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Tea
and Diabetes
A
few
studies
have
hinted
that
teas—with
their
bounty
of
antioxidants
called
polyphenols—might
also
exhibit
antidiabetic
properties.
In
the
latest
such
trial,
Lucy
S.
Hwang
of
National
Taiwan
University
in
Taipei
measured
green
tea's
effect
on
insulin
action
in
rats
with
experimentally
induced
diabetes.
Hwang's
team
substituted
room-temperature
tea
for
drinking
water
for
half
of
the
animals.
After
12
weeks,
tea-drinking
rodents
exhibited
improved
insulin
sensitivity
and
lower
blood-glucose
concentrations
during
the
2
hours
after
each
meal,
the
researchers
reported
in
the
Feb.
1
Journal
of
Agricultural
and
Food
Chemistry.
In
related
test-tube
studies,
the
group
measured
how
well
fat
cells
from
these
animals
absorb
glucose,
an
action
that
in
the
body
would
lower
blood
sugar
concentrations.
The
cells
from
diabetic
rats
drinking
green
tea
absorbed
more
than
twice
as
much
of
the
sugar
as
did
cells
from
similar
animals
drinking
plain
water—indicating,
the
researchers
say,
that
the
tea
had
indeed
improved
the
fat
cells'
insulin
sensitivity.
Hwang's
group
has
now
tested
other
types
of
tea.
All
true
teas
are
made
from
leaves
from
the
same
species
of
plant.
Green
tea
is
unfermented,
whereas
black
and
other
teas
are
fermented
to
various
extents.
Like
the
green
tea
in
the
original
test,
semifermented
pou-chong
tea
"significantly
increased
glucose
uptake"
by
fat
cells
taken
from
diabetic
animals
that
drank
it,
Hwang
told
Science
News.
However,
fully
fermented
black
tea—the
favorite
of
most
Western
tea
drinkers—didn't
affect
glucose
absorption.
Since
different
teas
contain
different
polyphenols
that
might
underlie
the
fat-cell
response,
Hwang's
team
tested
the
antidiabetic
effects
of
several
polyphenols
from
the
best-performing
teas.
The
most
effective
turned
out
to
be
epigallocatechin
gallate,
an
agent
known
to
have
anticancer
properties
(SN:
7/23/94,
p.
61).
In
her
lab
tests,
the
compound
has
"insulinlike
activity,"
Hwang
says.
Hwang's
team
has
traced
the
green
tea's
antidiabetic
attributes
to
other
mechanisms
as
well.
In
rats,
green
tea
increased
the
number
of
insulin
receptors
on
cells
and
the
blood
concentration
of a
protein—GLUT-IV—that
helps
move
glucose
out
of
the
blood
and
into
cells.
Moreover,
Hwang
notes,
the
tea
activated
insulin-receptor
kinase,
an
enzyme
that
makes
the
receptors
available
to
bind
insulin
and
initiate
activity.
Coffee
and
Diabetese A new study of coffee and diabetes (Jan 2004) has shown that men who drank 6 cups of coffee a day reduced their chances of developing type-2 diabetes by half, and women who drank the same amount cut their risk by 30 percent. 126,000 people filled out questionnaires over the past 12-18 years with information about their coffee intake and other health questions.
According to their study, people who drank 7 cups a day (or more) were 50% less likely to develop type 2 diabetes. Drinking less coffee had less of an impact on diabetes onset. Researchers are still looking at the connection between coffee and diabetes, and caution people that 7 cups of coffee per day is enough to create other health problems.
In earlier studies, Dutch researchers discovered that there are compounds in coffee that aid the body's metabolism of sugar. Their study involved 17,000 men and women in the Netherlands. The results were published in November 2002, in the journal Lancet.
Tea and Insulin
Tea also has an effect on diabetes. Drinking tea can improve insulin activity up to 15 times, and it can be black, green or oolong. Herbal teas don't have any effect. The active compounds don't last long in the body, so you would have to drink a cup or more of tea every few hours to maintain the benefit. The catch is that you should drink it without milk (even soy milk), because milk seems to interact with the necessary chemicals and render them unavailable to your body.
Black & Green Tea
Both black tea and green tea are good for diabetes, a rat study shows. They also prevent diabetic animals from developing cataracts.
The findings appear in the May 4 issue of the Journal of Agricultural and Food Chemistry.
"Black and green tea represent a potentially inexpensive, nontoxic, and, in fact, pleasurable [blood-sugar-lowering] agent," the researchers write. "Tea may be a simple, inexpensive means of preventing or retarding human diabetes and the ensuing complications."
In the study, the researchers gave green and black teas to diabetic rats for three months.
Cataracts
They found both kinds of tea inhibited diabetic cataracts. The teas also had a blood-sugar-lowering effect.
To get the same dose of tea given to the rats, a 143-pound person would have to drink 4.5 8-ounce cups of tea every day.
Heart
Green tea may hold the key to keeping hearts clog-free.
Powerful antioxidants make up a third of the weight of dried tea leaves. The main one of these good-for-you compounds is called EGCG (or, if you're good at tongue twisters, epigallocatechin-3-gallate).
New mouse studies show that EGCG can slow the build-up of artery-clogging plaque. Yes, you've heard something like this before. Animal studies often show that antioxidants keep arteries from clogging. Human trials, however, are often disappointing.
That may soon change. What's different about this study is that it indicates the timing of green-tea-extract treatment makes a world of difference. Cardiologist Kuang-Yuh Chyu, MD, PhD, of Cedars-Sinai Medical Center, Los Angeles, and colleagues report the findings in the May 25 issue of Circulation.
"Most animal experiments evaluating the effects of antioxidants are started when the animals are young. Randomized clinical trials typically enroll adult patients with varying stages of plaques," Chyu says in a news release. "This discrepancy supports speculation that antioxidant treatment affects early but not later stages of plaque development."
Chyu's team studied mice fed a high-cholesterol diet and then given a plaque-inducing injury to their main heart artery. After the plaque-induced injury, some of the animals started getting injections of the green tea extract EGCG.
It worked. On day 21, the animals had 55% less plaque than those animals not given green tea extracts. By day 42, they had 73% less plaque. But the treatment had no effect when given to animals with fully mature plaque.
"It appears that antioxidant therapy would have therapeutic benefits only if initiated during a critical window very early in the formation of plaque," Chyu says.
Prediman K. Shah, MD, the study's senior researcher and director of the Cedars-Sinai cardiology division, says the findings move scientists closer to finding ways of preventing human heart disease.
"We look forward to developing and fine-tuning innovative prevention and treatment techniques in the future," Shah says in a news release.
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