garlic
by Jenny Bryan
Slaves building the Great Pyramid in Egypt are said to have gone on strike when their garlic ration was cut. But history does not record whether that was because they were worried about their cholesterol, blood pressure, bowel problems, infections or one of the many other conditions for which people take garlic today.
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A member of the same family as onions, chives and leeks, Allium sativum was called 'stinking rose' by the Greeks, but is now eaten raw, drunk as syrups and soups, or swallowed as tablets or capsules in an effort to promote good health.
why is garlic good for you?
Garlic contains vitamins A, B1, B2 and C, together with a variety of agents that have anti-microbial, anti-clotting, and cholesterol-changing effects.
People therefore take garlic to prevent colds and flu, to relieve coughs and bronchitis, protect against sickness and diarrhoea and reduce blood pressure and cholesterol levels.
what's the evidence?
Two recent laboratory studies – one from Taiwan, the other from Wolverhampton, demonstrated the anti-microbial effects of garlic oil against throat and stomach bacteria, yeast and fungal organisms. Both groups attributed the effects to the diallyl sulphides contained in the oil.
One of the bacteria against which garlic oil was active was Helicobacter pylori – the microbe which is the main cause of ulcer disease in the stomach and duodenum (see our article on getting to grips with indigestion). However, a two week pilot study of garlic oil capsules (4mg four times a day) in people with proven H. pylori infection, carried out at the Public Health Laboratory in Gloucester, failed to show any effect on the bacterium. The researchers felt that the dose of garlic oil may not have been high enough and suggested further research combining garlic oil with a proton pump inhibitor (PPI) drug to reduce stomach acid, since conventional ulcer treatment uses an antibiotic and a PPI.
Results of a recent clinical trial of an allicin-containing garlic supplement in preventing colds and flu, carried out at the Garlic Centre in Battle, Sussex, were more promising. Volunteers who took a garlic capsule each day for 12 weeks during the winter months had fewer colds and recovered more quickly than those who took a placebo.
garlic and heart disease
A number of studies have investigated the effects of garlic on heart and circulatory problems but they have often been difficult to interpret because of design problems and uncertainties over the way that patients were assigned to different treatments.
Several studies have shown that garlic reduces cholesterol levels. An analysis of results from 16 studies, carried out by researchers at the Universities of Oxford and South Australia in 1994, showed that garlic reduced cholesterol levels by about 12% compared with placebo. A similar analysis, by the same team, of garlic and blood pressure showed an average reduction of systolic and diastolic blood pressures of 7.7 and 5 mm Hg respectively.
A more recent US review of 37 trials confirmed that garlic reduced cholesterol levels in the short term (one to three months) but similar effects were not seen in eight trials when treatment was continued for six months. Small but statistically insignificant effects of garlic were reported in 27 blood pressure trials, though promising results were obtained in anti-blood clotting studies of garlic.
A further large study of the effects of garlic extract on heart attacks failed to show any benefit and results of studies in people with arterial disease in their legs have been mixed.
garlic and cancer
People who are high consumers of raw and/or cooked garlic in their diet have a lower than average risk of stomach and bowel cancers, according to an analysis of trials from around the world, published in the American Journal of Clinical Nutrition. The average difference between low and high garlic eaters was 16g/week and the highest consumers got through around 30g/week. Bowel cancer was reduced by 31% and stomach cancer by 47% in those who ate the most garlic, but the researchers did stress that it wasn't possible to separate the beneficial effects of garlic from other dietary 'goodies', such as vegetables, which are also associated with a low risk of bowel cancer.
A second analysis, carried out by the same US group, which looked at garlic and cholesterol and blood pressure levels, concluded that, while some studies have suggested a protective effect of garlic against cancer, the evidence falls well short of proof.
what about the drawbacks?
The main concern about garlic (if you ignore its effect on personal hygiene) is focused on its anti-blood clotting properties, especially in people who are already taking blood-thinning drugs such as warfarin. Garlic has been implicated in post operative bleeding, and changes in blood clotting ability have been seen when garlic and warfarin are used together.
Anyone taking blood thinning drugs should therefore discuss any possible risks of garlic with their doctor if they want to use more than the occasional clove in their cooking, and US researchers recently proposed that garlic should not be consumed for at least seven days before surgery.
which type to choose
Little research has investigated whether garlic is more beneficial in its natural state or when taken as tablets or capsules. Those who take tablets or capsules are sometimes advised to buy enteric coated products to protect the garlic from stomach acid, so that it can be absorbed more effectively from the intestines.
help and info
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organisations
The Garlic Information Centre
Saberdene House
Church Road
Catsfield
Battle TN33 9DP
Tel: 01424 892440 (Mon-Fri 9am-5pm)
E-mail: garlic@mistral.co.uk
Website: www.garlic.mistral.co.uk
An international information service on the medicinal benefits of garlic. For further information please e-mail or write for a free garlic fact pack. Comprehensive website contains in-depth information about the health benefits of garlic, and details of garlic research and publications.
websites
GarlicWorld
www.garlicworld.co.uk
This site is dedicated to those growing garlic, and so has information for gardeners and farmers. However it also has a useful list of garlic-related books, on subjects such as cookery and health.
Gourmet Garlic Gardens
www.gourmetgarlicgardens.com
This American-based online garlic shop features information about garlic and its health benefits, different varieties of garlic, growing tips and recipes.
reading
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Garlic by Karen Evennett (Sheldon Press, 1998) |
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Garlic by Stephen Fulder and John Blackwood (Healing Arts Press, 2000) |
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The Garlic Lovers' Cookbook complied by the Gilroy Garlic Festival (Celestial Arts, 2003) |
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(February 2002, updated March 2005)
