Can garlic prevent colds?

More evidence required: scientists hesitate to endorse garlic as a cold fighter on the basis of a single study. Photo: iStock
More evidence required: scientists hesitate to endorse garlic as a cold fighter on the basis of a single study. Photo: iStock

Ancient Egyptians believed garlic could ward off evil spirits. Europeans living in the Middle Ages thought it could deter vampires, but can the bulbous plant thwart a modern demon – the common cold?

Earlier this year I wrote about the cocktail of natural remedies my mother prescribed daily to prevent a sore throat and sniffles – vitamin C, echinacea and thin slices of garlic, swallowed whole.

My review of the latest scientific evidence found no conclusive proof vitamin C was effective at preventing or treating the large range of viruses that we collectively call a cold. Sorry mum. (Although there was some research that suggested active people could reduce the length of their cold with regular vitamin C consumption.)

Fortunately, the evidence for garlic's therapeutic effects are a little more positive.

An analysis by the evidence-based medicine proponent, the Cochrane Collaboration, found only one small study (of 146 people) that was robust enough to include in a review.

It reported that participants who took a garlic tablet every day for three months had fewer colds than the participants prescribed a placebo.

The length of a garlic-taker's cold was also slightly shorter than the people who did not consume the plant, the 2012 review found.

But the authors were quick to caution that one study does not provide enough evidence to warrant buying a winter's worth of garlic tablets. As is often the case with alternative or herbal medicines, more randomised control trials are needed to investigate the plant.

But the benefits of garlic to treat other conditions such as high blood pressure are also being researched by scientists.

A small study published in the European Journal of Clinical Nutrition earlier this year found a daily dose of two pills containing high-potency aged garlic extract could help lower blood pressure.

It's thought garlic can stimulate nitric oxide in cells, which dilates blood vessels and reduces blood pressure. The head of the study, University of Adelaide researcher Karin Ried, says garlic may have more than one mechanism for lowering blood pressure, which could make it a superior treatment over others though about one-quarter of the participants reported side effects such as bloating, gas and a noticeable garlic taste.

A Cochrane review of garlic hypertension treatment found some supporting evidence for its role in lowering blood pressure, but as with the review of its cold prevention properties there was not enough evidence to determine its medicinal benefit.

This story Can garlic prevent colds? first appeared on The Sydney Morning Herald.