134 Handbook of herbs and spices
in delaying lipid oxidation compared with the level of 100 mg/kg but inferior to
dietary supplementation by 200 mg/kg a-tocopheryl acetate per kg. This study provided
indirect evidence that anti-oxidant compounds occurring in oregano essential oil
were absorbed by the rabbits and increased the antioxidant capacity of tissues.
8.4.3 Human studies
It is important that properly conducted trials be undertaken with human volunteers
for the herbs and spices to be shown to have an effective role in diet. In a study of
20 males who had enhanced platelet aggregation following dietary supplements of
100 g of butter, 5 g of dried ginger twice daily significantly inhibited platelet aggregation
induced by ADP and epinephrine (Verma et al., 1993). Not all studies were as conclusive.
A randomised double blind study in eight healthy males tested the effects of daily
doses of 2 g of dried ginger on platelet function. There were no differences in
bleeding time or platelet aggregation between the ginger and placebo groups (Lumb,
1994). In a similar study of 60 patients with coronary disease a daily dose of 4 g of
powdered ginger for three months did not affect ADP and epinephrine induced platelet
aggregation (Bordia et al., 1997). These studies indicate that relatively large doses of
ginger may be necessary to inhibit platelet function in humans.
In a small-scale study of the effects of garlic on LDL oxidation, a double blind
placebo controlled crossover study involving eight subjects, four men and four women,
mean age 68, four subjects took 1.2 g AGE three times a day for two weeks then two
weeks of no garlic (washout period) followed by two weeks of placebo. The remaining
four subjects took a placebo for the first two weeks followed by a two weeks washout
and two weeks of 1.2 g AGE three times a day (Lau, 2001). Blood was drawn at the
beginning of the experiment and at two, four, and six weeks and when the experiment
was completed. Plasma LDL was isolated and the CuSO 4 test repeated. The use of
garlic supplements was found to significantly increase the resistance of LDL to
oxidation.
8.5 Complex mixtures versus single compounds................................
Epidemiological studies established that the Mediterranean diet which is rich in
vegetables and herbs confirmed that the diet had health benefits for cardiovascular
sufferers and could therefore delay the onset of the disease (Knoops et al., 2004). In
order to identify the active components, the use of models and experimental animals
have both shown a positive response to the use of specific supplements in stages of
the disease such as oxidation of LDL. However randomised intervention trials that
have been conducted to prove the anti-oxidant hypothesis for supplements in humans
have not been convincing (Stanner et al., 2004). There is now evidence that there is
no support for the use of anti-oxidant supplements such as alpha-tocopherol, carotene
or ascorbic acid (Vivekanathan et al., 2003). One explanation for this is that in the
complex mixtures that exist in plants there are large numbers of anti-oxidant molecules
such as the polyphenols, whose role in the plant is to reduce oxidative stress by
donating hydrogen to other compounds, are more effective than compounds such as
ascorbic acid, b-carotene and a-tocopherol used in the supplements. The plant may
employ many of these compounds in the multistage process of removing oxygen
from the reactive oxygen species. Equally these compounds are available to animals