You may have heard the expression knowledge is power.
Well, today we’re going to give you more power
to control your diet and lifestyle by giving you the facts.
Welcome to the Nutrition Facts Podcast.
I’m your host, Dr. Michael Greger.
Today we look at the surprising power of green tea.
One of the healthiest beverages we can drink.
It has been associated with about a 30 percent reduction in breast cancer risk,
and may protect against gynecological malignancies,
such as ovarian cancer and endometrial cancer
as well as lower our cholesterol, blood sugar, and body fat.
In our first story we look at how green tea appears to work
by boosting the immune system.
The belief of green tea as a "wonder weapon" against
diseases dates back thousands of years.
I've talked about it in relation to chronic disease,
but what about infectious disease?
Interest in the antimicrobial activity of tea
dates back to a military medical journal in 1906,
suggesting that servicemen fill their canteens with tea
to kill off the bugs that caused typhoid fever.
However, this effect of tea was not studied further until
the late 1980s when tea compounds were pitted against
viruses and bacteria in test tubes and petri dishes.
But, what we care about is do they work in people?
I had dismissed this entire field of inquiry as clinically
irrelevant until genital warts.
External genital warts, caused by human wart viruses,
are one of the most common and fastest
spreading venereal diseases worldwide.
Patients with external genital warts present with one
or several cauliflower-like growths on the genitals and/or
anal regions, considerably impairing people's emotional
and sexual well-being. But rub some green tea ointment on and
you can achieve complete clearance of all warts in more
than 50% of cases.
Wow! If it works so well for wart viruses,
what about flu viruses?
Works great in a petri dish.
But what about in people?
Tea-drinking school children do seem to be protected,
but you don't know until it's put to the test.
If you give healthcare workers green tea compounds,
they come down with the flu about three times less often
than those given placebo.
In fact, just gargling with green tea may help.
While a similar effect was not found in high school students,
gargling with green tea may drop the risk of
influenza infection 7 or 8 fold
compared to gargling with water
in elderly nursing home residents
where flu can get really serious.
Unlike antiviral drugs, green tea appears to help by
boosting the immune system, enhancing the proliferation
and activity of gamma delta T cells, a type of immune cell
that acts as a first line defense against infection.
Subjects who drank six cups of tea per day had up to a
15-fold increase in infection-fighting interferon
production in as little as one week. But why?
There's actually a molecular pattern shared by cancer cells
and pathogens and with edible plant products, such as tea,
apples, mushrooms, and wine.
And so, eating healthy foods may help maintain our immune
cells on ready alert, effectively priming our gamma
delta T cells that can then provide natural resistance to
microbial infections and perhaps tumors.
I guess I shouldn't have been so surprised;
tea, after all, is a vegetable infusion.
You're basically drinking a hot water extraction
of a dark green leafy vegetable.
Within 40 minutes of green tea consumption,
we get a boost in antioxidant power in our bloodstream,
and within 60 minutes, an upregulation of DNA repair.
Tea consumption is associated with a reduced risk of
heart disease, stroke, and premature death in general,
with each additional cup of green tea a day
associated with a 4% lower mortality risk.
So maybe, drinking several cups of tea daily
can keep the doctor away as well as the mortician.
But what about cancer?
There is growing evidence from laboratory, population, and human interventional studies
that tea can exert beneficial disease-preventive effects,
and further may actually slow cancer progression.
Let’s review some of that evidence.
Not only do those who drink a lot of tea
appear to live years longer than those who drink less,
drinking lots of tea may delay the onset of cancer.
The women who did get cancer appeared to get it 7 years later
if they had been drinking lots of tea compared to those who consumed less,
whereas men had a 3 year delay,
the difference male vs female potentially due to smoking habits.
Green tea may be able to interfere with each of the stages of cancer formation,
the initiation of the first cancer cell, promotion into a tumor,
and the subsequent progression and spread.
Cancer is often initiated when a free radical
oxidizes our DNA causing a mutation,
but within 40 minutes of drinking green tea
you can get a nice spike in antioxidant power of your bloodstream.
This increase, in turn, may lower oxidative damage
to DNA and so decrease the risk of cancer.
Furthermore, in terms of genoprotective effects—
protecting our genes— pre-existing oxidation- induced
DNA damage was lower after drinking green tea
suggesting that it can boost DNA repair as well,
but we didn’t know for sure...
until now.
There’s a DNA repair enzyme in our body called OGG1
and within one hour of drinking a single cup of green tea
we can boost its activity
though after a week of tea drinking we can boost it even higher
so regular intake of green tea may have additional benefits
in the prevention and/or repair of DNA damage.
Tea is so DNA protective it can be used for sperm storage,
for fresh samples until it can be properly refrigerated;
and so anti-inflammatory, it can be used for pain control
as a mouthwash after wisdom tooth surgery.
And in terms of controlling cancer growth,
at a dose of green tea compounds that would make it
into someone’s organs after drinking 6 cups of tea
it can cause cancer cells to commit suicide, apoptosis,
programmed cell death while leaving normal cells alone.
