Why garlic reduces blood pressure, by researchers

GARLIC may be useful in addition to
medication to treat high blood pressure, a
study suggests.
Australian doctors enrolled 50 patients in a
trial to see if garlic supplements could help
those whose blood pressure was high,
despite medication. They report in scientific
journal Maturitas that those given four
capsules of garlic extract a day had lower
blood pressure than those on placebo.
The British Heart Foundation said more
research was needed.
Garlic has long been thought to be good for
the heart. Garlic supplements have
previously been shown to lower cholesterol
and reduce high blood pressure in those
with untreated hypertension.

How hibiscus tea lowers blood pressure, ‘bad’ cholesterol

New research findings indicate that the
flower and leaf extracts of hibiscus could
provide the next novel drug for
hypertension and coronary heart diseases.
NIGERIAN researchers have confirmed that
drinking tea made with flower extracts of
Hibiscus rosa-sinensis (popularly called
Hibiscus flower) lowered blood pressure in
hypertensive patients.
Researchers have also demonstrated how
the flower extracts of hibiscus could be
used to reduce weight, prevent obesity and
coronary heart diseases like atheroslerosis
by lowering the blood levels of low density
lipo-protein (LDL) ‘bad’ cholesterol.
Atherosclerosis, which involves deposits of
fatty substances, cellular waste products,
calcium and fibrin (is a fibrous protein
involved in the clotting of blood); and is the
leading cause of illness and death in most
countries.
However, a local study has found that
although hibiscus leaf extract reduced
blood pressure, the integrity of the kidney
may be compromised if it is used in high
doses for the treatment of hypertension.
Botanically called Hibiscus rosa-sinensis,
hibiscus belongs to the plant family
Malvaceae. Hibiscus has many species and is
a primary ingredient in many herbal teas.
Hibiscus rosa-sinensis is closely related to
Hibiscus sabdariffa (also called roselle or
zobo in Nigeria).
According to The useful plants of west
tropical Africa, Volume 4 by H. M. Burkill, the
flower is used as “abortifacients (a
substance that induces abortion), ecbolics
(hastening labour or abortion); genital
stimulants/depressants; laxatives (foods,
compounds, or drugs taken to induce bowel
movements or to loosen the stool), etc.;
menstrual cycle; paralysis, epilepsy,
convulsions, spasm; sedatives, etc.”
A recent study by Nigerian researchers at
the University of Benin has demonstrated
the effects of aqueous extracts of the
leaves of Hibiscus rosa-sinensis on renal
function in hypertensive rats.
The study was published in African Journal
of Biochemistry Research. The researchers
include: Imafidon E. Kate of the Department
of Biochemistry, Faculty of Life Sciences;
and Okunrobo O. Lucky of the Department
of Pharmaceutical Chemistry, Faculty of
Pharmacy, University of Benin, Edo State.
The researchers wrote: “Most people with
high blood pressure are over weight,
weight loss lowers blood pressure
significantly in those who are both over
weight and hypertensive. In fact, reducing
body weight by as little as ten pounds can
lead to a significant reduction in blood
pressure; weight loss appears to have a
stronger blood pressure-lowering effect
than dietary salt restriction. Salt loading had
earlier been shown to cause hypertension
in rats.
“Reduction in weight gain of hypertensive
rats observed is in agreement with the
report of some workers. The administration
of H. rosa-sinensis leaf extract showed
blood lowering effect in both normotensive
(normal blood pressure) and hypertensive
rats. Blood pressure is the product of
cardiac output and peripheral resistance of
the blood vessels.
“ The administration of H. rosa-sinensis
probably decreased the blood pressure by
decreasing the heart rate, which is a major
determinant of the cardiac output.
Significant increase in the sodium level of
normotensive rats administered with the
crude extract in spite of significant
reduction in the blood pressure of these
rats compared with the control shows that
H. rosa-sinensis may interfere with the
normal function of the kidney and hence
produces increased salt retention.
“This observation is further strengthened
by the increased urea concentration,
although the change in total protein
concentration was insignificant in those
normotensive rats administered with the
crude extract. In addition, AST, and ALT
concentrations were increased in these rats
compared with control.”
Aspartate aminotransferase (AST) and
Alanine aminotransferase (ALT) are enzymes
found primarily in the liver, as well as the
kidneys, cardiac and skeletal muscle.
The researchers concluded: “ These results
show that the leaves of this plant may have
a deleterious effect on the kidney.
Hypertensive rats administered with the
extract had significant increase in urea, AST
and sodium ion (Na+) concentration
compared with normal control. This result
