WASHINGTON –  Federal health regulators have issued warnings to the makers of Canada Dry ginger ale and Lipton tea for making unsubstantiated nutritional claims about their green tea-flavored beverages.

In a warning letter issued Aug. 30, the Food and Drug Administration takes issue with the labeling of Canada Dry Sparkling Green Tea Ginger Ale. The agency issued a similar letter Aug. 23 to Unilever Inc., over website and product labeling for its Lipton Green Tea.

Food processors increasingly have been adding vitamins and nutrients to their products to make them more appealing to health-conscious consumers. But the FDA letter to Dr. Pepper Snapple Group, which makes Canada Dry, states that the agency "does not consider it appropriate to fortify snack foods such as carbonated beverages." Furthermore, the agency states that the soft drink does not meet federal requirements to carry the claim that the drink is "enhanced with 200 mg of antioxidants from green tea and vitamin C." According to FDA regulations, the ingredients in Canada Dry's product "are not nutrients with recognized antioxidant activity."

The FDA letter to Unilever takes issue with a company website that mentions four studies that showed a cholesterol-lowering effect with tea. According to the agency, the labeling is misleading because it suggests Lipton tea is designed to treat or prevent disease. The agency also cites antioxidant labeling claims on the company's Lipton Green Tea, which do not follow federal guidelines.

The agency asks executives from both companies to respond to the citations within 15 days and to outline their plans for addressing the problems.

A spokesman for Plano, Texas-based Dr. Pepper Snapple Group said in a statement the company looks "forward to working with the FDA and addressing the issues raised."

Unilever issued a similar response. The company's U.S. operations are in Englewood Cliffs, N.J.-based, with headquarters in London and Rotterdam, Netherlands.

Once a niche market, nutrient-enriched beverages have grown into a multibillion dollar business that includes everything from calcium-enhanced orange juice to energy drinks containing ginseng, ginkgo and other organic products.

In recent years, the FDA has begun cracking down on food companies that overstate the benefits of their products.

The FDA generally endorses health claims on foods only after government researchers have verified that the products help prevent actual disease. Food containing oats, for example, can carry the FDA-approved claim, "may reduce risk of heart disease."

The FDA regularly issues warning letters to companies that do not follow regulations for manufacturing and marketing. The letters are not legally binding, but the agency can take companies to court if they are ignored.