Helen Barratt wonders if vitamin C really does help sort out that all too common illness, the cold

Every winter, at the slightest sign of a sniffle, my mother whips out the "extra strength" vitamin C tablets and stands over us while we take them. She is convinced that they provide all the protection we need from coughs and colds. Any subsequent illnesses are met with a total lack of sympathy because we "obviously were not taking the tablets."

It seems that this belief is not just confined to my mum's generation or our culture: I asked a friend in my year from Singapore whether or not he would take vitamin C for a cold. He nodded seriously and told me that there was little point taking it when I actually had a cold as it would not help the symptoms. Instead, I should take it before I become ill to stop the illness developing.

What is vitamin C?

Vitamin C (ascorbic acid) is one of nine water soluble vitamins required by the body; the current recommended daily amount for a 70 kg man is 60 mg. It is particularly abundant in citrus fruits. A vitamin C deficiency leads to scurvy--a disease causing sore spongy gums, loose teeth, fragile blood vessels, and swollen joints.

Vitamin C has a well documented role in hydroxylation reactions: many of the symptoms of scurvy can be explained by the reduced hydroxylation of collagen resulting in defective connective tissue. Vitamin C is also a well known antioxidant able to inactivate toxic oxygen free radicals which potentially contribute to the development of heart disease and cancer by damaging lipid membranes, proteins, and cellular DNA.¹

Over the past few decades, the properties of vitamin C have led to it being the centre of a number of health claims involving a variety of conditions.

What has vitamin C got to do with colds?

The common cold--usually caused by a rhinovirus--is currently the most frequent illness managed in general practice. Colds afflict most adults two to four times a year, yet despite a long search for a cure only potential treatments for the symptoms have been found.²

In 1970 the American Nobel laureate Dr Linus Pauling claimed that high doses of vitamin C taken regularly could not only halve the incidence of colds but also greatly reduce their severity. He drew his conclusions from an analysis of four previously published trials. His conclusions from this evidence were correct.

It now appears that he was overoptimistic about the extent of the benefit. Pauling based his conclusions on a single trial, with a placebo as control, conducted on schoolchildren in a skiing camp in the Swiss Alps. He found a significant decrease in the incidence and duration of the common cold in the group administered 1 g/day of vitamin C. As children in a skiing camp cannot be regarded as a representative sample of the general population his findings are now considered to have been too bold.³ Since then the role of oral ascorbic acid in preventing and treating colds has remained controversial despite many further trials prompted by Pauling's work.

In 1975 a review concluded that the minor benefits seen were of questionable validity.⁴ However, a more recent analysis of the same review pointed out several errors and suggested that vitamin C could significantly decrease the duration of episodes and the severity of symptoms of the common cold by an average of 23%.⁵

Last year two reviewers from the National Centre for Epidemiology and Population Health in Canberra, Australia, conducted a systematic review for the Cochrane database, which is regarded by many as the gold standard in evidence based medicine.⁶ This included 30 randomised and non-randomised trials of vitamin C taken to prevent or treat the common cold. It aimed to answer the following questions:

• Do regular high doses of vitamin C reduce the incidence of colds?
• Does taking vitamin C in high doses at the onset of a cold have a therapeutic effect?

The conclusion was that taking doses as high as 1g/day of vitamin C over a long period does not prevent colds. Relatively high doses of vitamin C modestly reduce the duration of cold symptoms.

The relation of dose to therapeutic benefit has not been properly explored, but in trials testing the administration of vitamin C after cold symptoms occurred, there was some evidence that a large dose produced greater benefits than lower doses.

Is vitamin C good for colds?

Controversy remains over the role of vitamin C in preventing and treating colds. As there is currently no known cure for a cold, symptoms are treated using a variety of methods ranging from * adrenoceptor agonists to simple steam inhalation, and the exact role of ascorbic acid in this is not yet known.

The authors of the Cochrane review stated, "On the basis of these studies there is a clear case for discouraging the community wide use of regular prophylaxis with high doses of vitamin C."

However, Linus Pauling's influence extends far and wide, not least because of the current interest in pursuing alternative therapies, and the media are happy to continue publicising his ideas regarding vitamin C. As my mum says, "Good Housekeeping says it works, so it must be true."