WASHINGTON—U.S. 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-flavoured 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. 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 U.S. 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, New Jersey, with headquarters in London and in Rotterdam, Netherlands.

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

Calls to Plano, Texas-based Dr. Pepper Snapple Group were not immediately returned Tuesday. Calls placed to Unilever’s Englewood Cliffs, N.J.-based offices also were not immediately returned. The company is headquartered in London, England, and Rotterdam, Netherlands.

Once a niche market, nutrient-enriched beverages have grown into a multibillion dollar business. In recent years, the FDA has begun cracking down on food companies that overstate the benefits of their products.