In the most recent round of the decades-long debate about vitamin C and the common cold, a review of 30 studies found that use of the vitamin was shown to cut cold risk in half for marathon runners and others exposed to extreme physical stress. But for the general population, its preventive powers were marginal. It's important to evaluate the latest results in the context of other studies, says the Linus Pauling Institute's Stephen Lawson.
Whereas "many of the studies followed people for a short period of time," he notes, a five-year Japanese study that followed 244 people showed a 66 percent reduction in cold incidence for people taking 500 mg daily. "We're all biochemically different," adds Lawson. "Some people may benefit a lot from extra vitamin C; others may benefit less." For now, many experts are keeping their advice intact. Mark Moyad, M.D., of the University of Michigan Medical Center recommends taking a 500 mg daily supplement year-round to harness C's immune-boosting benefits. For food sources of C, look to kiwis, citrus, and broccoli.