First up a warning – this is a technical, in-depth post and not the easiest read. It’s complex as it’s about something very complex indeed; the recent Cochrane review on xylitol and tooth decay.
If you don’t know it already, Cochrane is a global network of researchers, medical professionals and other associated parties that produces summary views on specific health issues. There is a tonne of clinical research out there and often hundreds, if not thousands of papers studying the same subject. Cochrane analyses all of the good research on the topic (aka meta-analysis), coming to its own conclusion. It’s the gold standard of this type of analysis and plays a very important role in helping people make informed decisions around complex health issues.
Last week Cochrane released a report on xylitol saying that, while there is some evidence that fluoride toothpaste containing xylitol may reduce tooth decay (aka caries), the evidence around other products (like mints and gum) “did not allow us to conclude whether or not any other xylitol-containing products can prevent tooth decay”.
This came as quite a surprise to us as xylitol has been the subject of many many positive clinical trials. As we said, the report itself is complicated and we need a bit of time to pull together a thorough response. But as we’re already getting asked about it, here’s our view given what we know so far.
The most important thing is that the report is definitely not saying that research shows xylitol does not reduce tooth decay. There is no doubt that there’s lots of compelling research concluding that xylitol (consumed in the right way) does reduce decay. What the report is saying is that the vast majority of this research could not be included in this meta-analysis. Cochrane found over 900 studies on xylitol and deemed only 10 eligible. Of those 10, zero looked at xylitol chewing gum.
Why? Great question as this is the key to the report’s findings. Here’s what we know…
i) Many important xylitol studies look at the risk factors that cause decay as opposed to decay itself. In particular the effect of xylitol on Mutans Streptococci (MS) – one of the main bacteria that forms plaque, which in turn causes decay. The logical theory being that MS are a proxy measurement for caries as they are a major cause of it; if you can affect this type of bacteria you can reduce decay. Cochrane however has not included any studies on risk factors such as MS and only looked at studies directly about caries. This is HUGELY significant for the findings. There’s no doubt that if xylitol reduces MS, it helps reduce decay, but the report does not take this into account.
ii) One of the benefits of a meta-analysis is the ability to combine studies with similar results. But even when only looking at tooth decay, there are many different outcomes that can be measured. For example, some studies simply count whether there was dental decay or not. Others count dental decay as any form of demineralisation and grade how mild or advanced it is. Other studies looked at incremental decay; the net difference in dental decay before and after the research. And some count only teeth where there is obvious dental decay into the dentine level. The consequence of this is that lots of studies couldn’t be included as they had different outputs that couldn’t be compared with each other.
iii) The review has very strict criteria around what is and isn’t acceptable research design. For example Cochrane are only interested in research carried out as “Randomised Controlled Trials” and there isn’t a large body of research that investigates the clinical efficacy of xylitol using this specific methodology. This has a lot to do with the age of the xylitol research as it wasn’t until the late 20th century that RCTs became the recognised standard for clinical interventions. It was 1996 that the recommendations around RCTs were made (as part of the CONSORT statement) and – like many innovations in health care (and other areas) – it takes a long time for recommendations to be implemented. RCTs also mean that one set of subjects will receive a less effective treatment, or possibly none at all, a situation which may sometimes be ethically questionable and means there can be pressure not to go down the RCT route. There was also important research ruled out because of potential “bias”; where results may have been influenced by high dropout rates, or exposure to factors other than the interventions of interest, unclear selection methods for participants etc. It is very difficult to conduct research without any form of bias and again the age of many of the important xylitol studies means they were conducted before tighter guidelines were released covering this very complex area.
In summary, due to its own criteria, this Cochrane report can only look at a very small body of research around xylitol which is why it was not able to reach a definitive positive conclusion. To be clear we’re not criticising Cochrane or disputing their criteria. They are awesome and they know their stuff. We just want to make sure people understand the meaning of the conclusions and that it definitely does not mean that xylitol isn’t an effective tool for helping you keep your teeth healthy.
And of course other reviews looking in to xylitol’s benefits have reached a positive conclusion. In 2008, the scientific panel of EFSA, the EU’s Food Safety Authority that now strictly governs all health claims, concluded that 100% xylitol gum has been shown to reduce plaque.
We’ll be back with more once we’ve finished our full review of the Cochrane report. In the meantime, if you want to add any info, questions or challenges please add a comment.
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