In Glaceau Vitamin Water's new ad campaign, flu shots are described as "so last year." One poster shows three Vitamin Water bottles aligned with the text, "more vitamin C...more immunity...less snotty tissues." In a TV commercial, a woman brags about getting to use all her sick days to hang out with her boyfriend due to the zinc and vitamin-C present in Power-C Vitamin Water, which she says have kept her safe from colds and flu.

Despite the outcry of such groups as the National Consumers League, which describes the implication that Vitamin Water can replace flu vaccination as "dangerously misleading," Glaceau has stuck by its message. So who's right?

Life's Little Mysteries asked Simin Meydani, director of the Nutritional Immunology Laboratory at the Jean Mayer USDA Human Nutrition Research Center at Tufts University: Do zinc and vitamin C supplements really help prevent colds and flu ?

"The jury is out on that. There is some evidence that zinc is important in terms of pneumonia, but specifically for colds and flu, we don't have adequate information to say that. There is some evidence on either side of the argument," said Meydani, who has published seminal works on the immunal effects of zinc and other vitamins.

"As for vitamin C, in terms of colds and flu, it's similar to what we know about zinc: In certain settings it may be effective, and at other times not," she went on. "The problem is, many studies that have been done are of a small sample size or didn't have adequate control, so it's hard to say the benefits that were observed were entirely due to vitamin C."

As for the claim that Vitamin Water obviates flu vaccines , this assertion was gasp-inducing for our expert. "If they are claiming that Vitamin Water can replace flu vaccines that's very irresponsible of them. Nutritional intervention should be considered in terms increasing overall health but not in terms of replacing vaccines."

"Very irresponsible," Meydani reiterated.

Got a question? Send us an email and we'll look for an expert who can crack it.

Follow Natalie Wolchover on Twitter @nattyover