Debate over the safety of aspartame is heating up again, after African scientists published a review in this month's European Journal of Clinical Nutrition suggesting the artificial sweetener could be harmful to the brain.

"The aim of the study was to discuss the direct and indirect cellular effects of aspartame on the brain, and we propose that excessive aspartame ingestion might be involved in the pathogenesis of certain mental disorders, and also in compromised learning and emotional functioning," wrote scientists from the University of Pretoria and the University of Limpopo.

The review was first published online in August 2007, just before a contradictory report was made public in the September 2007 issue of the journal Critical Reviews in Toxicology. Considering over 500 studies, scientists concluded that aspartame is safe at current levels of consumption: "No credible evidence was found that aspartame is carcinogenic, neurotoxic, or has any other adverse effect on health when consumed even at quantities many times the established ADI [Acceptable Daily Intake] levels."

The Center for Science in the Public Interest called those findings "perfectly predictable," pointing out that the review was sponsored by an aspartame manufacturer and conducted by "industry-friendly researchers" who wholeheartedly endorsed studies that did not find evidence of carcinogenicity and identified every possible flaw in studies that did. The organization said the U.S. National Toxicology Program or another independent agency "should retest in well-designed studies this controversial artificial sweetener that is consumed by hundreds of millions of people around the world."

The United States approved aspartame in 1981, and the Food and Drug Administration has maintained that it is safe. FDA experts have said there is no scientific evidence supporting a link between aspartame and cancer. In 2005, the European Ramazzini Foundation published its findings from a long-term feeding study on aspartame in rats. The scientists concluded that aspartame causes leukemia and lymphoma. FDA reviewed the data and found that it did not support ERF's conclusion or provide evidence to alter FDA's position that aspartame is safe.

The recent review on cellular effects of aspartame on the brain, however, found that changes occur with high consumption levels. For example, the regional concentration levels of neurotransmitters like norepinephrine, epinephrine and dopamine are impacted. The report's authors say those changes could be the reason for headaches, insomnia, seizures and neurological effects some aspartame users encounter. "Previously, it has been reported that consumption of aspartame could cause neurological and behavioral disturbances in sensitive individuals," they wrote.

The scientists concluded that more testing is needed.