The safety of stevia has been called into question again after scientists at the University of California said further tests were needed on potential cancer causing properties before the sweetener is used in food and drink.
Beverage giants Coca-Cola and PepsiCo are poised to launch products containing their own brands of rebiana, which is from the stevia plant, but it is argued that more evidence is needed to show that the sweetener is safe.
A review of safety data was carried out by the toxicologists on behalf of the Center for Science in the Public Interest. It said that carcinogenicity studies have not found stevioside (which differs slightly from rebiana) to be carcinogenic in rats but further studies on rebiana, including a study on mice, are needed.
This is partly because several genotoxicity studies found that stevioside and steviol cause mutations, chromosomal damage, and DNA breakage which “indicate the need for greater reassurance of noncarcinogenicity” as rebiana might cause similar problems, or cancer, in humans.
The Food and Drug Administration's (FDA) guidelines advise testing potential food additives on two rodent species, usually rats and mice. But rebiana (rebaudioside A) has only been tested on rats
The study concluded that the FDA should require carcinogenicity and toxicology studies both in rats and mice before accepting rebaudioside A as generally recognized as safe (GRAS) or approving it as a food additive.
The Center for Science in the Public Interest has now written to the FDA echoing the reports conclusions.
CSPI executive director Michael F Jacobson, said: “A safe, natural, high-potency sweetener would be a welcome addition to the food supply.
“But the FDA needs to be as sure as possible that rebiana is safe before allowing it into foods that would be consumed by tens of millions of people.
“I am not saying that rebiana is harmful, but it should not be marketed until new studies establish that it is safe.”
Older tests suggested stevia might interfere with reproduction, although more recent studies did not find such problems.
Rebiana is the sweetest, purest part of the leaf from the South American stevia plant, which is approximately 200 times as sweet as sugar.
Stevia, which is permitted for sale in the US as a dietary supplement on the basis of its low glycemic index, is yet to have FDA GRAS status for use in food and beverages.
The US market for stevia is estimated to be worth about $60m, a figure analysts say could triple with FDA GRAS. Currently the biggest markets for stevia are Japan and Korea.
Last month it was announced that PepsiCo has joined with the Whole Earth Sweetener Company to launch its rebiana sweetener PureVia.
Meanwhile Coca-Cola has teamed up with Cargill to use its rebiana brand, called Truvia.
Cargill is already selling Truvia online as a table-top sweetener but the beverage companies are yet to sell drinks with the sweetener in the US.
A spokesman for PepsiCo said: “Everyone agrees that no ingredient should be marketed to consumers until its safety has been proven.
“While we believe the full body of evidence presented to the FDA by multiple sweetener manufacturers demonstrates the safety of this ingredient, ultimately it’s up to the FDA to decide.”
Cargill and Merisant have notified the FDA that rebiana should be GRAS. However, the US's largest supplier of stevia Wisdom Natural Brands has said that its stevia-based sweetener Sweet Leaf is self affirmed GRAS, without FDA notification, and the ingredient will be available in soda or food products by the end of the year.
The study, called ‘Toxicology of Rebaudioside A: A Review’, is by Sarah Kobylewski, a doctoral student, and Curtis D Eckhert, Ph.D, professor of environmental health sciences and molecular toxicology at the University of California.
It noted conflicts of interest in some of the recent research on rebiana, as it was sponsored by Cargill, and said that the the FDA to obtain independently conducted tests.
The debate around stevia has also raised issues about the GRAS system in general. Jacobson said: "The whole issue of what gets GRAS status needs to be reviewed by Congress.
“It’s crazy that companies can just hire a few consultants to bless their new ingredients and rush them to market without any opportunity for the FDA and the public to review all the safety evidence.”