The announcement this week by a World Health Organization agency that the artificial sweetener aspartame — used in such low-calorie products as Diet Coke, Trident gum and sugar-free Jell-O — is "possibly carcinogenic to humans" has many wondering if the food additive is safe to consume.

Thursday's announcement from WHO's International Agency for Research on Cancer, or IARC, reclassifies aspartame, which has been in wide use since the 1980s and is sold under such brand names as NutraSweet and Equal.

At a news conference in Geneva, Dr. Francesco Branca, director of the Department of Nutrition and Food Safety at the WHO, said that concern was only for "high consumers" of diet soda and other foods containing aspartame and said that IARC had simply "raised a flag" for more research to be done.

Dr. Mary Schubauer-Berigan, a senior official at IARC, emphasized that "it shouldn't really be taken as a direct statement that indicates that there is a known cancer hazard from consuming aspartame."

The recommended acceptable daily intake of aspartame has not changed

Meanwhile, the Joint FAO/WHO Expert Committee on Food Additives (JECFA), which is jointly administered by WHO and the Food and Agriculture Organization of the United Nations (FAO), said its acceptable daily intake of aspartame has not changed. It says to exceed that limit, an adult weighing 154 pounds would need to consume nine to 14 cans of a diet soft drink containing 200 or 300 mg of aspartame.

The U.S. Food and Drug Administration says it's aware of the conclusions of both the IARC and JECFA, but that "does not mean that aspartame is actually linked to cancer."

The WHO uses a four-tiered system of classification: carcinogenic; probably carcinogenic; possibly carcinogenic; and non-carcinogenic.

As an article in Science notes, "Other substances classed as 'possibly carcinogenic' include extracts of aloe vera, traditional Asian pickled vegetables, some vehicle fuels and some chemicals used in dry cleaning, carpentry and printing. The IARC has also classified red meat as 'probably carcinogenic' and processed meat as 'carcinogenic.'"

Experts say more research is needed

"What this means is that more research needs to be done to ascertain if there is a link to aspartame," says Marjorie McCullough, senior scientific director of epidemiology research at the American Cancer Society.

Toxicologist Daniele Wikoff, a principal scientist at ToxStrategies, has been involved in a number of studies of aspartame commissioned by the American Beverage Association, or ABA, a lobbying group representing the beverage industry. She says the bottom line coming out of Thursday's news conference in Geneva "is basically there's no change."

The studies on aspartame cited by IARC "are really a small, small part of the overall evidence base." The full picture "is much larger, demonstrating safety," Wikoff says. "The overwhelming majority of those studies support lack of association" between aspartame and cancer.

Kevin Keane, the ABA's interim president and CEO, says it's "disappointing" that the IARC has sowed confusion in the minds of consumers. "The FDA and 95 food safety agencies around the globe have found aspartame to be safe," he says. "Consumers should be confident going forward."

However, Dr. Dariush Mozaffarian, a cardiologist and professor at Tufts University's Friedman School of Nutrition Science and Policy, describes the research into aspartame's effect on humans as "woefully inadequate."

He points to the "very limited number" of randomized controlled trials looking at aspartame and other artificial sweeteners. "What's concerning is while there's been an explosion in their use in foods, there has not been an explosion in the science to be sure they're safe."

Consumers should still limit sugary regular soda

Dr. Frank Hu, a professor of nutrition and epidemiology at the Harvard School of Public Health, also has concerns about how well the possible effects of aspartame have been studied. He says the problem is twofold.

"It's difficult to do studies in free living populations to get a great estimate of how much people actually consume," he says.

Another challenge, Hu says, is that in the case of rare cancers such as liver cancer, which the WHO specifically noted, researchers need "hundreds of thousands of people, perhaps millions of people to be followed and to obtain sufficient statistical power to get reliable answers."

The aspartame focus has been largely on low-calorie diet sodas, but what about its use in other beverages?

"If you put two packets of sweeteners into your coffee or tea, I don't think that's going to be a problem for the vast majority of people," Hu says.

For Tuft's Mozaffarian, despite his concerns, he says that for someone who can't break a soda habit, it's still better to drink the diet variety. "We know that high amounts of regular soda is really, really bad for weight gain or obesity or diabetes for risk of heart attack events."

"So ... yes, better to switch to diet [soda]," he says. "But it's even better then to switch from diet to unsweetened sparkling water."