the groups at the first evaluation, and 1 measure was different at the last evaluation. There were no significant differences between the groups in clinical evaluation by veterinarians.

The study was apparently well-designed and well-conducted. The measures of outcome were subjective, which is less than ideal. It seems fairly clear that the results do not support the use of EFA supplementation for osteoarthritis. After all, out of 39 possible points at which the groups were compared in terms of owner evaluation only 3 showed changes not attributable to chance, and none of the evaluations by veterinarians showed significant difference. Unfortunately, the discussion section of the article is less an objective survey of the trial or the overall preponderance of the evidence than it is an attempt to put the most positive possible spin on the results.

The authors suggest their subjective measurement instrument may not have been sufficiently sensitive to detect a change and try to attribute the failure of the veterinarians to detect a difference to the hospital environment and limitations on clinical evaluation. They then conclude, “Our results suggest an ameliorative effect of omega-3 fatty acid supplementation in arthritic dogs,” and “ingestion of the test food….appeared to improve the arthritic condition in pet dogs with osteoarthritis.” Such a conclusion so clearly  at odds with the data presented in the report seems to be more an example of confirmation bias and cognitive dissonance than a reliable presentation of the evidence.

The second study [2] was conducted by several of the same authors. It too was a well-designed randomized, double-blinded, placebo-controlled, prospective study of the effects of dietary EFA supplementation on dogs with osteoarthritis. 44 dogs were enrolled in the study, and 14% failed to complete it (9% in the treatment group and 5% in the control group). Again there were no significant differences detected at baseline and no differences with respect to dogs that failed to finish the study. Both subjective and objective measures were evaluated at baseline and after 45 and then 90 days of the diets. Owner and clinician subjective evaluations were compared as were the results of force plate gait analysis.

In contrast to the previous study, there were no significant differences in owner evaluations of the subjects’ comfort and function. The authors attributed this to the low number of subjects rather than the more parsimonious explanation that there was no differences of sufficient magnitude to be noted. The clinician evaluations at 90 days showed significant differences from baseline for the test group in 3 of 5 measures. However, there were no significant differences between the test and control group for any measure.

The authors stated, correctly in my opinion, that “subjective assessment of limb function lacks repeatability as an outcome measure and is inferior to objective data obtained from force platform gait analysis.” Such an analysis was performed on all subjects. The results showed no change from baseline to 90 days for any of six variables measured (peak vertical force, vertical impulse, braking and propulsive peak forces, and braking and propulsive impulses). The test group did show a statistically significant difference in the mean percentage change in one measure, peak vertical force.

Again, these results provide lackluster support for the contention that EFA supplementation may be beneficial for dogs with osteoarthritis. Some subjective clinical measures showed a difference, but this is not consistent with the results of the other, larger trial, and the authors themselves minimized the significance of these results in both papers. One objective measure did show a statistically significant, and likely clinically significant change. However, the combined results of the two trials offer tepid support for the hypothesis under examination, and an interpretation of no meaningful effect seems much better supported by the results.

Unfortunately, the authors again spin these results in the most positive way possible:

“Together with the findings of our other study, findings of the study reported here supported the hypothesis that ingestion of fish oil omega-3 fatty acids improves clinical signs in dogs with osteoarthritis….Dietary supplementation with fish oil omega-3 fatty acids resulted in an improvement in weight bearing in dogs with osteoarthritis.”

The authors do acknowledge some of the limitations of their study and suggest that further research is necessary for definitive recommendations. I would agree that these results might justify further study, though I see no reason to expect dramatic findings of benefit. However, the reality is that in the world of veterinary medicine, with limited resources and clinical trial evidence, the more likely outcome of these reports is going to be an increase in the prescription for EFA supplements intended to treat osteoarthritis. The positive statements in the abstracts and discussion sections are likely to be the “take-home” message many readers get from the reports, despite the reality that the data is considerably less positive. I always appreciate well-designed and conducted research, but these reports emphasize the difficulty in conducting such trials without having an investment in their outcome that affects the interpretation of the results. This is a large part of why careful and critical evaluation of the primary literature for oneself is such a key component to sound, evidence-based practice.

References

1. Roush JK, Dodd CE, Fritsch DA, Allen TA, Jewell DE, et al. Multicenter veterinary practice assessment of the effects of omega-3 fatty acids on osteoarthritis in dogs. J Am Vet Med Assoc. 2010 Jan 1;236(1):59-66.

