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VICUS.COM (30 May 2000) -- In certain Western European countries,
people tend to consume a large amount of garlic, and these societies
tend to have a lower incidence of coronary
heart disease. Interestingly, these populations also eat large
amounts of onions, which tend to confound the data.
Is it the garlic or the onions that reduce heart disease? This is a
common problem when trying to determine causal relationships. It's one
thing to identify an association, but quite another to take the
critical step of establishing a cause-and-effect relationship.
For example, legend has it that there is an association between
Punxsutawney Phil seeing his shadow and six more weeks of wintry
weather. But does anybody really believe there is a cause-and-effect
relationship? (Hint: Statistically, Phil's prognostications have been
correct only 39% of the time.)
Garlic's modest effect on cholesterol
The good news is that researchers have established a modest
cause-and-effect relationship for the ability of garlic to lower blood
cholesterol concentrations.
A meta-analysis of
the controlled trials of garlic to reduce hypercholesterolemia shows
a significant reduction in total cholesterol levels. Garlic, in an
amount approximating one-half to one clove per day (600-900 mg), has
been shown to decrease total serum cholesterol levels by about 9% (Warshafsky, et
al., 1993). Other researchers have estimated the reduction at up
to 12%.
People with a total blood cholesterol concentration of greater than
200 mg/dL may expect to achieve a reduction of about 23 mg/dL.
Mechanism of action
In the laboratory, garlic and wild garlic reduce serum cholesterol
levels primarily by inhibiting cholesterol synthesis. Both have
similar effects, which are related to the amount of garlic used and to
a mixture of multiple compounds from the sulfur-containing class of
thiosulfinates, ajoenes and dithiins.
Chloroform and acetone/chloroform extracts of garlic and wild
garlic inhibit cholesterol synthesis 44% to 52%, while the five
individual sulfur-containing compounds in garlic-- ajoene,
methylajoene, allicin, 2-vinyl-4H-1,3-dithiin and
diallydisulfide -- inhibit cholesterol synthesis by 37% to 72%.
Commercial garlic products
Whether these findings extend to commercially prepared garlic
tablets or garlic oils remains to be proven. For example, total
cholesterol; LDL cholesterol, HDL cholesterol and triglycerides were
virtually unchanged in one study of a steam-distilled garlic oil
preparation (5 mg twice daily) vs. placebo for
12 weeks.
Other parameters such as cholesterol absorption, cholesterol
synthesis, mevalonic acid excretion and changes in the ratio of
lathosterol to cholesterol in serum were also not different as a
result of garlic vs. placebo treatment (Berthold et al.,
1998).
Conclusion
It is unclear whether the failure of one commercially prepared
garlic preparation is indicative of all preparations or if the problem
lies in an insufficient dosage.
For now, increasing dietary garlic provides one natural way to
reduce cholesterol. For those worried about the aftertaste (and
breath), consider that this socially unacceptable side effect of
garlic can be minimized by slicing the garlic instead of smashing it
in a press.
Healthful eating!
John
Russo Jr., PharmD, is senior vice president of medical
communications at Vicus.com. He is a pharmacist and medical writer
with more than 20 years of experience in medical education.
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