Garlic is widely used in health supplements, often in the belief it can help prevent virus infections like the common cold and flu, arterial disease, and other ills, including cancer. None of these claims have been substantiated by well-conducted, randomized, controlled clinical trials. However, there is weak evidence that garlic can prevent the common cold. The Cochrane Library has reviewed clinical trials published in the medical literature, and found only five that were potentially relevant; only one of these met the criteria set for evaluating effectiveness.
There were 146 volunteers in the study; they were randomly assigned to take a garlic supplement (with 180 mg allicilin) or a placebo, daily for 12 weeks. During that period they were to report if they had a cold, the duration of illness, and time away from work.
There were 24 common colds among the garlic takers, and 65 among the placebo group. This was a statistically-significant difference. The duration of illness was similar in both groups – 4.63 days vs. 5.63 days, a not-significant difference. The only adverse effects of garlic reported were rash and odor.
On average, children have 6-8 colds a year, and adults have 2 to 4. (As someone in their late 70s, I get fewer than one common cold a year – a bonus for getting old!) The ‘frequencies’ of colds in these groups of 73 persons each was 1.3 a year for the garlic-takers and 3.5 a year for the placebo. It looks as if they used a ‘young adult’ population.
Garlic has many useful properties – especially in the kitchen. It may be that generous intake can help you prevent a cold, even if it won’t shorten the illness of make you feel better while you’re sick. But that’s what chicken soup is for.