Q. I have heard so much about the power of garlic to do everything from relieving cold symptoms to lowering cholesterol. Is there anything in these claims? Should I eat more garlic or take supplements, especially with the season for winter colds approaching? I have slightly high cholesterol, which I am trying to control with my diet.

A. The recorded uses for garlic range from giving strength and endurance to the Ancient Egyptians who built the pyramids to protecting against the plague and treating leprosy as well as combating the common cold. Not surprisingly, it has developed rather a “cure-all” reputation.

Modern scientists have attempted to put garlic to the test and hundreds of studies have been carried out, many in the laboratory, many on animals and some on human beings. Yet despite all this work, very little has been proved beyond doubt.

Garlic belongs to the allium family of plants and is related to onions, shallots, chives and leeks. It contains more than 200 phytochemicals - plant chemicals believed to provide health benefits - more than half of which are sulphur-based compounds. The one given most attention is allicin, which is what gives garlic its strong flavour and makes your breath smell.

Chewing or crushing garlic triggers the conversion of another substance, called alliin, into allicin, which is then quickly turned into other compounds such as ajoene. Cooking stops the formation of allicin and other potentially therapeutic chemicals, which suggests that only fresh garlic would be beneficial. That said, there may be many other compounds in the plant that survive cooking and could affect various parts of the body.

The most encouraging research area is the one focusing on garlic's potential ability to lower cholesterol. Some studies suggest that it can reduce “bad” cholesterol by about 10 per cent, although a round-up of research on garlic supplements indicated that, in six out of ten studies, supplements were only “modestly effective” in lowering such cholesterol.

This ability is thought to depend very much on the quality of the supplement and the levels of allicin present. It is probably worth taking a good brand of supplement if you also follow a traditional cholesterol-lowering diet that is low in saturated fats, and try to maintain a normal bodyweight.

Laboratory studies have suggested that garlic extracts help to keep blood cells from clumping together. If this were also to happen when we eat garlic, it could, in theory, reduce our risk of blood clots and heart disease.

There is also some evidence that garlic may help to lower blood pressure, probably by dilating blood vessels a little, thus helping the blood to flow more freely. Recently published research from the University of Adelaide looked at 11 studies in which people were given either a placebo or garlic supplements: it found that those taking the supplements did show significant reductions in blood pressure - in some cases, the effect was similar to that of taking established hypertension drugs.

There will probably never be a “final word” on garlic, but it does appear that allicin can block enzymes that give viruses their ability to flourish. This action may help to explain why some people swear that garlic helps them to keep colds at bay. There is no harm in chomping through a clove of garlic each day, at any rate - and you never know, it may just help to stop you falling prey to every cold doing the rounds this winter.

If you have nutrition questions for Amanda, e-mail her at amandaursell@thetimes.co.uk

You are likely to get most benefit from eating garlic raw, although this can cause indigestion in some people.

If you opt for supplements, look for those with at least 4,000 micrograms of allicin potential per tablet, and take a 400mg-600mg supplement. Kwai garlic is a particularly good brand with a guaranteed allicin yield of 1,800 micrograms per 300mg one-a-day tablet.

Garlic supplements may increase the risk of bleeding if taken with warfarin, aspirin or other drugs that decrease blood clotting, or possibly with fish-oil pills. They may interact with some medications for diabetes, HIV disease, hypertension, cancer and cholesterol. Check with your GP before supplementing with garlic if you take any of these medications.