(Adds Hain, Coke comments, product details, byline)
By Kim Dixon
WASHINGTON, Sept 18 (Reuters) - U.S. health regulators warned Hain Celestial Group Inc. (HAIN.O) about a potentially unsafe herb in some of its teas, saying it might be dangerous to blood sugar, reproductive, cardiovascular and renal systems.
The U.S. Food and Drug Administration sent a letter to Hain, dated Aug. 17, calling the herb, a natural sweetener made from a South American herb called stevia, "an unsafe food additive." The agency released the letter on its Web site on Tuesday.
Stevia, derived from a South American herb and several hundred times sweeter than sugar but with no calories, is approved as a dietary supplement, but not as a food additive in the U.S.
Boulder, Colorado-based Hain said in a statement the FDA agreed that the company could change the products' labels to reflect that they are supplements and not food.
An FDA spokeswoman was not available for further comment.
Stevia is being eyed by big beverage makers looking for new low-calorie sweeteners. In May, Coca-Cola Co (KO.N) and Cargill Inc [CARG.UL] said they would work together to develop and market a new sweetener using stevia. While not approved as a food additive in the United States, stevia has been approved in a dozen other countries including Japan, China and Brazil.
The FDA letter said that although it has received requests to use stevia in food, "data and information necessary to support the safe use have been lacking."
It also said "literature reports have raised safety concerns," including those "about control of blood sugar and the effects on the reproductive, cardiovascular and renal systems."
Atlanta-based Coke spokeswoman Kari Bjorhus said the beverage giant and Cargill are working on scientifically establishing the safety of the herb.
The Celestial Seasonings-brand products cited by the FDA include the "Zingers" line of herbal teas.
The consumer group Center for Science in the Public Interest believes there is not enough data to support the safety of stevia in food.