Those who start eating lemons at first symptoms of the common cold should slow down. According to a recent study, Vitamin C does nothing to prevent the common cold.

Australian and Finnish researchers after analysis of 55 studies say that the only effect that Vitamin C can have is to shorten the duration of a cold. Some 30 studies noted that 8% of adults and 13% of children who continued to take Vitamin C while they had a cold cut short its duration.

Nobel Prize-winning chemist Linus Pauling in his 1970s book, "Vitamin C and the Common Cold," sparked interest in the supplement that has grown to a more than $600 million annual business in Britain, the Times of London reported.

However, the study has shown that people who took up to 2 grams of Vitamin C daily caught colds at the same rate as people who took a placebo. The study was conducted by researchers Robert Douglas of Australian National University, Canberra, and Harri Hemila of the University of Helsinki. In order to assess whether supplemental vitamin C can reduce the risk of picking up a cold, the authors focused on 23 studies done in the general population, using doses of up to 2g daily. The result of the study "throws doubt on the utility of this wide practice," the researchers said in the journal Public Library of Science Medicine.

Nevertheless, one study found that very large doses of Vitamin C - 8 grams - taken on the first day of a cold appeared could shorten the disease itself. The authors say that the clinical significance of this minor reduction "is questionable, although the consistency of these findings points to a genuine biological effect."

But the authors did find evidence that the vitamin could help prevent colds in people exposed to extreme physical exertion or cold weather. They found six studies in which the vitamin or a placebo was given to marathon runners, skiers and soldiers exposed to significant cold and/or physical stress.

Those taking the vitamin experienced, on average, a 50 per cent reduction in common cold incidence. The authors urge "great caution", though, in making generalisations from this finding in 6 studies that is mainly based on marathon runners.

Several years ago researchers discovered that big doses of vitamin C can be dangerous for smokers.

Cigarettes and vitamin C are incompatible: big doses of this vitamin could be dangerous for smokers. According to Australian scientists, while smoking heavy metal cadmium penetrates into human organism. Big amounts of this metal could be found in wheat, in Crustacea and in rice imported from Asia. Usually vitamin C protects human organism from tumours due to its anti-oxidant effect. Though, as Australian scientists found out, in combination with cadmium the vitamin could provoke appearing cancer cells. Doses over 4 gram a day are dangerous for smokers. Cadmium could be contained in human organism for tens of years and it is very complicated to be removed. That is why not only todays smoking or consuming bad food is dangerous, but even bad habits and infected food one used 10 years ago. The scientists state cadmium can penetrate to nature from batteries, smelting furnaces, dye stuffs and plastics.