Garlic (Allium sativum) is an important part of the Mediterranean diet, and is such a popular culinary herb that average consumption, worldwide, is equivalent to one clove per person per day.

Garlic is a source of a powerful antioxidant called allicin. Allicin is not present in whole garlic cloves, but is formed from alliin, an odourless amino acid unique to the garlic family. Alliin is stored within garlic cells, separated from the enzyme (alliinase) that breaks it down. Cutting or crushing a garlic clove brings alliin and alliinase together to produce diallyl thiosulphinate, which provides the characteristic, pungent odour. Sulphur compounds formed from the breakdown of allicin also have beneficial, medicinal effects.

Garlic lowers cholesterol>

Allicin protects ‘bad’ LDL-cholesterol from oxidation, reducing its uptake by scavenger cells to protect against atherosclerosis. Garlic also reduces cholesterol production in the liver and hastens excretion of fatty acids into bile. Data from 39 clinical trials show that garlic can reduce total serum cholesterol by an average of 17 mg/dL (0.44 mmol/L), and reduced LDL-cholesterol by 9mg/dL (0.23 mmol/L) in those with elevated cholesterol levels, provided garlic was used for longer than 2 months. This is a significant finding, as an 8% reduction in total serum cholesterol is associated with a 38% reduction in risk of heart attack in middle-aged adults.

Garlic improves the circulation

Taking garlic supplements helps to dilate small arteries (arterioles) and (venules) to improve blood perfusion in the skin and nail folds by as much as 55 per cent. This ‘warming’ effect is helpful for people with poor peripheral circulation and for helping to improve the strength of brittle nails. Garlic extracts have also been found to reduce age-related stiffening of the aorta, and increase its elasticity so the heart has to work less hard to pump blood through the circulation.

Garlic reduces blood stickiness

The sulphur compounds in garlic help to relax blood vessels and reduce platelet stickiness to reduce the formation of unwanted blood clots. Some of the ingredients in garlic (ajoene, methylallyl trisulphide and dimethyl trisulphide) are as powerful as aspirin in reducing platelet clumping. These effects are seen after eating the equivalent of half a clove of garlic and lasts for around three hours.

Garlic lowers blood pressure

The beneficial effects of garlic on cholesterol, blood vessel dilation and blood stickiness might be expected to help lower blood pressure. Different trials have shown different results, with some showing that taking garlic can reduce blood pressure by an average of 16.3/9.3 mmHg in people with hypertension. Other studies that mainly involved people without an elevated systolic blood pressure have not shown benefit, however. The latest analysis, which includes data from ten randomised controlled trials, suggests that garlic extracts can reduce blood pressure by an average of 4.4/2.68 mmHg compared with controls. This may seem small, but it is a significant result comparable to that achieved with prescribed diuretic drugs.

Garlic may prevent colds

Garlic has antimicrobial actions and is a popular remedy to help keep viral colds at bay. A Cochrane systematic review of clinical evidence in 2014 found one eligible trial involving 146 people who took either garlic supplements or inactive placebo for 12 weeks. Only 24 of those taking garlic developed a cold, compared with 65 of those on dummy tablets. On average those taking garlic had colds lasting 1.5 days while those taking a placebo had colds lasting 5 days. However, as only one trial met the inclusion criteria, the authors stated there was insufficient evidence to draw robust conclusions regarding the effects of garlic in preventing or treating the common cold.

Using garlic in cooking

If garlic is cooked immediately after peeling, allinase is inactivated and some of its beneficial effects are lost. When using garlic in recipes, crush it, then wait five minutes until adding it to the pan. Ideally, add garlic towards the end of cooking for optimum pungency and medicinal benefits. Scientists have found that drinking milk (full fat or fat-free) after eating garlic can reduce mouth odour.

Garlic dose

The usual dose for supplements is 600–900 mg standardized garlic powder tablets a day.

Garlic safety

A recent paper confirmed there are no harmful interactions when taking garlic with blood pressure lowering or blood-thinning medication, but as always check with your doctor if you are on prescribed drugs.

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