A huge federal study in people — not rats — takes the fizz out of arguments that the diet soda sweetener aspartame might raise the risk of cancer.
No increased risk was seen even among people who gulped down many artificially sweetened drinks a day, said researchers who studied the diets of more than half a million older Americans.
A consumer group praised the study, done by reputable researchers independent of any funding or ties to industry groups.
"It goes a fair way toward allaying concerns about aspartame," said Michael Jacobson, head of the Center for Science in the Public Interest, which had urged the government to review the sweetener's safety after a troubling rat study last year.
Findings were reported Tuesday at a meeting of the American Association for Cancer Research.
Research in the 1970s linked a different sweetener, saccharin, to bladder cancer in lab rats. Although the mechanism by which this occurred does not apply to people and no human risk was ever documented, worries about sugar substitutes in general have persisted.
They worsened after Italian researchers last year reported results of the largest animal study ever done on aspartame, involving 1,800 lab rats. Females developed more lymphomas and leukemias on aspartame than those not fed the sweetener.
The new study, by scientists at the National Cancer Institute, involved 340,045 men and 226,945 women, ages 50 to 69, participating in a research project by the National Insitutes of Health and AARP, formerly known as the American Association of Retired Persons.
From surveys they filled out in 1995 and 1996 detailing food and beverage consumption, researchers calculated how much aspartame they consumed, especially from sodas or from adding the sweetener to coffee or tea.
Over the next five years, 2,106 developed blood-related cancers such as lymphoma or leukemia, and 376 developed brain tumors. No link was found to aspartame consumption for these cancers in general or for specific types, said Unhee Lim, who reported the study's findings.
The dietary information was collected before the cancers developed, removing the possibility of "memory bias" — faulty recollection influenced by knowing you have a disease.
"It's very reassuring. It's a large study with a lot of power," said Richard Adamson, a senior science consultant to the American Beverage Association, the leading industry group.
The Center for Science in the Public Interest still warns about one potential hazard of aspartame use: thinking that calories "saved" from using a sugar substitute justify "spending" more on unhealthy foods.
"Drinking a diet soda at lunch does not mean it's okay to have a larger dessert at dinner," the group's Web site warns.