Prevention is always better cure, although despite many years of research, and despite popular belief, Vitamin C will not prevent a cold. However more recent research is now suggesting that Vitamin C and Zinc may have important roles in reducing the symptoms of the common cold.

Firstly, let's look at Vitamin C
Ever the controversial nutrient since Linus Pauling in 1970 claimed that Vitamin C prevents and alleviates the common cold. Since his conclusions, much more work on Vitamin C has been carried out, with trials that have been better designed.

A recent review (from the Cochrane Database of Sytematic Reviews) set out to 
ask 2 questions:

(1) Does regular high dose Vitamin C supplementation reduce the incidence of colds? i.e. does it prevent colds?

(2) Does taking Vitamin C in high doses at the onset of a cold have a therapeutic effect? i.e. when you've got a cold, can you get rid of it more quickly?

The reviewer's looked at 30 trials highlighted in 2 other reviews done in 1989 and 1992. They concluded that long term daily supplementation with Vitamin C in large doses does not appear to prevent colds. However, "there appears to be a modest benefit in reducing the duration of cold symptoms from ingestion of relatively high doses of Vitamin C." The actual dose needs to be studied further, but studies typically gave 1-2g of Vitamin C a day (spread through the day) during a common cold.

What is clear is that this area is still grey, but that the dose to treat symptoms is high ­ much higher than what you would typically get naturally from food and so is a 'medicinal dose'. It is know that at 2g or more, Vitamin C can cause diarrhoea as well as other side effects, which is why you should stop taking the high dose supplement when your symptoms go.

Douglas RM, Chalker EB, Treacy B. Vitamin C for preventing and treating the common cold (review), Cochrane Database of Systematic Reviews (computer file). (2):CD000980, 2000

Now Zinc
In a study published this year in the Annals of Internal Medicine, workers recruited 48 people within 24hours of developing symptoms of the common cold. 25 of these people took a zinc lozenge containing 12.8mg of Zinc Acetate every 2-3 hours while awake for as long as they had cold symptoms and rated their symptoms daily e.g. sore throast, nasal discharge, nasal congestion, sneezing, cough, scratchy throat, hoarseness, muscle ache, fever and headache. 23 people took a placebo pill and subjectively recorded their daily symptoms. The trial was a randomised, double-blind, placebo-controlled trial.

The results were interesting. Taking the zinc lozenges was associated with reduced duration and severity of the cold symptoms, especially cough, which showed a shorter mean duration time of 3.1 days with zinc compared with 6.3 days without.

However other critical reviews of the effects of zinc have been less convincing, so much so that a Cochrane Systmatic Review of this topic in 2000 concluded that "overall, the results suggest that treatment with zinc lozenges did not reduce the duration of cold symptoms." But a review of clinical trials in 1998 concluded that there was "fair evidence" for zinc treating the common cold.

It may be that it depends on how, when and in what form the zinc is taken as suggested in the 1998 review article.

It is important to start taking the therapeutic zinc within 48 hours and suck the lozenges every 2-3 hours while awake. The therapeutic dose may be a minimum of approximately 13mg zinc per lozenge. It is also suggested that ingredients such as citric acid, sorbitol and mannitol may bind free zinc ion, which may be the reason why results in studies have been so variable. Many of the over the counter zinc lozenges currently available contain far less than the therapeutic doses used in the succesfull trials.

Prasad AS, Fitzgerald JT, Bao B, Beck FW, Chandrasekar PH. Duration of symptoms and plasma cytokine levels in patients with the common cold treated with zinc acetate. A randomised, double-blind, placebo-controlled trial. Ann Intern Med. 133 (4):245-252, 2000 Aug 15