2. Roush JK, Cross AR, Renberg WC, Dodd CE, Sixby KA,, et al. Evaluation of the effects of dietary supplementation with fish oil omega-3 fatty acids on weight bearing in dogs with osteoarthritis. J Am Vet Med Assoc. 2010 Jan 1;236(1):63-73.

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18 Responses to Two Studies of Fish Oil for Canine Arthritis

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  2. PamSB says:

    Thank you for this review. As the owner of a dog with arthritis, this review will prove useful if my vet suggests this treatment option. I’ve already resisted the suggestion to try acupuncture.

    BTW, the page numbers on the second citation should be 67-73.

  3. skeptvet says:

    Thanks for the comment, and the erratum!. I copied the page numbers off Pubmed, as easier then typing them in, but I have made the correction.

  4. Rita says:

    The fish will welcome your report, too – ah humans! always trading the out-group’s interest for the in-group’s.

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  6. Bonnie says:

    Thank you for this. I just got back from the vet, who just “prescribed” this for my dog’s arthritis. This was my 2nd visit and I was hoping for a more substantial treatment. I didn’t want to be argumentative, but after reconsidering I asked her if there were studies looking into the efficacy of this. After a long pause, she said something like the surgeon has seen good results with it – anecdotal. I wasn’t sure if it had been studied in dogs, and found this post before hitting pubmed. I appreciate your saving me the time of combing through the data. Looks like it’s trip #3….

  7. Andrew at arthritis in dogs says:

    As a specialist veterinary orthopaedic surgeon in the UK, I would agree with the thrust of this post, which is that there is very minimal or no evidence that these supplements are beneficial for dogs with arthritis. I have had a few owners who thought they may have helped, but even this highly anecdotal evidence was fairly half-hearted. I’m open-minded and willing to consider alternative or complementary therapies- but the fish oil data is extremely underwhelming and I won’t be recommending it any time soon. Thanks for this interesting post.

  8. Beka says:

    Thank you for the analysis of these studies I found it informative in terms of the studies but not the mechanism in which these studies were based on. There is reason why doctors recommend Omega 3 supplementation in canines with OA and it is often based on the production of Eicosoniods and the Omega 3 role in lowering the level of harmful prostaglandins and leukotrienes formed. While I believe in at least one of these studies (i have not read the weight bearing study) the author never should have accepted there alternative hypothesis, I do believe at least mechanistically Omega 3s have a role in reducing the inflammatory response in dogs with OA. However, i must say that my evidence is based off of purely subjective findings. While i appreciate your candor and your logic I do believe that there is not sufficient evidence as of yet to either support or refute the hypothesis that dogs with OA could benefit from Omega 3 supplementation. As far as Omega 3s go in general they do much more then help the treatment of OA in canines which is why i will continue to recommend them as a possible supplement for owners to consider. There is also a study that shows that when Omega 3 is used in conjunction with Carprofen it lowers the lowest effective dose thereby saving the owner some money. I realize my analysis of your interpretation is not by any means extensive and while I may disagree with your discounting of Omega 3s as a possible supplement for OA I do agree with your analysis of these papers (despite its at times questionable objectiveness when analyzing the discussions). Being a skeptic is hard and i appreciate what you do and now after finding your blog i will be happy to continue reading. I just ask that you be a bit more careful about drawing absolute conclusions from two papers written by the same author. I know you mean well i just like to see people fully informed about all the mechanisms and studies out there. I would love to see you develop this section a bit further including the mechanisms of Omega 3 and why it may be recommended, as well as other studies done to assess it’s efficacy.

  9. skeptvet says:

    I appreciate your feedback, but I think you are chastising me for a position I have not taken. My conclusion was not an “absolute” one nor did I discount the possibility of an effect. Here is what I said in my review of this intervention:

    Essential fatty acids from fish, including EPA and DHA, have many potential benefits based on sound theoretical and in vitro work showing their potential to reduce inflammation. There have been very few studies in companion animals on their usefulness for arthritis, and these do not seem to show much if any benefit, though the work is preliminary. The research in humans is also variable in quality and in results. Fish oils are very likely safe for most pets, and they may or may not have any beneficial effects on arthritis, but the data so far is not encouraging.