There’s lots of chemo agents that can kill cancer through brute force,
but that can make normal cells vulnerable too.
So green tea appears to be potentially an ideal agent for cancer prevention:
little or no adverse side-effects, efficacious for multiple cancers
at achievable dose levels; can be taken orally.
We have a sense of how it works, by stopping cancer cells from growing
causing them to off themselves.
It’s cheap and has a history of safe acceptable use.
But this was all based on in-vitro studies in a test tube.
It needs to be evaluated in human trials—
give people with cancer green tea to see if it helps.
Finally today we examine the results of studies that use green tea
to try to stop or reverse the progression of oral cancer,
lung cancer, cervical cancer, and colon cancer cells.
Tea consumption may reduce the risk of getting oral cancer.
Not only may the consumption of tea boost the antioxidant power
of our bloodstream, within minutes of consumption,
and decrease the amount of free radical DNA damage
throughout our systems over time,
but it can also increase the antioxidant power of our saliva
and decrease the DNA damage within the inner cheek cells of smokers,
though not as much as stopping smoking all together.
So might this help precancerous oral lesions
from turning into cancerous oral lesions?
More than a 100,000 people develop oral cancer annually worldwide,
with a 5-year overall survival rate of less than the flip of a coin.
Oral cancer frequently arises from precancerous lesions in the mouth,
which each have a few percent chance every year from turning cancerous,
so what a perfect opportunity to see if green tea can help.
Fifty-nine patients with precancerous oral lesions
were randomized into a tea group,
in which capsules of powdered tea extract were given
as well as having the lesions painted with the green tea powder,
versus a control group that essentially got sugar pills
and were painted with nothing.
Within 6 months, lesions in 11 of the 29 in the tea group shrunk,
compared to only 3 out of 30 in the placebo group.
The results indicate that tea treatment can improve
the clinical manifestations of the oral lesions.
The most important question though is,
"Did it prevent them from turning cancerous?".
Because the trial only lasted a few months they couldn’t tell,
but when they scraped some cells off of the lesions
there was a significant drop in DNA damaged cells
within 3 months in the treatment group,
suggesting that things were going in the right direction.
Ideally, though we'd do a longer study
to see if they ended up with less cancer, and while we're at it,
how about a study where they just used swallowed tea components,
since most people don’t fingerpaint with tea in their mouths.
We didn’t have such a study, though until...
we did.
Same extraordinary clinical results with some precancerous lesions shrinking away,
and the study lasted long enough to see
if fewer people actually got cancer,
but there was just as much new cancer
in the green tea group as the placebo group.
So a higher response rate— I mean, the lesions looked better,
but no improvement in cancer-free survival,
which is the whole point.
These studies were done mostly on smokers and former smokers.
What about lung cancer?
Population studies suggest tea may be protective,
but let’s put it to the test.
Seventeen patients with advanced lung cancer
given up to the equivalent of like 30 cups of green tea a day,
but no objective responses were seen.
Another study of 49 cancer patients— 21 with lung cancer—
got between 4 and 25 cups worth of green tea compounds a day
and again no benefits were found.
The only benefit green tea may be able to offer lung cancer patients
is to help lessen the burns from the radiation treatments
when applied on the skin as green tea compresses
may be able to shorten the duration of the burns.
The protective effects of green tea applied topically
was also seen in precancerous cervical lesions,
where the twice a day direct application of a green tea ointment
showed a beneficial response in nearly three-quarters of the patients
compared to only about a 10% response in the untreated control group,
which is consistent with the anti-cancer effects of green tea compounds
on cervical cancer cells in a petri dish,
but when women just got green tea extract pills to take,
the pills didn’t seem to help.
I’ve talked about the potential benefit of green tea wraps for skin cancer—
is there any other cancer where green tea actually comes in direct contact?
Yes. Colon cancer, which grows from the inner surface of the colon
that comes in contact with food and drink.
In the colon, tea compounds are fermented by our good gut bacteria
into compounds like 3,4DHPA,
which appears to wipe out colon cancer cells
while leaving normal colon cells relatively intact in vitro.
So 136 patients with a history of polyps were randomized
to get green tea extract pills or not.
Now this was a study in Japan, so everyone was already drinking green tea.
So effectively this was comparing those who drank 3 cups a day to 4 cups a day,
but a year later on colonoscopy the added green tea group
had only half the polyp recurrence,
and the polyps that did grow were 25% smaller.
That’s pretty exciting!
Why hasn’t a larger follow-up study been done since?
Perhaps due to the difficulty in raising funds for the study,
because green tea is a cheap beverage, not a pharmaceutical.
But the good news is that thanks to a major cancer charity in Germany,
researchers are currently recruiting for the largest green tea cancer trial to date
in which more than 2000 patients will be randomized.
That's pretty exciting!
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please go to the Nutrition Facts Podcast landing page.
There you’ll find all the detailed information you need –
plus links to all of the sources we cite for each of these topics.
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