Many products are marketed to prevent and treat colds and other viral upper respiratory infections. These range from plain vitamin C to fancier powders you mix with water for an effervescent drink. Unfortunately, evidence that these products show actual benefits is sparse.
Vitamin C is an important nutrient. Yet studies evaluating its effectiveness during acute illness show, at best, an 8 percent speedier recovery — meaning you’ll feel better 13 hours sooner during a typical seven-day illness. At worst, the studies demonstrate no benefit at all.
Some cold prevention products contain zinc. While an old study on its use in treating colds was promising, the results were questioned because a zinc product manufacturer funded the research.
No studies on zinc have since shown any benefit. What’s more, toxicity from taking high amounts of zinc (beyond what you’d normally get in a multivitamin) is a definite risk.
It’s hard to know whether taking these cold products might produce a placebo effect or if any perceived benefit is due to hydration and electrolyte replacement.
So while taking vitamins when you’re sick probably won’t hurt you, the best medicine still seems to be time, fluids and rest.