BMJ Group Medical Reference
Your body needs some vitamin C to work properly. You get this vitamin from fruits and vegetables, such as oranges, grapefruits, and broccoli. You can also buy vitamin tablets that contain vitamin C. Some people think that taking extra vitamin C might help with a cold.
But there's good research to show that taking high doses of vitamin C is unlikely to help you recover from a cold.
A summary of the research (a systematic review) found that colds lasted just as long for people who took up to 4 grams (0.14 ounces) a day of vitamin C. People who took vitamin C had symptoms that were just as severe as people who took a dummy treatment (a placebo).
Some people take vitamin C to try to prevent colds. We haven't looked closely at the research on this, so we don't know whether it works.
The research didn't mention any side effects of taking vitamin C for a cold. In studies of people taking vitamin C every day to prevent colds, no one had any serious problems.
A placebo is a 'pretend' or dummy treatment that contains no active substances. A placebo is often given to half the people taking part in medical research trials, for comparison with the 'real' treatment. It is made to look and taste identical to the drug treatment being tested, so that people in the studies do not know if they are getting the placebo or the 'real' treatment. Researchers often talk about the 'placebo effect'. This is where patients feel better after having a placebo treatment because they expect to feel better. Tests may indicate that they actually are better. In the same way, people can also get side effects after having a placebo treatment. Drug treatments can also have a 'placebo effect'. This is why, to get a true picture of how well a drug works, it is important to compare it against a placebo treatment.
A systematic review is a thorough look through published research on a particular topic. Only studies that have been carried out to a high standard are included. A systematic review may or may not include a meta-analysis, which is when the results from individual studies are put together.
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