Vitamin C is especially popular among Americans during cold season, but scientists aren’t convinced of the benefits.

According to the Nutrition Business Journal, Americans spend more money on vitamin C, roughly $330 million a year, than on any other immune-boosting supplement, maybe because it’s been around so long, the Los Angeles Times reported.

“People take vitamin C during cold and flu season because since the 1950s, that’s pretty much what we’ve all been told to do,” said Daniel Fabricant, vice president of scientific and regulatory affairs for the Natural Products Assn.  “It’s just in our subconscious mind-set.”

Scientists have been going back and forth on whether Vitamin C is beneficial at preventing or treating the common cold for just about as long, the LA Times said.

Last summer, the Cochrane Collaboration, a nonprofit organization that reviews the science on health topics, reviewed more than 50 well-designed, published studies on vitamin C and the common cold. The researchers found that taking at least 200 milligrams of vitamin C on a daily basis doesn’t reduce the odds of getting a cold. However, they did find that it increases recovery time by about 8% in adults, and 13.6% in children.

The reviewers also discovered that while vitamin C doesn’t keep colds at bay in most cases, it cuts the risk of colds in half in people under great physical stress, LA Times reported.

The Cochrane reviewers also concluded that while some evidence also suggests that taking a very large dose of C (up to 8 grams) at the onset of a cold could shorten the duration of infection or lessen symptoms, more research was needed to confirm it.

If you’re not one of those under great physical stress, the researchers say Vitamin C probably offers little in the way of cold prevention, but it probably isn’t harmful, according to Penn State’s Dr. Ian Paul.

The LA Times also said that high doses of vitamin C (three to five grams at a time) can cause gastrointestinal effects, including diarrhea.