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Science Groups Forum Index » Life Extension » Green Tea: Mixed Reviews For Cancer Prevention
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| vauxall |
 Posted: Tue Jul 21, 2009 3:33 pm |
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x-no-archive:yes
http://www.cochrane.org/reviews/en/ab005004.html
Abstract
Background
Tea is one of the most commonly consumed beverages worldwide. Teas
from the plant Camellia sinensis can be grouped into green, black and
oolong tea. Cross-culturally tea drinking habits vary. Camellia
sinensis contains the active ingredient polyphenol, which has a
subgroup known as catechins. Catechins are powerful antioxidants. It
has been suggested that green tea polyphenol may inhibit cell
proliferation and observational studies have suggested that green tea
may have cancer-preventative effects.
Objectives
To critically assess any associations between green tea consumption
and the risk of cancer incidence and mortality.
Search strategy
We searched eligible studies up to January 2009 in the Cochrane
Central Register of Controlled Trials (CENTRAL), MEDLINE, EMBASE,
Amed, CancerLit, Psych INFO and Phytobase and reference lists of
previous reviews and included studies.
Selection criteria
We included all prospective, controlled interventional studies and
observational studies, which either assessed the associations between
green tea consumption and risk of cancer incidence or that reported on
cancer mortality.
Data collection and analysis
At least two review authors independently applied the study criteria,
extracted data and assessed methodological quality of studies. Due to
the nature of included studies, which were mainly epidemiological,
results were summarised descriptively according to cancer diagnosis.
Main results
Fifty-one studies with more than 1.6 million participants were
included. Twenty-seven of them were case-control studies, 23 cohort
studies and one randomised controlled trial (RCT).
Twenty-seven studies tried to establish an association between green
tea consumption and cancer of the digestive tract, mainly of the upper
gastrointestinal tract, five with breast cancer, five with prostate
cancer, three with lung cancer, two with ovarian cancer, two with
urinary bladder cancer one with oral cancer, three further studies
included patients with various cancer diagnoses.
The methodological quality was measured with the Newcastle-Ottawa
scale (NOS). The 9 nested case-control studies within prospective
cohorts were of high methodological quality, 13 of medium, and 1 of
low. One retrospective case-control study was of high methodological
quality and 21 of medium and 5 of low.
Results from studies assessing associations between green tea and risk
of digestive tract cancer incidence were highly contradictory. There
was limited evidence that green tea could reduce the incidence of
liver cancer. The evidence for esophageal, gastric, colon, rectum, and
pancreatic cancer was conflicting. In prostate cancer, observational
studies with higher methodological quality and the only included RCT
suggested a decreased risk in men consuming higher quantities green
tea or green tea extracts. However, there was limited to moderate
evidence that the consumption of green tea reduced the risk of lung
cancer, especially in men, and urinary bladder cancer or that it could
even increase the risk of the latter. There was moderate to strong
evidence that green tea consumption does not decrease the risk of
dying from gastric cancer. There was limited moderate to strong
evidence for lung, pancreatic and colorectal cancer.
Authors' conclusions
There is insufficient and conflicting evidence to give any firm
recommendations regarding green tea consumption for cancer prevention.
The results of this review, including its trends of associations, need
to be interpreted with caution and their generalisability is
questionable, as the majority of included studies were carried out in
Asia (n = 47) where the tea drinking culture is pronounced. Desirable
green tea intake is 3 to 5 cups per day (up to 1200 ml/day), providing
a minimum of 250 mg/day catechins. If not exceeding the daily
recommended allowance, those who enjoy a cup of green tea should
continue its consumption. Drinking green tea appears to be safe at
moderate, regular and habitual use. |
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| cnorwood |
| Posted: Wed Jul 22, 2009 6:27 pm |
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The below dosage is probably why there is such a divergence between
studies. Way too many scientists have quoted this amount '250mg' for 3
to 5 cups. This is only true if the whole leaf is ingested like in
powdered sencha. This mimics an alcohol extraction. EGCG is hard to
extract by water, and the water extraction of 3 to 5 cups is unlikely
to get you to 5mg let alone 250mg. It is seriously odd that this
misconception has lasted this long. Do these scientists not read that
which they cite? It is a sad state of affairs.
