Complementary Alternative Cardiovascular Medicine

Chapter 3 / Botanical Medicine and CVD 33
ation of garlic products found that 23 out of 24 brands tested released only
15% of their stated allicin potential when subjected to the USP testing
method. To ensure greater bioavailability, some researchers argue that garlic
powder supplements should no longer be standardized to allicin potential
but on dissolution allicin release (29,30). Until test products can be assured
of containing and making bioavailable the key active constituents in garlic,
conducting and evaluating clinical trials will be extremely difficult.
The benefits of long-term garlic consumption might best be viewed as
a tonic effect on the cardiovascular system. Garlic has been shown to have
mild antihypertensive (31), antiarrhythmic (32), antithrombotic, and
antiatherogenic activites. The latter properties result from platelet aggregation
inhibition, cholesterol biosynthesis inhibition and enhancing
fibrinolysis (33,34). Garlic oil, aged garlic, fresh garlic, and garlic powder
inhibit platelet aggregation via interference with the cyclooxygenase
mediated thromboxane synthesis pathway (35). Raw garlic inhibited
cyclooxygenase activity noncompetitively and irreversibly (36). After 26
wk of garlic consumption, there was roughly an 80% reduction in serum
thromboxane in healthy male volunteers eating 3 g fresh garlic daily (36).
Cooked garlic has a lower inhibitory effect on platelet aggregation than
raw garlic (37).
The antiatherogenic activity of garlic has been demonstrated in a clinical
study conducted in Europe. A randomized, double-blind, placebocontrolled
trial was conducted with 152 men and women who were
diagnosed with advanced plaque accumulation and one other cardiac risk
factors (high cholesterol and hypertension). Patients were randomized to
take 900 mg garlic (Kwai ® ) or placebo for 48 mo. Ultrasound was used to
measure plaque in carotid and femoral arteries at 0, 16, 36, and 48 mo. At
48 mo: a 2.6% reduction in plaque volume was noted in the garlic group,
compared to a 15.6% increase in the placebo group (38).
In addition to widespread belief in the lipid-lowering effects of garlic,
many lay people also consider garlic a useful treatment for high blood
pressure (39). Research demonstrates that animals that were fed garlic,
along with a high-cholesterol diet, had reduced blood pressure and lower
elevations in cholesterol than control animals (40). However, many of the
animal studies that show the antihypertensive activity of garlic are difficult
to interpret, as the garlic was often administered intravenously.
In one pilot study in humans, the antihypertensive activity of garlic was
noted to occur within 5 h of administration of a single dose of 2400-mg
dried garlic, with the effect lasting roughly 14 h (41). A meta-analysis of
the efficacy of garlic and blood pressure found a mean difference in the
absolute change (from baseline to final measurement) of systolic blood
pressure that was greater in the subjects who were treated with garlic than