An article on WebMD states that "extremely" high doses of xylitol might cause tumors:

There is some concern that extremely high doses for long periods of time (more than three years) might cause tumors.

The article does not provide references nor quantify what exactly is meant by "extremely high doses".

I was able to find only one study in male mice that supports this conclusion:

Xylitol, a sucrose substitute made from birch trees that has been touted for its tooth decay preventive properties, apparently has caused some cancers in laboratory animals. Preliminary findings from two-year chronic toxicity studies show an increase in urinary bladder stones in male mice fed xylitol in doses of 10% and 20% of their total diet. Some of the mice that developed bladder stones also had bladder inflammation and benign and malignant tumors. Female mice developed no unusual symptoms, and neither did male mice fed xylitol as 2% of their diet.

It is unlikely that WebMD is relying on this study as evidence for a possible link between xylitol consumption and tumor formation as I don't think 10-20% of dietary intake constitutes an "extremely high dose". Moreover, the study was conducted for only two years (not three).

In contrast, a different study showed that tumor cells in the liver have difficulty converting xylitol to a usable source of energy. However, the study did not show that this necessarily translates into decreased tumor growth. Neither did it show that xylitol reduces the overall incidence of tumors in humans.

A report published in Feb 1988 by the Diabetes Journals states that:

However, chronic intake of xylitol in animals has been shown to be associated with tumor induction and other pathology. Consequently, use of xylitol is currently curtailed in the United States, and no recommendation concerning its use can be made

Is there a possible link between xylitol and tumor formation? Or perhaps I should phrase my question differently:

Is there sufficient evidence that xylitol consumption does not increase the risk of tumors in humans?

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    Two issues: the volume in those animal studies is ridiculously high (people would need to consume kg for equivalent doses); if normal levels of xylitol caused cancer in people, there should be some epidemiological evidence as plenty of people have been using it for a long time. – matt_black Jan 12 at 12:49
  • @matt_black I don't have access to the actual study so I don't know the precise quanitity of xylitol they were feed. All I see is that it constituted 10% of their diet. Translated to human terms this would be equivalent to 100 calories of xylitol on a 1,000 calorie diet and 200 calories of xylitol on a 2,000 calorie diet. Please clarify, how did you arrive at a kg of xylitol? – S.O.S Jan 12 at 16:29
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    Yous don't count dietary consumption in calories, especially when considering artificial or low-calorie sweeteners (which is what xylitol is) where the calorific content is either low or meaningless. You count by mass. I just did a crude calc of what 20% of a diet might be by mass (people consume several kg/day if you include fluids and I was rounding up, might be more realistic to claim 100s of grams of xylitol as 20% of dietary intake equivalent which would cause serious digestive problems). – matt_black Jan 12 at 16:41
  • @matt_black "you don't count dietary consumption in calories" -- I would agree to that sentiment if we were dealing with no calorie artificial sweeteners. Xylitol still has 2.4 calories per gram (which is only 40% less than table sugar). Also, the study showed an increase in cancer even at 10% of total dietary intake. Finally, I don't understand why you are including "fluids" in the calculation. My impression was that the researchers substituted some of the "food" in their diet with xylitol (but again I don't have access to the actual study so it is possible I missed something..) – S.O.S Jan 12 at 16:58
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    Some studies used more than 10%. Even if you exclude fluids, that is a very large proportion of your diet. So the relevance to people of overfeeding rats with a ridiculous diet is severely dubious, especially since the rats are likely bred to be especially susceptible to cancer. If people took those doses they would probably suffer from serious deficiency diseases first as it is a laxative in large doses. Besides, if xylitol is carcinogenic we will have to stop eating plants and fruits as it is common in them. – matt_black Jan 12 at 17:10

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