Desirable
Quote: green tea intake is 3 to 5 cups per day (up to 1200 ml/day), providing
a minimum of 250 mg/day catechins. If not exceeding the daily
recommended allowance, those who enjoy a cup of green tea should
continue its consumption. Drinking green tea appears to be safe at
moderate, regular and habitual use. |
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| Paul Antonik Wakfer |
| Posted: Wed Jul 22, 2009 11:31 pm |
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On Jul 22, 2:27 pm, cnorwood <cnorw...@gmail.com> wrote:
Quote: The below dosage is probably why there is such a divergence between
studies. Way too many scientists have quoted this amount '250mg' for 3
to 5 cups. This is only true if the whole leaf is ingested like in
powdered sencha. This mimics an alcohol extraction. EGCG is hard to
extract by water, and the water extraction of 3 to 5 cups is unlikely
to get you to 5mg let alone 250mg. It is seriously odd that this
misconception has lasted this long. Do these scientists not read that
which they cite? It is a sad state of affairs.
Desirable
green tea intake is 3 to 5 cups per day (up to 1200 ml/day), providing
a minimum of 250 mg/day catechins. If not exceeding the daily
recommended allowance, those who enjoy a cup of green tea should
continue its consumption. Drinking green tea appears to be safe at
moderate, regular and habitual use.
It has been the practice of me and Kitty for several years now, to
save all remains from our daily tea brewing (a blend of black and
jasmine green teas, red and green rooibos, gogi berries, lemon grass,
yerba matte, hibiscus blossoms, fresh cut ginger) and include these in
our smoothie making, which we do every third day. My reasoning has
been that I was certain that there are some chemicals which would not
be well extracted by merely lengthy soaking in boiling water. The same
reasoning applies to both juicing fruits and vegetables, unless all
the remaining pulp is consumed in some other manner, and boiling
fruits or vegetables, unless all the water is consumed (which can be
done in various ways: as soup stock, mixed with juice drinks or just
drunk by itself - we often use the same boiling water for several
cookings before consuming it in one of these ways).
In fact, our daily compost disposal is very small because so much of
the fruit and vegetable remains goes into the blender as part of the
smoothie including: apple cores, all peels/skins (except avocado,
pineapple and banana), all seeds (except avocado, mango and peach/plum/
nectarine/cherry ) - we even include egg shells and the small leaves
that come with the strawberries (all extremal parts after thorough
washing, of course). Some research showed us that papaya seeds are
full of isothiocyanates and we found that when ground or finely
chopped they taste like a combination of onion and garlic and they
make an excellent spice for omelettes and salad dressings.
Although the webpage is not current (I actually do the smoothie making
every 2nd eating day - remember we fast 1 day out of 3), the
information and photos give the reader a good idea of how this
smoothie is prepared - http://morelife.org/personal/health/smoothie.html
--Paul Wakfer
MoreLife for the rational - http://morelife.org
Reality based tools for more life in quantity and quality
The Self-Sovereign Individual Project - http://selfsip.org
Self-sovereignty, rational pursuit of optimal lifetime happiness,
individual responsibility, social preferencing & social contracting |
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| cnorwood |
| Posted: Thu Jul 23, 2009 3:12 pm |
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You put even French chefs to shame, who are notorious for not wasting
anything. Good on ya. I will have to try out your papaya seed
discovery. Thanks for the link.
For others who may be worried about the caffeine content of the whole
leaf, it is approximately the same as what you normally get in a cup
of tea. Caffeine extracts very quickly in water. Sencha tea has more
of the goodies than other teas and can be found powdered. I get mine
from O-cha.
On Jul 22, 6:31 pm, Paul Antonik Wakfer <p...@morelife.org> wrote:
Quote: It has been the practice of me and Kitty for several years now, to
save all remains from our daily tea brewing (a blend of black and
jasmine green teas, red and green rooibos, gogi berries, lemon grass,
yerba matte, hibiscus blossoms, fresh cut ginger) and include these in
our smoothie making, which we do every third day. My reasoning has
been that I was certain that there are some chemicals which would not
be well extracted by merely lengthy soaking in boiling water. The same
reasoning applies to both juicing fruits and vegetables, unless all
the remaining pulp is consumed in some other manner, and boiling
fruits or vegetables, unless all the water is consumed (which can be
done in various ways: as soup stock, mixed with juice drinks or just
drunk by itself - we often use the same boiling water for several
cookings before consuming it in one of these ways).
In fact, our daily compost disposal is very small because so much of
the fruit and vegetable remains goes into the blender as part of the
smoothie including: apple cores, all peels/skins (except avocado,
pineapple and banana), all seeds (except avocado, mango and peach/plum/
nectarine/cherry ) - we even include egg shells and the small leaves
that come with the strawberries (all extremal parts after thorough
washing, of course). Some research showed us that papaya seeds are
full of isothiocyanates and we found that when ground or finely
chopped they taste like a combination of onion and garlic and they
make an excellent spice for omelettes and salad dressings.
