You may have heard that getting a vitamin B₁₂ injection will boost your immunity, but no studies have been conducted to prove that it can protect you from the cold or flu. “Most people who eat healthily are getting enough vitamin B,” says Gershwin. “A vitamin B₁₂ shot for otherwise healthy people is a waste of money.”

As for sugar-free vitamin waters, while they are better than sugary sodas, they contain only trace amounts of vitamins—nothing that will prevent a cold or boost short-term immunity, says Aileen Burford-Mason, an immunologist and the president of the Holistic Health Research Foundation of Canada.