Rats given varying doses of aspartame -- the second most widely used artificial sweetener in the world -- experienced a statistically significant increase in the incidence of malignant tumors, lymphomas and leukemias in a study slated for publication in Environmental Health Perspectives.

The study's authors are calling for an "urgent re-evaluation" of the current guidelines for consumption of this compound.

"Our study has shown that aspartame is a multipotential carcinogenic compound whose carcinogenic effects are also evident at a daily dose of 20 milligrams per kilogram (mg/kg) of body weight," the authors write, "notably less than the current acceptable daily intake for humans." Currently, the acceptable daily intake for humans is set at 50 mg/kg in the United States and 40 mg/kg in Europe.

More Than 200 Million People

Aspartame is found in more than 6,000 products, including carbonated and powdered soft drinks, hot chocolate, chewing gum, candy, desserts, yogurt and tabletop sweeteners, as well as some pharmaceutical products like vitamins and sugar-free cough drops.

More than 200 million people worldwide consume the sweetener. It has been used for more than 30 years, having first been approved by the Food and Drug Administration (FDA) in 1974.

Earlier research on the carcinogenicity of aspartame performed by its producers has been negative.

In the latest study, investigators administered aspartame to rats by adding it to a standard diet. They began studying the rats at eight weeks of age and continued until the spontaneous death of each rat. This study followed more animals over a longer period than did earlier research.

Treatment groups received feed that contained concentrations of aspartame at dosages simulating human daily intakes of 5,000, 2,500, 500, 100, 20 and 4 mg/kg body weight. Groups consisted of 100 males and 100 females at each of the three highest dosages, and 150 males and 150 females at all lower dosages, as well as controls.

The experiment ended after the death of the last animal at 159 weeks. At spontaneous death, each animal underwent examination for microscopic changes in all organs and tissues, a process different from the aspartame studies conducted 30 years ago and one that was designed to allow aspartame to fully express any carcinogenic potential.

Extensive Evidence of Malignancies

The treated animals showed extensive evidence of malignant cancers, including lymphomas, leukemias and tumors at multiple organ sites in both males and females.

The increase in lymphomas and leukemias may be related to one of the metabolites in aspartame -- namely methanol -- which is metabolized in both rats and humans to formaldehyde, the authors speculate. Both methanol and formaldehyde have shown links to lymphomas and leukemias in other long-term experiments.

"In our opinion, previous studies did not comply with today's basic requirements for testing the carcinogenic potential of a physical or chemical agent, in particular concerning the number of rodents for each experimental group (40-86, compared to 100-150 in the current study) and the termination of previous studies at only 110 weeks of age of the animals," the authors conclude.