Although the webpage is not current (I actually do the smoothie making
every 2nd eating day - remember we fast 1 day out of 3), the
information and photos give the reader a good idea of how this
smoothie is prepared -http://morelife.org/personal/health/smoothie.html
--Paul Wakfer
MoreLife for the rational -http://morelife.org
Reality based tools for more life in quantity and quality
The Self-Sovereign Individual Project -http://selfsip.org
Self-sovereignty, rational pursuit of optimal lifetime happiness,
individual responsibility, social preferencing & social contracting |
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| David |
| Posted: Fri Jul 24, 2009 11:32 am |
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Guest
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On Jul 22, 2:27 pm, cnorwood <cnorw...@gmail.com> wrote:
Quote: The below dosage is probably why there is such a divergence between
studies. Way too many scientists have quoted this amount '250mg' for 3
to 5 cups. This is only true if the whole leaf is ingested like in
powdered sencha. This mimics an alcohol extraction. EGCG is hard to
extract by water, and the water extraction of 3 to 5 cups is unlikely
to get you to 5mg let alone 250mg. It is seriously odd that this
misconception has lasted this long. Do these scientists not read that
which they cite? It is a sad state of affairs.
Desirable
green tea intake is 3 to 5 cups per day (up to 1200 ml/day), providing
a minimum of 250 mg/day catechins. If not exceeding the daily
recommended allowance, those who enjoy a cup of green tea should
continue its consumption. Drinking green tea appears to be safe at
moderate, regular and habitual use.
Aren't the researchers referring to 250 mg of *total* catechins as
opposed to 250 mg specifically of EGCG? |
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| cnorwood |
| Posted: Fri Jul 24, 2009 4:22 pm |
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Guest
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The 250mg number is total catechins per gram of dry weight sencha
green tea. Maccha and Gyokuro has 78mg/g , Hojicha has 24mg/g and
Bancha has 5mg/g.
About 30% of green tea is catechins and of of that 50-65% is EGCG. All
catechins are extracted at less than 1% in water compared to alcohol,
with the exclusion of EC. EC extracts 50% in water compared to alcohol
but only makes up 4% of all catechin content. So via water extraction,
if you extract from 1g tea, you will get approximately 1.2mg of
catechin content. This makes alcohol or whole leaf ingestion over 200
fold more effective than water extract.
The only way to get the values stated would be to look at the catechin
content of green tea, particularly sencha. If we do look at the
content of sencha, we find it matches perfectly with their values, and
many times they even reference the study showing alcohol extract.
To replicate extract studies by drinking green tea, you need to be
drinking powdered sencha. If you are ingesting whole green tea leaves
that are not sencha, it will take about three times the amount in
weight to get the same effects. Since, the difference between whole
leaf ingestion and water extraction is so huge, the main focus is just
to ingest the whole leaf but for study replication make it powdered
sencha.
Also note that freshness matters. The stuff they sell at starbucks or
in tea bags can be many times less effective. Order fresh large leaf.
Personally, I consume about 2g of fresh powdered sencha a day for
about 300mg EGCG and 500mg total catechins. Keep it in a light proof
container in your fridge after shipment in nitrogen packed pouch from
Japan (really not very expensive about $15 a month last I checked).
As you can see, these differences could make huge impacts on the
effectiveness of studies. Given that the researchers regularly
misquote and compare alcohol extracts to water extracts does not give
me confidence in their ability to conduct epidemiological population
studies.
References:
Journal of Chromatography A, 1011 (2003) 173–180
Mutation Research 496 (2001) 75–81
Email me if you want either paper.
Chris
On Jul 24, 6:32 am, David <david.spro...@gmail.com> wrote:
Quote: Aren't the researchers referring to 250 mg of *total* catechins as
opposed to 250 mg specifically of EGCG? |
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| cnorwood |
| Posted: Fri Jul 24, 2009 4:26 pm |
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Guest
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The 250mg number is total catechins per gram of dry weight sencha
green tea. Maccha and Gyokuro has 78mg/g , Hojicha has 24mg/g and
Bancha has 5mg/g.
About 30% of green tea is catechins and of of that 50-65% is EGCG.
All
catechins are extracted at less than 1% in water compared to alcohol,
with the exclusion of EC. EC extracts 50% in water compared to
alcohol
but only makes up 4% of all catechin content. So via water
extraction,
if you extract from 1g tea, you will get approximately 1.2mg of
catechin content. This makes alcohol or whole leaf ingestion over 200
fold more effective than water extract.
The only way to get the values stated would be to look at the
catechin
content of green tea, particularly sencha. If we do look at the
content of sencha, we find it matches perfectly with their values,
and
many times they even reference the study showing alcohol extract.
