According to the 2002 issue of "Biological and Pharmaceutical Bulletin," leaves pulled from the plant Stevia rebaudiana were used for centuries in South America as a sweetener in mate tea. Presently, stevia is gaining popularity in the United States as an alternative sweetening agent. Although the Food and Drug Administration, or FDA, does not support usage of stevia as a food additive, except in its purest form, stevia can be purchased as an unregulated dietary supplement.
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Four steviol compounds, naturally occurring molecules derived from stevia leaves, were tested for potential anti-cancer effects, according to Dr. Ken Yasukawa in the 2002 issue of "Biological and Pharmaceutical Bulletin. The steviol molecules successfully blocked the effects of 12-O-tetradecanoylphorbol-13-acetate or TPA in mice. TPA is a potent carcinogen capable of spurring cancer growth. By inhibiting the effect of TPA, extracted molecules from stevia might have an anti-cancer effect. More research is necessary.
Genotoxic studies are important experiments that focus on the toxicity of certain compounds on DNA integrity. If a compound is highly genotoxic, or highly damaging to DNA, this is often an indication of the cancer-causing ability of a compound. According to the 2009 issue of "Food and Chemical Toxicology," Dr. Lonnie Williams showed that rebaudioside A, one of the main compounds in stevia leaves, did not have any genotoxic effects, indicating that stevia is not likely carcinogenic.
According to the 2002 "Chemical and Pharmaceutical Bulletin," Dr. Tadamasa Terai explains that most of the compounds extracted from stevia leaves do not exhibit mutagenic or genotoxic effects that can cause cancer. However, they did observe that one specific stevia compound, stevioside, was converted into another molecule form by bacteria in lab rats' stomachs. This new compound exhibited mutatgenic effects. However, these results are far from conclusive. It is unclear how these findings extrapolate to humans.
The safety and cancer data on stevia is far from complete. Although it is largely considered safe, with some limited but possible anti-cancer effects, the data simply do not support any ties to cancer. Furthermore, even though the present data may not support the presence of dangerous side effects in regard to stevia usage, this could simply mean that the experiments have not yet been performed. Caution is advised.