Can extra vitamin C help treat a cold?
Vitamin C has been sold as a cold remedy for decades, but a review of 29 studies found no convincing evidence that taking vitamin C supplements regularly prevents colds.
There is some evidence that it might slightly reduce the duration of a cold, but only by around 8%. So for a cold that lasts a week, that’s around half a day.
People who seemed to benefit more from supplements were those under extreme physical stress, like marathon runners or those training in cold temperatures. In these cases, taking a vitamin C supplement two to three weeks before the intense training exercise reduced the risk of developing a cold by half.
Taking more than 1,000mg (one gram) a day of vitamin C has been linked with diarrhoea and stomach cramps. At doses above one gram, absorption also falls to less than 50%, and anything your body doesn’t absorb is flushed out in urine, so mega doses offer little benefit.
Originally published October 2025
Laura Tilt is a registered dietitian with a master’s in public health nutrition and a postgraduate diploma in dietetics. Since qualifying in 2012, she has specialised in gastroenterology at London’s UCLH before moving into freelance practice. With over 10 years of experience translating nutrition science into accessible, meaningful advice, Laura’s specialist interests include digestive health, disordered eating, and sports nutrition.
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