I am often asked by clients or readers about specific products, and while I certainly can only investigate a small proportion of all the stuff marketed to pet owners, I try to look at as many of these things as I can. Some of my colleagues have begun using a product called HealthyMouth , a water additive reported to reduce accumulation of plaque and retard the development of dental disease. This product has received a seal of acceptance from the Veterinary Oral health Council (VOHC) and an endorsement from Dr. Fraser Hale, a dental specialist and someone who generally takes a skeptical, evidence-based approach to dental therapies. Dr. Fraser has gone from being skeptical of the product to actively recommending and distributing it. These are sources I believe are trustworthy, so I thought I ought to take a closer look at the product. In keeping with my general approach, I will review the product in terms of the following general issue:
1. Basic plausibility for proposed effect/mechanism of action
2. Pre-clinical, non-target species research
3. Clinical trials
4. Marketing claims
The product ingredients list is extensive, though specific quantities/concentrations are not provided. Only two are described as “active” ingredients, papain and zinc gluconate, but I will discuss several others that appear to be included for some specific effect. Theoretical rationales are provided for some ingredients but not others. Many ingredients are described as “organic,” which I suspect has little relevance. The dog and cat products appear from the ingredient list to be identical except for the addition of the amino acid taurine to the feline product.
1. Pomegranate- No specific claim is made about this ingredient.
There are a few in vitro trials that suggest anti-bacterial effects from pomegranate juice. There are also a number of human clinical trials suggesting anti-plaque and anti-bacterial effects for oral rinses containing this ingredient (1,2). There appear to be no clinical trials in dogs other than the two unpublished studies conducted by HealthyMouth, and no trials at all in cats. Clinical trials in humans and lab animal studies show little risk, though allergic reactions in humans have been reported, and there are some concerns about possible interference with the metabolism of other supplements or drugs.
2. Yucca- I was not able to find any in vitro research suggesting a benefit for yucca extract in preventing or treating dental disease. There have been a couple clinical trials of one yucca extract in dogs (3) and one in cats (4) reporting some decrease in the odor of flatulence, and no significant adverse effects were reported. There are reports of yucca extracts causing gastrointestinal symptoms. I was not able to find any clinical trials of yucca extract as a preventative or therapeutic for dental disease in humans or in dogs or cats.
3. Zinc gluconate- The claim made for this ingredient is that ” zinc gluconate operates as an antibacterial agent.” There are clinical trials of zinc gluconate containing rinses and toothpastes in humans which appear to show decreased plaque and gingivitis, but the compound is almost always combined with triclosan or other antibacterials, so it is unclear what role the zinc itself has in any effect seen. There are no clinical trials investigating the use of this agent in preventing or treating dental disease in dogs or cats. Excessive zinc ingestion can cause serious and even life-threatening complications.
4. Blueberry- I found one study suggesting a particular blueberry extract might have a weak effect reducing the aggregation of bacteria found in the human mouth (5). There appears to be no lab animal, or clinical trial evidence in humans or other animals that blueberry is useful in the prevention or treatment of dental disease. Blueberry’s are reported to contain substances which have anti-oxidant properties, but the clinical significance of this is unclear, and no apparent connection exists to prevention of dental disease.
5. Papain- A combination of proteolytic enzymes found in papaya, papain does not appear to have been studied extensively as an agent for prevention and treatment of dental disease, though it is occasionally found in toothpastes. I was not able to find any clinical trials in humans, or in dogs or cats regarding dental disease. There are some safety concerns as large amounts have been reported to cause perforation of the esophagus in humans, allergic reactions are possible, and there is some potential risk of reducing blood clotting function, especially in combination with some other herbal ingredients including cloves which is one of the flavoring agents in HealthyMouth.
6. Vitamins B2 and C- These appear to be included as “anti-oxidants” and to “increase the immune response.” The notion of boosting the immune system is a meaningless marketing device and while there is some preliminary suggestion that preventing oxidative damage can sometimes be a good thing, oxidation is also one of the ways the body suppresses cancer and fights infection, so it is not appropriate to assume that reducing it, even if these substances actually do that in a living animal, is a good thing.
7. Clove and cinnamon- These are apparently added as flavoring agents, and I found no research to suggest benefit or risk associated with them in dogs and cats. I wouldn’t expect them to be especially appealing to cats, but the company claims they love it.
As I mentioned, HealthyMouth has been awarded the Veterinary Oral Health Council (VOHC) seal of acceptance. VOHC is an independent organization that reviews the evidence for products claimed to have value for prevention and treatment of dental disease in animals. The organization requires clinical trial evidence to support product claims, and they have pretty specific protocols to ensure these claims are adequately demonstrated. However, I still have some concerns about the trials HealthyMouth uses to support its product claims.
As I often point out, all of us have biases about the ideas and beliefs we hold. We naturally believe our hypotheses to be true, and this can lead us to see what we want or expect to see, to focus on confirming information and ignore or minimize contrary information (e.g. confirmation bias and cognitive dissonance). And non-ideological motives, such as financial incentives, can also influence our interpretation of what we see even if our intentions are quite honest. It is well established in human medicine that trials funded by industry, for example, tend to have findings favorable to the products of the funder. The purpose of formal clinical trials is to help us test our ideas in a way that hopefully prevents these biases from inappropriately influences our findings.
