The National Consumer League, a Washington consumer-advocacy group, filed a formal complaint with the Federal Trade Commission requesting it investigate Coca-Cola's marketing claims for Vitamin Water. The league said the brand touts more benefits than it can deliver.
"Vitamin Water: Flu shots are so last year," reads one advertising poster for the product.
In its complaint, the league said Vitamin Water ads say the drink not only promotes a healthy immune system but can also replace the flu shot.
"It's not only deceptive but potentially dangerous to consumers," said Courtney Brein, a food safety and nutrition fellow at the National Consumers League. "There's a difference between stating that certain elements of a product are good for you and implying that the product will actually prevent the consumer from catching the flu or coming down with the common cold."
With more than $700 million in sales last year, Vitamin Water has become one of the most popular sports drinks. Coca-Cola said in a statement that the content of its beverages is clearly marked on the label.
"Vitamin Water has always had a fun, humorous and engaging personality," the company said in a statement. "And our ads reflect that."
But some legal experts said it's easy to blur the line between clever advertising and overpromising.
"If you talk about what's in your product, then it has to be there," said Howard Beales, an associate professor of strategic management and public policy at the George Washington University School of Business. "If you talk about the effects of that substance, then you have to have evidence that documents the substance really does have those effects."
Research suggests the evidence as to whether the vitamins in Vitamin Water -- mainly vitamin C and zinc -- work to suppress the flu is conflicting. But there is no evidence that the drink can prevent the flu or is as effective as a flu shot.
"The best way to get your vitamins is through a balanced diet or a supplement," said Dr. Richard Besser, ABC News' chief health and medical editor. "And the best way to prevent the flu is to get a flu shot."
And then there's the sugar and calories to consider too. Although the Vitamin Water label indicates 50 calories per serving, one bottle amounts to 2.5 servings, which adds up to around 125 calories. One regular-size bottle of Vitamin Water also contains nearly 30 grams of sugar.
"For that, you may as well have a Hershey's milk chocolate bar, which has only 24 grams of sugar by comparison," said Besser.
While sports drink ads may claim extraordinary health benefits, Besser said these drinks don't possess anything more remarkable than what regular water can provide, and he cautioned against letting kids drink sugar sweetened sports drinks, including Vitamin Water, regularly.
"If you want to get hydrated after playing sports or exercising, turn on the tap," said Besser. "What you mainly need is regular, plain old water."