Scientists talked about the benefits of vitamin C for the body
Vitamin C is involved in the formation of collagen, helps the body absorb iron, supports the immune system and protects cells from oxidative stress. During the cold season, many people start taking ascorbic acid supplements, hoping to use it to prevent the disease or to cope with the symptoms faster. However, scientific evidence shows that vitamin C's capabilities are much more modest than its reputation. About the benefits of vitamin C, how much it is needed by the body, whether it helps with colds and what are the dangers of high doses — in the material "Izvestia".
What is useful for vitamin C and why does the body need it?
Vitamin C, or ascorbic acid, refers to water-soluble vitamins. The human body cannot produce enough of it on its own, so the substance must be supplied regularly with food.
Another important function is antioxidant protection. Ascorbic acid helps neutralize free radicals, active molecules whose excess can damage cells.
Vitamin C is also involved in the immune system. It accumulates in some immune cells and is involved in their response to pathogens. However, the mere involvement of the substance in immune processes does not mean that large doses of the supplement are able to prevent viral infections.
The physiological requirement of an adult is about 100 mg of vitamin C per day. Its main sources are rosehip, sweet pepper, black currant, sea buckthorn, cabbage, greens, tomatoes, potatoes, apples, citrus fruits and other vegetables, fruits and berries.
With a full and varied diet, a healthy person can usually get the necessary amount of vitamin from foods. Additional intake may be required for confirmed deficiency, malabsorption, and some other conditions, but this is not equivalent to using gram doses to prevent colds.
How Vitamin C became a Popular Cold Remedy
The idea of the medicinal properties of vitamin C became widely known thanks to the American chemist Linus Pauling. He was one of the most influential scientists of the 20th century and won two Nobel Prizes.
In 1970, the scientist published the book "Vitamin C and the Common Cold," in which he recommended taking about 1-2 thousand mg of ascorbic acid daily to maintain health and even more to prevent colds. The book became widely known and contributed to the growth of sales of supplements.
Pauling's findings were based on a small number of early placebo-controlled studies, including a trial involving children at a ski camp in the Swiss Alps. Subsequently, his approach was criticized for using work of limited quality, controversial calculations, and an overly broad interpretation of the results obtained in specific groups.
At the same time, the scientific dispute cannot be reduced to the conclusion that Pauling was completely wrong. Recent studies have indeed found a small effect of vitamin C on the duration and severity of colds. The problem was rather the scale of the promises: moderate effects on individual symptoms turned into the idea of ascorbic acid as an almost universal protection against seasonal infections.
What the new research review showed
In January 2025, experts from the University of Helsinki and the Australian National University published in the Polish Archives of Internal Medicine a review of vitamin C research in colds, pneumonia and other respiratory infections.
The authors updated the search for scientific papers and concluded that taking more than 1 g of vitamin C per day does not prevent colds in the general population. A different picture was observed in five trials involving people who experienced short-term heavy physical activity: among athletes and military personnel, the incidence of colds decreased by about half.
In addition, the authors confirmed that regular intake of vitamin C can reduce the severity of the disease. According to the combined test data, the severity of symptoms decreased by about 15%.
However, the 2025 review is not a new clinical trial. The authors reanalyzed the accumulated information, much of which was obtained several decades ago. No new participants were recruited specifically for this work.
In February 2026, the same experts published a critical commentary in the British Journal of Nutrition on the current UK vitamin C intake standards. They pointed out that the British recommendation of 40 mg per day was formed primarily to prevent scurvy and may not take into account other physiological effects of the substance.
At the same time, the 2026 work was also not a new test of vitamin C for colds. The authors relied mainly on controlled studies conducted before 1991, as well as a 1993 trial among ultramarathoners. Therefore, the publication continues the scientific discussion about consumption standards, but does not prove that an ordinary person needs high doses of supplements.
Can vitamin C shorten the duration of illness
Although vitamin C does not prevent most colds, its regular use can slightly shorten the duration of symptoms. The Cochrane Review analyzed 31 comparisons and 9,745 episodes of colds. Among adults who regularly took vitamin C, the duration of the disease decreased by an average of 8%, among children — by 14%.
However, we are talking about the constant intake of supplements even before the onset of the disease. If a person started taking vitamin C only after the appearance of a runny nose, sore throat and other symptoms, there was no sustained effect.
