But Jacobson urges consumers not to panic.
"The risk to an individual is quite small," he says. "So people shouldn't fear that if they have one diet soda a day they are going to develop cancer. And I must say, the one qualm I have about the study is they found an increased risk of cancer at such a low level of exposure. If aspartame were that potent a carcinogen, I wonder if we wouldn't be seeing a real epidemic of cancer."
Soffritti has presented his findings to the European Food Safety Authority. In its 2002 review of aspartame safety, the EFSA found no cause for alarm. It promises that the new data will get a "high priority" evaluation.
"EFSA does not consider it appropriate to suggest any change in consumers' diets relative to aspartame on the basis of the information it currently has," the EFSA announced on July 14.
Low-Calorie Industry: No Cause for Alarm
The new findings fly in the face of all previous studies of aspartame safety, says the Calorie Control Council, an international association representing the low-calorie and reduced-fat food and beverage industry.
The Soffritti study findings "are not consistent with the extensive scientific research and regulatory reviews done on aspartame," the CCC says in a statement. "Aspartame has been used by hundreds of millions of consumers around the world for over 20 years. With billions of man-years of safe use, there is no indication of an association between aspartame and cancer in humans."
The CCC points to four long-term studies on aspartame that failed to find any relationship between aspartame and any form of cancer.
It's true that reports linking brain and breast cancer to aspartame had little merit, says blood-cancer specialist Martin R. Weihrauch, MD, of the University of Cologne, Germany. Last year, Weihrauch reported on his analysis of all published studies on artificial sweeteners in the Annals of Oncology.
"The entire stuff about brain tumors and breast cancer was really nonsense, Weihrauch tells WebMD.
So what does he think of the new study linking aspartame to leukemia and lymphoma?