Hypertension, or high blood pressure, is the most important controllable risk factor for stroke. Garlic may help to keep blood vessels healthy, but it should not be used as a substitute for regular medical care. Have your blood pressure checked regularly by a health care professional, because hypertension can cause death or disability with no warning signs.
Mixed Results
Scientists' efforts to find out if garlic can lower your blood pressure initially had mixed results. In a 1994 review of eight studies on the effects of garlic, published in the "Journal of Hypertension," three trials demonstrated reduced systolic blood pressure and four studies showed that garlic reduced diastolic blood pressure compared with placebo. In a review published in the March 2001 "Archives of Internal Medicine," only three of 23 placebo-controlled studies showed significant reductions in diastolic blood pressure, and only one study found a reduction in systolic blood pressure in subjects taking garlic.
Severe Hypertension
Using garlic may have no effect if your blood pressure is normal, while those with elevated systolic blood pressure can expect benefits. Researchers from Hartford Hospital in Connecticut analyzed trials in which subjects started with an average systolic blood pressure of over 140 mm Hg and compared them to those involving subjects with more normal blood pressures. Garlic lowered systolic blood pressure an average of more than 16 mm Hg and diastolic blood pressure an average of more than 9 mm Hg in patients with more severe hypertension. Garlic did not lower measurements in patients who did not have elevated systolic blood pressure. The review was published in the December 2008 issue of "The Annals of Pharmcotherapy." Garlic has not been approved by the Food and Drug Administration to prevent or treat any condition.
Active Ingredients
Garlic has a high concentration of sulfur-containing compounds. When raw garlic is chopped, crushed or chewed, a sulfur-containing amino acid is acted on by the enzyme alliinase. Cooked garlic is less potent because alliinase is deactivated by heat. Commercial garlic preparations may have an unpredictable release of active ingredients. Because stomach acid also inhibits alliinase, dried garlic pills are more effective if they are enteric coated.
Adverse Effects
While some commercial preparations of garlic are purported to be tasteless and odorless, adverse effects of most forms of the plant include malodorous breath and body odor. Use fresh garlic with caution, as it could have undesirable social consequences. Ellen Tattelman, M.D., in her article on the health effects of garlic, published in the July 2005 "American Family Physician," lists additional unproven effects that have been attributed to garlic, including bloating, abdominal pain, allergic reactions and prolonged bleeding time. Tattelman suggests that high doses of garlic may have blood-thinning effects and should be discontinued if you are planning to have surgery. Inform your physician before using any natural health remedies.
