Garlic has been widely used as both food and medicine since ancient times, adding its unique flavour to dishes all over the world and its healing properties to numerous natural remedies.
Today, garlic is a popular dietary supplement used to lower cholesterol and keep the heart healthy as well as to fight against cancer, diabetes, dementia and more. In some countries, the sale of garlic preparations ranks with those of the leading prescription drugs (Phytother Res, 2003; 17: 97-106).
But is garlic really a cure for all manner of ills?
Garlic is best known as a heart-healthy supplement and there are lots of studies to back this up. In a review by the prestigious Cochrane Collaboration, garlic significantly lowered blood pressure compared with a placebo-with no serious side-effects (Cochrane Database Syst Rev, 2012; 8: CD007653). It can also boost 'good' cholesterol (high-density lipoprotein, or HDL) while slashing levels of 'bad' cholesterol (low-density lipoprotein, or LDL)-at least in a study with rats (Lipids Health Dis, 2012; 11: 77). In people, the evidence
for cholesterol is somewhat mixed. One review said that the supplement could reduce total cholesterol and triglycerides (another type of fat in the blood), but had no effect on the HDL-to-LDL ratio (J Sci Food Agric, 2012; 92: 1892-902).
Other evidence shows that garlic has antiplatelet or anticlotting activity, which means that it may be useful for preventing thrombosis-blood clots inside a blood vessel. Over the long term (300 mg daily of standardized garlic powder for more than two years), it improved the elasticity of the aorta-the largest artery in the body-so helping to maintain optimal blood pressure (ISRN Cardiol, 2011; 2011: 397136).
What this all adds up to is that garlic may be a beneficial supplement for preventing heart disease
or at least perhaps treating it in its early stages. And sure enough, one study that looked at the impact of taking 80 mg/day of aged garlic extract for 12 weeks found that it reduced several cardiovascular risk factors among postmenopausal women, including body mass index (BMI), LDL cholesterol and levels of homocysteine-a type of amino acid produced in the body as a byproduct of meat consumption-which may be a better predictor of heart disease than cholesterol (Nutr Res Pract, 2012; 6: 226-31).
Cancer prevention is another touted benefit of garlic, but the findings are mixed. A study in Iowa looked at the diets of over 40,000 women and found that those who ate the most garlic had the lowest risk of colon cancer (Am J Epidemiol, 1994; 139: 1-15). In a Chinese study of people with a high incidence of stomach cancer, those who ate the most garlic had a 40-per-cent lower cancer risk than those who ate the least amounts of garlic (J Natl Cancer Inst, 1989; 81: 162-4).
However, a 10-year Dutch study of more than 120,000 people found no link between garlic supplements and breast, colon, rectal or lung cancer prevention (Carcinogenesis, 1996; 17: 477-84). It may be that it's fresh garlic, rather than the pill forms, that provides the most effective anticancer protection.
Still, several forms of garlic (such as powders and extracts) have shown anticancer activity in the lab (Carcinogenesis, 1993; 14: 1627-31). Also, components of aged garlic blocked carcinogens and prevented cancers of the oesophagus, colon, lung, breast, prostate and stomach (Nutr Cancer, 1997; 27: 186-91; Nutr Rev, 1996; 54: S82-6). More recently, garlic oil was able to protect against chemically induced hepatocar-cinoma-the most common type of liver cancer. In
a Japanese study of 50 people with inoperable colorectal, liver or pancreatic cancer, their immune activity improved after taking aged garlic extract for 6 months (J Nutr, 2006; 136 [3 Suppl]: 816S-20S).
Besides heart disease and cancer, garlic may be useful for a variety of other illnesses, the evidence suggests.
People with type 2 diabetes could benefit from garlic supplements, according to a joint study by researchers at the University of Karachi, Pakistan, and King's Hospital, London. A total of 210 type 2 diabetes patients were given either garlic tablets (at doses of either 300, 600, 900, 1200 or 1500 mg per day), the diabetes drug metformin or a placebo for 24 weeks.
The patients given the garlic tablets all saw a significant reduction in their fasting blood sugar levels compared with the placebo-and the higher the dose, the better the effect.
"Garlic is more effective than placebo and comparable to metformin in reducing fasting blood glucose and may be a valuable addition in the management of diabetic patients," the researchers concluded (J Med Plant Res, 2011; 5: 2922-8).
The common cold.
Some studies suggest that taking garlic supplements might be a good way to fight off colds and flu. In a UK trial of 146 volunteers, one capsule per day of garlic (containing 180 mg of allicin-the ingredient thought to be responsible for much of garlic's beneficial effects) led to 63-per-cent fewer colds and 70-per-cent fewer sick days compared with those taking a placebo. What's more, when participants did catch a cold, the people taking garlic saw their symptoms go away faster than did those who took a placebo (Adv Ther, 2001; 18: 189-93).
Growing laboratory evidence suggests that garlic may be brain-protective, helping to reduce the risk of dementias such as vascular dementia and Alzheimer's disease. Many possible mechanisms could be behind this effect, including the inhibition of inflammation, reduction of levels of homocysteine and protection of nerve cells (neurons) against apoptosis (programmed cell suicide triggered by oxidative stress).
Although more research is called for, so far the studies in people have suggested that aged garlic can protect against a wide range of risk factors that are common to cardiovascular disease and dementia (J Nutr, 2006; 136 [3 Suppl]: 810S-2S).
Garlic can sometimes cause side-effects if you take too much of it-such as an upset stomach, bloating, nausea and headaches-but it's listed as 'Generally Recognized as Safe' (GRAS) by the US Food and
Drug Administration (FDA), America's drugs and food products watchdog. A dose of around 200 mg daily-the equivalent of around 70 cloves-is non-toxic.
However, because of its anticlotting properties, garlic supplements should not be taken with blood-thinning drugs such as heparin, warfarin and coumarin derivatives, or before surgery, as this could lead to uncontrollable bleeding. They might interfere with other drugs too, so check with a health professional before taking them.
These small considerations aside, if you can stand the smell, this ancient powerhouse ingredient may be the answer to many modern ills.
What's good about garlic?
Garlic is rich in antioxidant phytochemicals such as organosulphur (suphur-containing) compounds and flavonoids, both capable of scavenging tissue-damaging free radicals (Cancer J, 1990; 3: 20-1). Although the mechanisms behind all of garlic's components are still not known, many of its heart-protective and anticancer effects are thought to be due to these antioxidant actions (Planta Med, 1994; 60: 417-20; Planta Med, 1992; 58: 468-9).
There's been a lot of focus on the allicin content of garlic supplements, as it was once thought that this sulphur-containing compound was the active ingredient behind garlic's beneficial effects. However, experts now believe that no single constituent of garlic is its main active ingredient. Instead, the range of constituents in garlic most likely act in synergy to produce a variety of healthful benefits.
Ajoene, for example, which is formed by combining garlic's allicin and diallyl disulphide, has proven antithrombotic and antibiotic activity. And a number of its other constituents-including 33 identified sulphur compounds and 17 amino acids, as well as germanium, calcium, copper, iron, potassium, magnesium, selenium, zinc, and vitamins A, B1 and C-have known health-making activities in the body (Br J Clin Pharmacol, 1989; 28: 535-44).
This means that it makes sense to go for supplements that are minimally processed (so avoid odourless garlic, for instance, as it's usually been cooked, which can deplete the allicin content) and to eat garlic raw as much as possible.