Garlic : Scientific and Traditional Uses

by MedlinePlus

Numerous controlled trials have examined the effects of oral garlic on serum lipids. Most studies have been small (<100 subjects), with poorly described design and results, and most have reported non-significant modest benefits. Several overlapping meta-analyses have pooled these studies, suggesting that non-enteric-coated tablets containing dehydrated garlic powder (standardized to 1.3% alliin) elicit modest reductions in total cholesterol vs. placebo (<20mg/dL) in the short term (4-12 weeks), with unclear effects after 20 weeks. Small reductions in low-density lipoprotein (LDL) (by <10mg/dL) and triglycerides (by <20mg/dL) may also occur in the short-term, although results have been variable. High-density lipoprotein (HDL) levels are not significantly affected. Long-term effects on lipids or cardiovascular morbidity and mortality remain unknown. Other preparations (such as enteric-coated or raw garlic) have not been well studied.

Small reductions in blood pressure (<10mmHg), inhibition of platelet aggregation, and enhancement of fibrinolytic activity have been reported, and may exert effects on cardiovascular outcomes, although evidence is preliminary in these areas.

Numerous case-control/population-based studies suggest that regular consumption of garlic (particularly unprocessed garlic) may reduce the risk of developing several types of cancer, including gastric and colorectal malignancies. However, prospective controlled trials are lacking.

Multiple cases of bleeding have been associated with garlic use, and caution is warranted in patients at risk of bleeding or prior to some surgical/dental procedures. Garlic does not appear to significantly affect blood glucose levels.

Evidence

These uses have been tested in humans or animals. Safety and effectiveness have not always been proven. Some of these conditions are potentially serious, and should be evaluated by a qualified healthcare provider.

Uses based on scientific evidence

High cholesterol

Multiple studies in humans have reported small reductions in total blood cholesterol and low-density lipoproteins ("bad cholesterol") over short periods of time (4 to 12 weeks). It is not clear if there are benefits after this amount of time. Effects on high-density lipoproteins ("good cholesterol") are not clear. This remains an area of controversy. Well-designed and longer studies are needed in this area.

Anti-fungal (applied to the skin)

Several laboratory studies and historical reports describe the application of garlic to the skin to treat fungal infections, including yeast infections. However, little information on effectiveness is available. Take caution as garlic can cause severe burns and rash when applied to the skin of sensitive individuals.

Anti-platelet effects (blood thinning)

Laboratory and human studies suggest that garlic may reduce blood clotting due to effects on platelets in the blood. Excessive bleeding has been reported in people who take garlic supplements. It is not clear what doses of garlic have these effects, and caution is warranted in people with bleeding problems or taking drugs that increase the risk of bleeding. Additional safety studies are needed.

Atherosclerosis ("hardening" of the arteries)

Preliminary research in humans suggests that deposits of cholesterol in blood vessels may not grow as quickly in people who take garlic. It is not clear if this is due to the ability of garlic to lower cholesterol levels, or to other effects of garlic.

Cancer

Laboratory, animal and preliminary human studies suggest that regular consumption of garlic (particularly unprocessed garlic) may reduce the risk of developing several types of cancer including gastric and colorectal malignancies. Some studies use multi-ingredient products so it is difficult to determine if garlic alone may play a beneficial role. Further well designed human clinical trials are needed to conclude whether eating garlic or taking garlic supplements may prevent or treat cancer.

Familial hypercholesterolemia

Familial hypercholesterolemia is a genetic disorder in which very high cholesterol levels run in families. Research in children with an inherited form of high cholesterol suggests that garlic does not have a large effect in lowering cholesterol levels in these patients.

Heart attack prevention in patients with known heart disease

It is not clear if garlic prevents future heart attacks in people who have already had a heart attack. The effects of garlic on cholesterol levels may be beneficial in such patients.

High blood pressure

Numerous human studies report that garlic can lower blood pressure by a small amount, but larger, well-designed studies are needed to confirm this possible effect.

Peripheral vascular disease (blocked arteries in the legs)

Some human studies suggest that garlic may improve circulation in the legs by a small amount, but this issue remains unclear. Better-designed studies are needed.

Tick repellant

No reliable scientific information is available on using garlic as a tick repellant.

Upper respiratory tract infection

Preliminary reports suggest that garlic may reduce the severity of upper respiratory tract infections. However, this has not been demonstrated in well-designed human studies.

Diabetes

Animal studies suggest that garlic may lower blood sugar and increase the release of insulin, but studies in humans do not confirm this effect. Stomach ulcers caused by Helicobacter pylori bacteria

Early studies in humans show no effect of garlic on gastric or duodenal ulcers.

Uses based on tradition or theory

The below uses are based on tradition or scientific theories. They often have not been thoroughly tested in humans, and safety and effectiveness have not always been proven. Some of these conditions are potentially serious, and should be evaluated by a qualified healthcare provider.

Abortion, age-related memory problems, AIDS, allergies, amoeba infections, anti-bacterial, antioxidant, antitoxin, anti-viral, aphrodisiac, atrophic gastritis, arthritis, ascaridiasis (worms in the gut or liver), asthma, athlete's foot, benign breast disease, bile secretion problems, bladder cancer, bloody urine, breast fibromatosis, bronchitis, cholera, claudication (leg pain due to poor blood flow), colds, cough, Cryptococcal meningitis, cytomegalovirus infection, dental pain, digestive aid, diphtheria, diuretic (water pill), dysentery, dysmenorrhea, earache, fatigue, fever, gallstones, hair growth, headache, heart rhythm disorders, hemorrhoids, hepatopulmonary syndrome, HIV, hormonal effects, immune system stimulation, improved digestion, induction of vomiting, inflammation, inflammatory bowel disease, influenza, kidney problems, kidney damage from antibiotics, leukemia, liver cancer, liver health, malaria, mucous thinning, muscle spasms, nephrotic syndrome, obesity, parasites and worms, perspiration, pneumonia, premenstrual syndrome, prostate cancer, psoriasis, Raynaud's disease, ringworm (Tinea corpori,Tinea cruris), sedative, sinus decongestant, snake venom protection, spermicide, stomach ache, stomach acid reduction, stomach lining protection, stress (anxiety), stroke, thrush, toothache, traveler's diarrhea, tuberculosis, vaginal trichomoniasis, typhus, urinary tract infections, vaginal irritation, warts, well-being, whooping cough.

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