therefore, shows that although, the
administration of H. rosa-sinensis reduced
blood pressure in albino rats, the use of the
plant may have an unpleasant effect on the
kidney. ”
Nigerian scientists have also studied the
tissue lipid profile of rats administered
aqueous extract of Hibiscus rosa-sinensis.
The study was published in the Journal of
Basic and Applied Sciences. The lead
researcher Kate E. Imafidon of the
Biochemistry Department, Faculty of life
Sciences, University of Benin determined
the effect of orally administered aqueous
extract of the leaves of Hibiscus rosa-
sinensis on tissue lipid profile of albino rats.
Lipid profiles are risk indicators of coronary
heart disease. Strong correlations have been
shown between increased plasma total
cholesterol, low density lipoprotein (LDL)
‘ bad’ cholesterol and increased incidence of
coronary heart disease such as
atheroslerosis.
According to the study, oral administration
of crude extract of H. rosa-sinensis to albino
rats at doses 200, 500 and 700mg/Kg body
weight resulted in a significant increase in
body weight of animals in the highest dose
group.
The study reads: “The dose dependent
increase in liver triacylglycerol (the main
constituent of vegetable oil and animal fats),
total cholesterol and LDL cholesterol suggest
impairment in lipid transport. This is as a
result of the fact that there was no
concomitant increase in kidney or heart
lipid levels. Triacylglycerols are transported
in the blood stream by very low density
lipoprotein (VLDL).
“Alternative use of carbohydrates as a
result of the engorgement of liver tissues
with fats may have produced increase in
weight in the highest dose group. HDL
cholesterol levels were not increased at any
of the dose levels, HDL cholesterol has a
protective effect against cardiovascular
disease as it removes excess cholesterol
from circulation and carries it back to the
liver where it is degraded or converted into
bile acids. The lipid raising effect of some
trado-medicinal plants have been reported.
Some workers had earlier observed
increase in serum cholesterol on
administration of crude drug extract; and
observed an increase in serum cholesterol
levels on administration of aqueous extract
of Aplotaxis lappa
“ This work has therefore demonstrated the
ability of H. rosa-sinensis to influence liver
metabolism towards increased synthesis of
lipids. This effect is however dose-
dependent suggesting that the use of H.
rosa-sinensis in alternative or
complementary medicine should not exceed
the 500 mg/kg dose level.”
A 2008 United States of America Department
of Agriculture (USDA) study shows
consuming hibiscus tea lowers blood
pressure in a group of pre-hypertensive
and mildly hypertensive adults. Three cups
of tea daily resulted in an average drop of
8.1 point in their systolic blood pressure,
compared to a 1.3 point drop in the
volunteers who drank the placebo
beverage. Study participants with higher
blood pressure readings (129 or above) had
a greater response to hibiscus tea: their
systolic blood pressure went down by 13.2
points. These data support the idea that
drinking hibiscus tea in an amount readily
incorporated into the diet may play a role in
controlling blood pressure, although more
research is required.
Generally, drinking tea has been found to
lower low-density lipoprotein, the LDL “bad”
cholesterol, in a small group of volunteers in
an ARS study reported in the Journal of
Nutrition.
The study showed no effect on high-
density lipoprotein, the HDL “good”
cholesterol. The study’s authors concluded
that drinking black tea, in combination with
following a prudent diet moderately low in
fat, cholesterol and saturated fatty acids,
reduces total and LDL cholesterol by
significant amounts and may reduce the
risk of coronary heart disease.
Other studies have evaluated some
ethnomedicinal value of Hibiscus rosa-
sinensis. H. rosa sinensis has been used for
the treatment of a variety of diseases as
well as to promote wound healing.
Researchers have determined the wound-
healing activity of the ethanol extract of H.
rosa- sinensis flower in rats, using excision,
incision, and dead space wound models.
Local traditional practioners in Western
Nigeria has reported that cold aqueous
extract of H. rosa-sinensis leaves could be
used as an aphrodisiac.
Researchers have also studied the blood
sugar-lowering (hypoglycemic) activity of
an ethanol extract of H. rosa-sinensis in rats.
Anti-implantation activity of water extract
of leaves of H. rosa-sinensis has also been
investigated. It has also been investigated
that H. rosa-sinensis extract exerts a
protective effect against the tumour
promotion stage of cancer development.
Traditionally this plant is used for the
control of dysfunctional uterine bleeding
and as an oral contraceptive. Some of the
chemical constituents isolated from this
plant are cyanidin, quercetin,
hentriacontane, calcium oxalate, thiamine,
riboflavin, niacin and ascorbic acid.
Flavonoids are also present.