Garlic - Scientific Background
Garlic helps keep arteries healthy.
In one observational study, people taking more than 300 milligrams per day of standardized garlic powder for 2 or more years showed less age-related damage to the wall of the aorta, the main trunk artery, than control participants (Breithaupt-Grogler et al 1997). The aortas of 70-year-old participants who took garlic were as elastic as the aortas of 55-year-old participants who did not take garlic. This finding may help explain results that garlic reduces blood pressure.
Garlic may improve cholesterol and blood fat levels.
In a 12-week, randomized, controlled trial (Adler and Holub 1997) in men with moderately high cholesterol levels, 900 milligrams of garlic per day reduced total cholesterol levels by 12%, significantly improved their ratio of high-density cholesterol (HDL, the good cholesterol) to total cholesterol levels, and reduced blood pressure.
A double-blind, cross-over study (Steiner et al 1996) found significant decreases in cholesterol levels and blood pressure in men with moderately elevated cholesterol levels who were taking 7.2 grams of aged garlic extract per day over 6 months.
In a large-scale, randomized, controlled trial in patients with elevated cholesterol or blood fats, taking 800 milligrams of standardized garlic powder (Kwai, Sapec) per day resulted, on average, in a 12% drop in cholesterol and a 17% drop in levels of certain blood fats known as triglycerides (Mader, 1990).
Phelps and Harris (1993) found that 600 milligrams per day of garlic powder protected low-density cholesterol (LDL, the bad cholesterol) against oxidation; oxidized LDL is damaging to the arterial walls.
In people with a tendency toward excessive blood clotting, taking 800 mg of powdered garlic in a form that passes the stomach intact (enteric-coated tablets) reduced unwanted clotting (Kiesewetter et al, 1993).
In a quantitative review of 28 clinical studies on the effect of garlic preparations, Warshafsky et al (1993) found evidence to suggest that garlic reduces total serum cholesterol. One-half to one clove of garlic per day or the equivalent supplement lowered cholesterol levels by a conservative average of 9%.
Reuter (1995) reviewed a similar set of studies and concluded that a daily dose of 600 to 900 milligrams of garlic powder would, on average, reduce serum cholesterol levels by about 10% and triglyceride levels by about 14%.
A quantitative summary study (meta-analysis) by Silagy and Neil (1994) of 16 previous studies found an average 12% reduction of serum cholesterol among participants who all took the same dried garlic powder preparation (Kwai). Although the study of Neil et al (1996) does not support this conclusion, the totality of evidence appears to favor a beneficial effect of garlic preparations on cholesterol levels.
Garlic may contribute to lower cancer risk.
After reviewing about 30 studies on garlic and cancer, Dausch and Nixon (1990) concluded that garlic and onion consumption is associated with reduced mortality from cancer, and that garlic may work through several pathways.
In test-tube research, Pinto et al (1997) found that substances from garlic were able to inhibit the growth of human prostate cancer cells, and Sakamoto et al (1997) found the same inhibition of growth in human lung cancer cells. It is not clear if these test-tube results apply to persons who eat garlic.
By exposing leukemia cells to the garlic compound ajoene, Dirsch et al (1998) were able to trigger programmed cell death. The same treatment did not adversely affect healthy blood cells.
Garlic enhances immune response in cells in the laboratory.
At low-to-moderate doses, one of the compounds formed when garlic is heated, diallyl trisulfide (DATS), appears to make certain cells of the immune system more active against cancer cells (Feng et al 1994).
Similar results were obtained by Morioka et al (1993), who conclude that extracts from aged garlic are powerful enhancers of immune response. This activation may also contribute to the ability of garlic to fight infections.
Garlic may improve resistance to infections.
Garlic appears to be effective against many kinds of microbes that cause infections (Hughes and Lawson 1991). Allicin, one of the main biologically active compounds of garlic, is an antibiotic. At least against one bacterial species, allicin is more potent than penicillin (Block 1985).
In the test tube, extracts of allicin can disable infection-causing amoebas by inhibiting key processes that many microbes need to cause infections (Ankri et al 1997).
Test-tube studies show garlic extracts to be protective of tissue against certain viruses (Guo et al 1993). Weber et al (1992) found that the garlic compounds ajoene and allicin were the most effective ingredients of garlic extracts against herpes simplex, common cold, and a number of other viruses.
Garlic may be useful in treating fungus infections.
Even in small quantities, the garlic compounds ajoene (Yoshida et al 1987), diallyl trisulfide (Shen et al 1996), a garlic extract containing allicin, and a number of other sulfuric garlic compounds (Davis et al 1994) inhibited fungi by interfering with fungus metabolism (San-Blas et al 1997).
With a cream containing 0.4% ajoene from garlic, Ledezma et al (1996) were able to cure 100% of patients with athlete's foot over the course of 2 weeks.
