Investigations of effects of garlic materials upon risk factors of atherosclerosis.
A brief review was provided of lipid metabolism, mechanisms of lipid lowering and coronary heart
disease risk factors (including the role of antioxidants). In addition, studies of lipid-lowering and other
anti-atherosclerotic effects of garlic materials were also reviewed.
Evaluation and development of techniques required to perform studies of the anti-atherosclerotic effects
of garlic were implemented, including evaluation of methods for measuring total antioxidant capacity and
the development of methods for the rapid isolation of low density lipoprotein (LDL).
The main objective of this project was to investigate the effects of garlic upon plasma lipids in rats and
healthy human subjects and the effects upon antioxidant status in healthy human subjects.
In a long-term study with old male rats, a low dose of garlic oil (c. O.5mg/Kg body weight/day) for 12.5
weeks provided in a high fat diet produced no significant reduction in plasma lipids or glucose. Upward
trends in plasma lipids early in the treatment period were similar to those reported from several previous
studies in which eventual reductions in plasma lipids were observed suggesting the possibility of a small
effect of garlic oil upon lipid metabolism.
Two randomised, double-blind, placebo-controlled human studies were carried out to investigate the
effects of capsules containing garlic oil dissolved in vegetable oil upon coronary heart disease risk factors
in normal subjects.
In the first study, 8.2 mg/day of garlic oil (or placebo) capsules were given to 51 subjects over an I 1-
week period. 95% confidence intervals were calculated for differences between garlic oil and placebo
groups of changes in plasma lipids, glucose and total antioxidant capacity between baseline and end-oftreatment.
No significant effects were observed, but it was found that plasma lipids and glucose trends
were more favourable with garlic oil treatment. Effects of garlic oil over placebo for cholesterol-related
variables and glucose were in opposite directions for males and females and this interaction between
genders reached significance for high density lipoprotein cholesterol, total cholesterol/high density
lipoprotein cholesterol ratio, calculated low density lipoprotein cholesterol and glucose of plasma. The
strong gender effect of garlic oil evidenced for plasma lipids and glucose implies potent effects of garlic
oil and suggests future garlic studies should include gender analyses.
In the second human study, 12 mg/day garlic oil (or placebo) capsules were given to 27 trained young
male athletes for 16 weeks. 95% confidence intervals were calculated for differences between garlic oil
and placebo groups of changes in plasma lipids, total antioxidant capacity and LDL composition between
baseline and end-of-treatment. It was found that the reduction in plasma triglycerides (p=O.09) of the
garlic oil group in comparison with the placebo group was accompanied by increases in density, a
significant reduction in triglycerides / protein and a trend towards reduction of cholesterol/protein of the
LDL fraction. A trend towards reduced total antioxidant capacity / protein of LDL appear to reflect garlic
oil effects upon lipid composition of LDL rather than directly upon antioxidants. Non-significant trends
towards small improvements in maximal oxygen intake test-duration and less plasma glucose depletion
with garlic oil were observed.
Overall, the results from the human studies provide some encouragement to the view that garlic oil could
reduce coronary heart disease risk in normal persons and that this possibility deserves further