NEW YORK (Reuters Health) - Eating a clove of garlic or taking a commercial garlic supplement every day to reduce cholesterol levels doesn't work, a new study shows. However, garlic may protect the heart in other ways, the study's authors suggest.

Dr. Christopher D. Gardner of Stanford University Medical School in California and colleagues found that adults with moderately high levels of LDL ("bad") cholesterol who ate the equivalent of one clove of garlic a day, six days a week, for six months showed no significant changes in their LDL levels or any other measurement of blood lipids or fats.

"Garlic supplements or dietary garlic in reasonable doses are unlikely to produce lipid benefits," Gardner and his team conclude in the Archives of Internal Medicine.

Crushing garlic triggers the release of allicin, a chemical that blocks the formation of cholesterol in a lab dish, and many animal studies have found garlic can lower cholesterol, the researchers write. However, human studies of garlic's cholesterol-lowering powers have had mixed results.

Given that the biological activity of garlic may vary based on its formulation, Gardner and his colleagues compared three different forms -- raw garlic, powdered garlic supplement, and aged garlic extract -- to placebo in 192 men and women with moderately elevated LDL cholesterol levels. The researchers took blood samples from the participants' monthly for six months, and found no significant reductions in LDL cholesterol for any of the four groups.

The current study used higher levels of allicin than investigated in past trials, Gardner and his team note, and also involved more participants than almost all previous investigations. However, they add, garlic could be helpful for people with higher levels of cholesterol than individuals in the current study.

Also, they suggest, garlic may have other cardiovascular benefits, perhaps to slow hardening of the arteries or reduce a propensity to form blood clots.

"The results do not demonstrate that garlic has no usefulness in the prevention of cardiovascular disease," Drs. Mary Charlson and Marcus McFerren of Weill Cornell Medical College in New York City write in an editorial accompanying the study. The supplements are probably, safe, they add, but "the jury is still out" on their heart-protective effects.