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?