With the onset of winter, calls increase for taking large doses of vitamin C to prevent colds and flu, while pharmacies promote its supplements as a way to boost immunity.
But where did this idea come from? And do you really need to take large doses of vitamin C during the cold season?
The belief in the benefits of high doses of vitamin C is associated with the American scientist Linus Pauling, winner of the Nobel Prizes in Chemistry and Peace.
In 1970, Pauling published a book on vitamin C and colds, in which he advocated taking between 1000 and 2000 mg daily to maintain health, and larger doses to prevent colds.
Although Pauling was not a doctor or a specialist in nutrition and infectious diseases, his book contributed to increasing the popularity of vitamin C supplements and establishing the idea that taking large amounts of it may protect us from colds.
However, his conclusions were later criticized due to problems in analyzing the results of the studies he relied on, in addition to the low quality of some of the experiments he depended on.
Subsequent scientific evidence indicates that the effect of vitamin C on colds is limited, and there is no evidence that it prevents them in the general population.
A meta-analysis published in 2023 showed the results of 10 trials involving 2,736 adults, children, and athletes who regularly consumed at least 1,000 mg of vitamin C daily.
The researchers found that taking vitamin C was associated with a reduction in the severity of cold symptoms by about 15%, but its effect on the duration of symptoms was limited.
A meta-analysis published in 2013 also showed that taking about 200 mg daily does not reduce the number of colds in the general population, with a greater benefit observed in certain groups who are subjected to intense physical exertion, such as athletes and military personnel.
Overall, the results suggest that regular vitamin C intake may reduce the severity of symptoms in some individuals to a limited extent, but it does not prevent colds. Furthermore, taking it after symptoms have already appeared does not seem to be beneficial.
Most people need relatively small amounts of vitamin C, which can be easily obtained from food. In Australia, the recommended daily intake for adults is 45 mg, an amount that can be obtained from half an orange, a small portion of broccoli, or orange juice.
Conversely, taking more than 1000 mg daily on an ongoing basis may lead to side effects such as diarrhea, nausea, stomach cramps and bloating, and may also increase the risk of kidney stones in some people.
Excessive intake may also lead to increased iron absorption in people with hemochromatosis, and it can interfere with some treatments and medications.
Scientific evidence does not support the idea that high doses of vitamin C prevent colds. While taking it regularly may offer limited benefit in reducing the severity or duration of symptoms for some people, taking it when symptoms appear is of little use.
Therefore, there is no need to stockpile large quantities of vitamin C supplements in preparation for winter. For most people, it is sufficient to obtain the body's needs through a balanced diet rich in fruits and vegetables.
Those considering taking high doses of supplements should consult a doctor, especially if they have chronic illnesses or use medications regularly.
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