But food industry officials point out that many other studies have found no link between aspartame and cancer.
The rats in the study were fed various doses of aspartame throughout their lives. In female but not male rats, lymphoma and leukemia were significantly associated with daily aspartame doses as low as 20 milligrams (mg) per kilogram (kg) of body weight. And there was a trend toward these cancers at doses as low as 4 mg/kg of body weight.
To reach a dose of 20 mg/kg, a 140-pound woman would need to drink three cans of diet soda a day. A 180-pound man would need to drink four cans of diet soda a day.
And diet soda isn't the only source of aspartame. The sweetener is in thousands of products, ranging from yogurt to over-the-counter medicines.
The average person consumes about 2 or 3 mg/kg aspartame each day. However, that figure goes way up for children and young women.
The study comes from an independent research team led by Morando Soffritti, MD, scientific director of the European Ramazzini Foundation of Oncology and Environmental Sciences in Bologna, Italy.
"What I am recommending is for healthy children and women -- if they do not have diabetes -- to avoid consumer use of aspartame," Soffritti tells WebMD. "We cannot continue to use aspartame in 6,000 types of products, soft drinks, yogurt, and whatever."
Consumer Group Reacts
A consumer watchdog group, the Center for Science in the Public Interest, has called for FDA action. At a minimum, the FDA should start its own studies and warn consumers of the potential danger, says CSPI Executive Director Michael F. Jacobson, PhD.
"The U.S. government really should analyze this study very carefully. If it is accepted as top quality, it could lead to a ban on aspartame," Jacobson tells WebMD. "I think a lot of companies are going to see the writing on the wall from this study and switch to newer artificial sweeteners. Meanwhile, I think consumers should switch to Splenda, the sweetener known as sucralose."
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."