You might not be taking enough of it to notice a difference

We’ve all heard that vitamin C wards off colds, or can at least shorten their duration. But is that just an old wives’ tale?

Now, science has tackled those claims, and came up with a conclusion: Vitamin C is effective at treating colds—but only if you take a substantial amount, researchers from Finland reported.

After crunching the numbers from previous studies, the researchers concluded that people taking 8 grams (g) of the vitamin a day shortened their colds by 19 percent, compared to a placebo group. Those taking 4 g per day shortened their colds by about half that amount.

While this study shows significant cold-shortening benefits to taking C, other prior ones didn’t find such a link. The possible reason? People in them may have been taking too low a dose of vitamin C, the researchers stated.

But at higher doses, there may be more benefits because vitamin C is an antioxidant, the study notes, and can boost the immune system. The vitamin has been shown to stop the replication of viruses, shutting down whatever nasty cold you’ve got brewing.

So, should you start popping mega doses of vitamin C? The evidence doesn’t seem quite strong enough yet for such a recommendation.

For instance, the National Institutes of Health notes that long-term intakes of vitamin C above the advised upper intake level of 2 g a day may increase the risk of negative health effects. Excessive amounts of C can cause diarrhoea, abdominal cramps, and nausea, they say.

Also, keep in mind that taking vitamin C regularly might shorten the time you struggle with a cold, but it may not prevent colds altogether, the recent study notes. The vitamin appeared to have a preventive effect only for very active people, like marathon runners and military personnel in training.

But, the researchers said in the study, there is no justification for “ordinary people” to take vitamin C regularly to prevent colds.

So if you come down with a cold and would like to give vitamin C a shot, it’s best to check with your doctor to see if taking those higher dosages—even for a short amount of time—is right for you.