Tuesday, January 13, 2009

Mouthwash: Friend or Foe?

There is something about that tingling, burning sensation of Listerine that always keeps me coming back. I just don't "feel" like that other stuff is working. However, according to a recent study published in the Dental Journal of Australia using mouthwash containing large amounts of alcohol is associated with greater risk for developing oral cancer.

A possible link between mouthwash use and oral cancer was brought to my attention while riding the T Tuesday morning by Metro. I did a quick PubMed search and found several articles -- even REVIEW articles -- on the issue that date back to 1991. This is not a new idea, however this finding is quite controversial. I decided to review 3 articles on the subject (I was limited by those journals subscribed to by HSPH at this point).

 The first article, a 1996 review in the American Journal of Epidemiology, proposed a spurious (non-causal) association between mouthwash use and oropharyngeal cancer. The authors (one of whom worked for Procter and Gamble; the work was sponsored by a Pfizer company) argued that alcohol and tobacco use likely accounted for the association between mouthwash use and oral cancer. For example, consider that smokers are more likely than nonsmokers to use mouthwash to eliminate their bad breath, and that smoking is strongly associated with oral cancer -- it is. While it may seem that mouthwash was linked to cancer, really it may have just been the tobacco use.

In 2003, an article was written and published in the Journal of the American Dental Association (this study was also financially supported by a Pfizer company) to review the literature examining the mouthwash-oral cancer relationship. Nine studies were considered - six showed no association between mouthwash use and oral cancer, and three showed a positive association. In addition, this article re-analyzed data from a large population-based National Cancer Institute study with nearly 1500 cases and a similar number of controls. The re-analysis showed that mouthwash had the same moderate effect on both "true"/mucosal and "pseudo"/nonmucosal cases of oral cancer; whereas other known risk factors (alcohol and tobacco use) for mucosal type oral cancer were quite strongly and predictably related to "true" cases, but not to the "pseudo" cases.  Of course, confidence intervals are not presented.

These two studies with their industry backing leave me wanting...let's hope #3 wraps things up.

I can make this quick. The final article was published online (2008) ahead of the Oral Oncology print yet featured no new evidence since the 2003 review. The author suggested there is no epidemiological evidence that mouthwash causes oral cancer.

Summing It Up:
  •  None of these studies address issues of reverse causation. It is likely (think about it...) that the onset of oral health issues (cancer, lesions, etc) result in greater use of mouthwash, and not the other way around.
  • Studies do not differentiate between alcohol-based and other mouthwash types, weakening the claim that it is the alcohol-based mouthwashes that are the culprit.
  • There is no clear relationship between quantity or frequency of mouthwash use and greater risk of oral cancers.
  • More rigorous studies are needed to suggest that the relationship is not a result of recall bias, under-estimation of tobacco or alcohol use, and other potential confounders.
I'll stick with my mouthwash of choice -- for now. Of course, if you are really interested in oral health issues check out the source articles for yourself!

PS. If someone can send me that Australian journal article I'd love to take a look!

Update: So I took a look at the Australian Dental Association article, which suggested that there is sufficient evidence to implicate high-alcohol content mouthwashes in the development of oral cancer. However, the studies they cited were not recently published, leading me to believe that the evidence upon which they base their claims are the same ones that these previous lit reviews reject. It is possible that high-alcohol containing mouthwash is dangerous for certain vulnerable groups. However, more rigorous scientific evidence should be produced to support that hypothesis.

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