    I agree that there is a plausible theoretical mechanism for a posisble benefit, I simply don’t believe these studies demonstrated an actual meaningful clinical benefit. I even agreed with the study authors that further research is warranted. But it is important for people to understand that most extrapolations from fundamental principles turn out not to work in clinical practice, so just because something might work isn’t proof that it does. Hopefully, further research will find real benefits, because I would love to have yet another tool for dealing with arthritis. But so far, the data are not encouraging.

  10. csl says:

    Without reading the original journal articles it really sounds like EFAs are not that helpful. However, I have been feeding my dog with arthritis fish oil for over a year and have seen noticeable differences in mobility. In fact, when I have switched to a cheaper oil my dog started to limp on an almost daily basis but when I switched back to a high quality oil he stopped limping again. During the time he was fed the fish oil he also received monthly Adequan shots. But since the Adequan dosage, his diet, and his exercise were constant during that time period any changes in mobility would have been due to the fish oil.

  11. skeptvet says:

    Well, I think the jury is still out on fish oils. The studies showed some evidence of benefit, but this was weak and inconsistent. So far, I don’t think the answer is clear either way.

    As for individual experiences like yours, unfortunately they can easily fool us. Just last week I wrote about how almost half of owners and vets see an improvement in arthritis pain and in function in clinical studies when the dogs aren’t actually getting any treatment. So lots of things might be explaining the improvement you’re seeing besides the fish oils.

  12. Van Thein says:

    Fish oil for my old dog is not a cure but for 2 weeks it’s all he’s taking for arthritis pain. Carprofen was the drug of choice prior to this. Taking only fish oil (3000 units) daily he can still walk without obvious pain, although not 3 times per day. Last year prior to using fish oil he could not walk 100 yards if he did not have Carprofen in his system. It’s the only evidence I have that fish oil may have some benefits for him. His Xrays show very serious arthritis of the hips. I hope he can go back on Carprofen but am thankful that fish oil helps him a little.
    I wish Adequan were studied more.

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  14. Sandy says:

    I’ll take anecdotal evidence, as my Aussies are a couple of exemplary anecdotes. The senior Aussie (14 years old) is playing much more, even jumping on and off of the couch to chase toys, and is just plain old perkier, which happened some time after the addition of the fish oil. My pup (7 months old) developed dry skin after his move with me to Arizona, and so the vet said I could put him on it too, and he no longer has any evidence of dry skin (after a couple of weeks).

  15. Beth says:

    There’s a 2012 review article on supplements for osteoarthritis at http://onlinelibrary.wiley.com/doi/10.1111/j.1939-1676.2012.00901.x/epdf
    They write
    ” Twenty-two papers were selected and reviewed, with 5 studies performed in horses, 16 in dogs, and 1 in cats. The strength of evidence was low for all nutraceuticals except for omega-3 fatty acid in dogs. There were limited numbers of rigorous randomized controlled trials and of participants in clinical trials.”
    They reviewed 4 studies of an omega-3 supplemented diet in dogs.

  16. Adam says:

    Really interesting discussion that crosses into both my professional life and my home life looking after a dog with joint problems. I would be interested in your thoughts on a fundamental issue supplements come up against in terms of producing peer reviewed evidence. If a product is used in a double blinded placebo controlled study, and the animals have been diagnosed with a disease (in this case OA) and the effects are demonstrated objectively (force plate, accelerometer or something similar) this constitutes medicinal effect (as opposed to ‘stiff’ dogs, or non controlled subjective trials that would not constitute ‘medicinal’). As supplements are regulated by the VMD as non-medicinal products a peer reviewed study would not allow the company to refer to their product having been used or even steer people in the direction of a study that may have taken place through someone else. I do not disagree that many claims are made on very weak science, but could this be driven by the fact sound science is being hindered through this type of regulation?

  17. skeptvet says:

    Well, I can’t speak to the regulatory environment in t he UK.In the US, unfortunately, the government is effectively prevented from regulating supplements. There is no requirement for proof of safety and efficacy so long as no direct claims to treat a disease are made (and even this rule is routinely violated with no consequences in most cases). The burden is on regulators to identify harmful products and remove them from the market, and the burden is so high only one supplement has ever been banned under the law. So in our case, the absence of evidence is due entirely to the fact that there is no requirement to produce any, and few companies are willing to pay for studies that aren’t required.

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