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Dear Doctor: Can garlic prevent cancer? If so, is it safe for everyone to take dietary supplements

Is it true that garlic can prevent cancer. If so, how much should I take?

Taking garlic, or any other dietary supplement, will not guarantee that you won't get cancer, but garlic does have possible anti-cancer properties. Research has shown that garlic may reduce the risk of developing cancer, especially stomach and colorectal cancer. However, because all garlic preparations are not the same, it is difficult to say the exact amount of garlic that may be needed to reduce your cancer risk. The WHO (World Health Organisation) guidelines for general health promotion for adults is a daily dose of 2-5g of fresh garlic (about one clove), 300-1,000mg of garlic extract, 2-5mg of garlic oil or 0.4-1.2g of dried garlic powder.

What is in garlic that might help prevent cancer?

There are several compounds involved in garlic's possible anti-cancer effects. Garlic contains allyl sulphur and related substances that can slow or prevent the growth of tumour cells. But the chemistry of garlic is complicated. As a result, the quality of garlic products depends on the manufacturing process. Peeling, cutting or crushing raw garlic releases an enzyme called allinase and starts a chemical reaction that produces DADS (diallyl disulphide). But if garlic is cooked immediately after peeling the cancer-fighting benefit of DADS is lost, so wait 15 minutes between peeling and cooking garlic. Don't microwave garlic as this kills the active ingredients.

Can too much garlic be harmful?

Yes, excessive intake of garlic can cause side effects. Be careful about taking garlic if you have stomach ulcers or are prone to digestive irritation. Taking it on an empty stomach may cause heartburn, nausea, vomiting or diarrhoea. Fresh garlic applied to the skin can cause a rash, skin burns or asthma.

Garlic should be stopped before having some surgery or dental procedures due to an increased risk of bleeding. It should not be taken with certain medications such as blood-thinning tablets such as aspirin or warfarin, or non-steroidal anti-inflammatory drugs such as ibuprofen. Bleeding can be a serious side effect of garlic use.

Does garlic have any other health benefits?

It has been reported that garlic can result in small reductions in total cholesterol and 'LDL' (bad cholesterol) over short periods of time (four to 12 weeks), but it's still not clear if these benefits persist. Deposits of cholesterol in blood vessels may not grow as quickly in people who take garlic. It has anti-bacterial and anti-fungal properties. Garlic has 1pc of the potency of penicillin and may help ward off a number of infections such as listeria, E-coli, candida and staphylococcus.