Nov. 18, 2005 - A study in rats links the popular artificial sweetener aspartame to a wide range of cancers, but industry officials charge that the research is badly flawed.
Aspartame is found in the low-calorie sweetener Equal and in many other sugar-free products under the brand name NutraSweet. It is the second best-selling nonsugar sweetener in the world.
Researchers in Italy concluded that rats exposed to varying doses of aspartame throughout their lives developed leukemias, lymphomas, and several other cancers in a dose-dependent manner.
They report that the product is a potential cancer-causing agent to humans even at levels that are less than half of what is considered safe by the U.S. government.
The study appears in the Nov. 17 issue of the journal Environmental Health Perspectives, which is published by the National Institute of Environmental Health Sciences (NIEHS) of the U.S. Department of Health and Human Services.
But critics charged that the investigators did not follow the guidelines for scientific study outlined by the NIEHS' own research group, the National Toxicology Program. They further noted that the NTP's own animal studies involving similar levels of aspartame exposure showed no link between the sweetener and an increase in cancers.
And an NIEHS spokesperson said Friday that the agency had "no role in the design, performance, or interpretation" of the newly published study.
'Findings Speak for Themselves'
The study was conducted by researchers from the European Ramazzini Foundation, an independent group located in Bologna, Italy.
One hundred male rats and 100 female rats were followed from 8 weeks of age until their deaths from natural causes. The rats were fed aspartame at doses approximating a wide range of human consumption levels, from very low levels to very high.
Each rat was autopsied following its spontaneous death, and exposed animals were found to have a higher rate of leukemias, lymphomas, kidney and pelvic cancers and a brain cancer.
Researcher Morando Soffritti, MD, and colleagues called for an "urgent re-evaluation" of the current guidelines for the use of aspartame.
"The findings speak for themselves," he tells WebMD. "They show the potential carcinogenicity of aspartame in animals."
Soffritti said the fact that the rats in the study died of natural causes rather than being sacrificed at a specific point in their lives helped the researchers to better identify the cancer links.
But critics contend that this was a big problem with the study. Most cancer study guidelines recommend the sacrifice of research animals at specific ages -- in the case of the rats used in the study around 104 to 110 weeks.
That would be the equivalent of age 60 or so in humans. The last rat in the study died at 159 weeks of age.
"Rats, like people, develop a wide range of cancers in old age, and establishing whether there is a cause-and-effect relationship (at an age when cancers are common) is not possible," says Joe Poulos, a spokesman for Merisant, the company that makes the aspartame sweetener Equal.
"More than 200 toxicological and clinical studies have been conducted over the past 30 years, all of which have confirmed the safety of aspartame," he tells WebMD.
Widely Considered Safe
Poulos says that regulatory agencies in 130 countries have reviewed aspartame and found it to be safe.
Most scientific organizations that have weighed in on the question have come to the same conclusion, including the American Medical Association, the American Dietetic Association, the American Diabetes Association, and the American Cancer Society.
In its report on aspartame, the American Cancer Society concludes that "current evidence does not demonstrate any link between aspartame ingestion and increased cancer risk."
In the newly published study, Soffritti and colleagues speculated that methanol, which is a byproduct of aspartame, may explain the increase in cancers seen in the study. Methanol is metabolized in both rats and humans to form formaldehyde, which is a carcinogen.
Beth Hubrich, MS, MD, of the artificial sweetener-industry group Calorie Control Council, tells WebMD that all kinds of foods contain methanol. She calls the newly published study "seriously flawed."
"You can actually find six times more methanol in a glass of tomato juice than in a beverage sweetened with aspartame," she says. "And there is no difference in the way that methanol is metabolized by the body when it comes from aspartame or from some other source like tomato or orange juice."