It is important to be aware of the potential biases involved in a clinical study, not because this information allows us to automatically dismiss the findings but because it helps us spot weaknesses in the methods and evaluate the results in context.
In the case of HealthyMouth, the two clinical studies in dogs were both funded by the company that manufactures the product. And thought the chief investigator, Dr. Jean Dodds, is a well-respected veterinarian who has done much fine work for the veterinary profession and animal welfare, she is also a prominent advocate of “holistic” veterinary medicine, having even received the Holistic Veterinarian of the Year award from the American Holistic Veterinary Medical Association, an organization I’ve discussed frequently before. These facts are relevant because they indicate the high potential for a bias favorable to the product in these trials, and so we must look carefully at the methodology of the trials to see if there are adequate controls.
It is difficult to evaluate all the details of the methodology since the trials have not, as far as I can tell, been through peer review or been published in the scientific literature. The information I evaluated about them comes from the HealthyMouth web site. It appears that two trials, with 40 different dogs in each study and a duration of 28 days (requirements of the VOHC protocol) were conducted by Dr. Dodds in a greyhound dog rescue center and blood bank she founded and manages. The advantage to this, apart from logistics, is that the husbandry of the dogs was likely pretty uniform, which reduces sources of variation between groups. The disadvantage is that the dogs were all of one breed (and one in which dental disease is a particular problem), and the conditions were likely very different from those experienced by typical pet dogs.
The VOHC standards recommends randomization of subjects, but it does not appear that procedure was used in this study. Subjects were allocated to groups based on kennel housing so that the access to treated or untreated drinking water could be more easily controlled. This introduces some small potential source of difference between groups other than the treatment itself.
The dogs had a full dental cleaning under anesthesia at the start of the trials, and their plaque scores measured at intervals, as recommended in the VPHC protocol. A big concern about the study, however, is that there was apparently no blinding. The treated and untreated water were easily distinguished, and the staff managing the dogs and evaluating their oral health were apparently aware of which group they were in. This always introduces a strong potential for bias, and it is especially a concern in a trial like this where there is a strong presumption of safety and efficacy in advance on the part of the organizers of the trial (the company making the product) and possibly among the investigator and her staff. In any case, the evidentiary value of a clinical trial is substantially lower if it is not properly and effectively blinded, and such trials almost always find a positive treatment effect.
In any case, the trials both showed a strong positive effect on plaque scores. No trials have yet been made public in cats, and no independent evaluation of HealthyMouth appears to have been done.
As is probably inevitable, the marketing of this product involves a lot of “satisfied customer” testimonials. Stories of dogs and cats who apparently experienced great benefits are told, and of course no stories from pet owners who do not believe their pets befitted are told. This creates the impression of a safe and effective product, but of course it is a form of advertising, not a reliable source of information about whether the product actually works.
Dr. Hale gives the company founder credit, appropriately in my opinion, for marketing HealthyMouth as an adjunct to appropriate home and professional dental care, not a magic cure-all or substitute for other, established preventative and treatment methods. This is a point in the company’s favor.
Not so encouraging is the frequent use of words like “natural” and “artificial” to imply that the product must be safe. The advertising even goes so far as to claim there are “no chemicals” in the product, which is nonsense since water, blueberry juice, and every other ingredient is a “chemical.”
As I have often pointed out, botulism and uranium are “natural” and polio vaccine and penicillin are “artificial,” so these words don’t really mean what they are implied to mean. In any case, several of the ingredients have recognized health risks in humans, and most have not apparently been tested for safety in dogs or cats. And it is impossible to tell from the web site how much of the various ingredients are in the product, so no definitive statements about safety can be made. I would be surprised if there are any significant risks from the product since it would require an awful lot of most of the ingredients to be dangerous as far as I can tell, so I’m not especially worried about the safety issue. But the claims of safety are really assumptions based on the naturalistic fallacy, and supposedly safe herbal and homeopathic remedies have turned out to be harmful in the past (e.g. cinnamon bark and homeopathic belladonna), so at least a little caution is appropriate.
There are some very limited in vitro and human clinical data to suggest it is plausible that the ingredients in this product might have some benefit in preventing dental disease. The only research actually testing the product in a veterinary species (dogs) showed benefits, but some caution is warranted in interpreting these results because they are unpublished, industry-funded trials with a lack of robust methodological controls for bias and other non-treatment effects. There is no significant evidence of any real risk from the product, though it doesn’t appear that most of the ingredients, alone or in combination, have been tested for safety in cats and dogs. The company generally markets the product in a responsible way, though it does make use of some misleading advertising strategies such as promotion through testimonials and invocation of the naturalistic fallacy.
Overall, I am inclined neither to recommend the product nor to recommend against it. I applaud the company for taking the first steps in conducting the research necessary to obtain VOHC approval, and I hope additional research, ideally independent and better designed, is eventually carried out to further clarify whether this product has real safety and meaningful efficacy. I agree wholeheartedly with the company that dental disease is a serious condition and that most pets do not receive adequate preventative care or treatment, so I hope additional research does eventually show this product to be a useful adjunct to other oral care practices, but I think it the case has not yet been effectively made.