In seven comparisons covering more than 3.2 thousand episodes of colds, vitamin intake after the onset of the disease had no consistent effect on the duration or severity of symptoms. At the same time, the authors of the review noted that there were relatively few such therapeutic trials, so the issue cannot be considered definitively closed.
A more recent meta-analysis in 2023 included 15 comparisons from ten double-blind, placebo-controlled trials. Their participants regularly took at least 1 g of vitamin C per day. Compared with placebo, vitamin C reduced the severity of severe cold symptoms by about 15%. At the same time, the duration of mild manifestations did not change significantly.
To assess the severity, the researchers used different indicators: the duration of the most pronounced symptoms, days spent at home, missing work or school, as well as special scales of well-being. The differences between these techniques limit the accuracy of the overall result.
Even a statistically significant effect remains small from a practical point of view. Reducing the duration of severe symptoms by about 10% may mean a gain of a few hours, rather than a reduction in the disease for several days.
Do I need to take vitamin C after the symptoms appear
The positions of scientists on the therapeutic use of vitamin C differ. The Cochrane review found no sustained effect from starting the drug after the onset of symptoms.
The authors of the 2025 review take a less categorical position. They referred to several old trials in which taking 6-8 grams of vitamin C per day reduced the duration of a cold more than doses of 3-4 g. On this basis, the researchers assumed that the patient could individually check the effect of the supplement at an early start.
However, this recommendation remains controversial. It is based on a small number of long-standing studies, and the suggested doses are several times higher than the current upper intake levels. The effectiveness and safety of self-administration of 6-8 g of vitamin C per day has not been confirmed by modern large-scale trials.
Therefore, this data cannot be taken as a medical recommendation. Vitamin C is not considered a standard treatment for colds and does not replace symptomatic therapy, diagnosis, or medical treatment when the condition worsens.
What are the dangers of high doses of vitamin C
Vitamin C has a relatively low toxicity, but its excess can cause undesirable reactions. The most common are diarrhea, nausea, cramps and abdominal pain, bloating and other disorders of the gastrointestinal tract.
High doses can increase the excretion of oxalates in the urine. The results of studies on the direct connection of supplements with the formation of kidney stones remain ambiguous, but increased caution is necessary for people with kidney disease and impaired metabolism of oxalic acid.
Ascorbic acid also enhances the absorption of non-heme iron. For most healthy people, this is not dangerous, but with hereditary hemochromatosis, prolonged high-dose intake can increase iron accumulation and tissue damage.
Special care is necessary in the treatment of oncological diseases. Data on the combination of antioxidant supplements with chemotherapy and radiation therapy are contradictory. Patients should not start taking high doses of vitamin C without consulting an oncologist.
The risk of side effects depends on the dose, duration of administration, kidney condition, metabolic characteristics and medications that a person receives. Therefore, the idea that a water-soluble vitamin can be taken in any amount is erroneous.
Who may need supplements
Additional vitamin C may be necessary in cases of confirmed deficiency, extremely limited diet, malabsorption, and certain chronic diseases. A higher need is also possible for smokers, as exposure to tobacco smoke increases oxidative processes.
The decision to take a supplement in such cases should take into account the diet, health status and other sources of the vitamin. It is not enough to focus solely on the cold season or advertising promises on your own.
For most healthy people, the main task is not to find the highest possible dose, but to regularly get vitamin C from a variety of foods. The supplement can make up for the deficiency, but it does not turn into a universal remedy for viral infections.
Is it worth drinking vitamin C for colds?
Vitamin C is essential for the body, but adequate intake and megadoses against colds are not the same thing. Studies do not confirm that the supplement is able to reliably protect most people from the disease.
Regular intake may slightly reduce the duration or severity of symptoms, especially with high physical activity and in individual groups. However, the expected effect remains moderate and does not manifest itself in everyone.
Starting treatment after a runny nose, cough, or sore throat has an even less convincing evidence base. The use of 6-8 grams per day remains a controversial research hypothesis and not a recognized treatment option.
Therefore, vitamin C should not be considered either a panacea or a completely useless substance. It performs important physiological functions, and its deficiency requires correction. But adequate nutrition, sleep, hygiene, and timely medical care are much more important to protect against colds.
Переведено сервисом «Яндекс Переводчик»