To replicate extract studies by drinking green tea, you need to be
drinking powdered sencha. If you are ingesting whole green tea leaves
that are not sencha, it will take about three times the amount in
weight to get the same effects. Since, the difference between whole
leaf ingestion and water extraction is so huge, the main focus is
just
to ingest the whole leaf but for study replication make it powdered
sencha.
Also note that freshness matters. The stuff they sell at starbucks or
in tea bags can be many times less effective. Order fresh large leaf.
Personally, I consume about 2g of fresh powdered sencha a day for
about 300mg EGCG and 500mg total catechins. Keep it in a light proof
container in your fridge after shipment in nitrogen packed pouch from
Japan (really not very expensive about $15 a month last I checked).
As you can see, these differences could make huge impacts on the
effectiveness of studies. Given that the researchers regularly
misquote and compare alcohol extracts to water extracts does not give
me confidence in their ability to conduct a review of epidemiological
studies.
References:
Journal of Chromatography A, 1011 (2003) 173–180
Mutation Research 496 (2001) 75–81
If you want either of these papers email me.
Chris
On Jul 24, 6:32 am, David <david.spro...@gmail.com> wrote:
Quote: Aren't the researchers referring to 250 mg of *total* catechins as
opposed to 250 mg specifically of EGCG? |
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| Back to top |
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| cnorwood |
| Posted: Fri Jul 24, 2009 4:28 pm |
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Guest
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To clarify a bit:
The 250mg number is total catechins per gram of dry weight sencha
green tea. Maccha and Gyokuro has 78mg/g , Hojicha has 24mg/g and
Bancha has 5mg/g.
About 30% of green tea is catechins and of of that 50-65% is EGCG.
All catechins are extracted at less than 1% in water compared to
alcohol,
with the exclusion of EC. EC extracts 50% in water compared to
alcohol but only makes up 4% of all catechin content. So via water
extraction, if you extract from 1g tea, you will get approximately
1.2mg of
catechin content. This makes alcohol or whole leaf ingestion over 200
fold more effective than water extract.
The only way to get the values stated would be to look at the
catechin content of green tea, particularly sencha. If we do look at
the
content of sencha, we find it matches perfectly with their values,
and many times they even reference the study showing alcohol extract.
To replicate extract studies by drinking green tea, you need to be
drinking powdered sencha. If you are ingesting whole green tea leaves
that are not sencha, it will take about three times the amount in
weight to get the same effects. Since, the difference between whole
leaf ingestion and water extraction is so huge, the main focus is
just to ingest the whole leaf but for study replication make it
powdered
sencha.
Also note that freshness matters. The stuff they sell at starbucks or
in tea bags can be many times less effective. Order fresh large leaf.
Personally, I consume about 2g of fresh powdered sencha a day for
about 300mg EGCG and 500mg total catechins. Keep it in a light proof
container in your fridge after shipment in nitrogen packed pouch from
Japan (really not very expensive about $15 a month last I checked).
As you can see, these differences could make huge impacts on the
effectiveness of studies. Given that the researchers regularly
misquote and compare alcohol extracts to water extracts does not give
me confidence in their ability to conduct a review of epidemiological
studies.
References:
Journal of Chromatography A, 1011 (2003) 173–180
Mutation Research 496 (2001) 75–81
If you want either of these papers email me.
Chris
On Jul 24, 6:32 am, David <david.spro...@gmail.com> wrote:
Quote: Aren't the researchers referring to 250 mg of *total* catechins as
opposed to 250 mg specifically of EGCG? |
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|
| Back to top |
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| cnorwood |
| Posted: Fri Jul 24, 2009 4:35 pm |
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Guest
|
To clarify a bit:
The 250mg number is total catechins per gram of dry weight sencha
green tea. Maccha and Gyokuro has 78mg/g , Hojicha has 24mg/g and
Bancha has 5mg/g.
About 30% of green tea is catechins and of of that 50-65% is EGCG. All
catechins are extracted at less than 1% in water compared to alcohol,
with the exclusion of EC. EC extracts 50% in water compared to alcohol
but only makes up 4% of all catechin content. So via water extraction,
if you extract from 1g tea, you will get approximately 1.2mg of
catechin content. This makes alcohol or whole leaf ingestion over 200
fold more effective than water extract.
The only way to get the values stated would be to look at the catechin
content of green tea, particularly sencha. If we do look at the
content of sencha, we find it matches perfectly with their values, and
many times they even reference the study showing alcohol extract. To
replicate extract studies by drinking green tea, you need to be
drinking powdered sencha. If you are ingesting whole green tea leaves
that are not sencha, it will take about three times the amount in
weight to get the same effects. Since, the difference between whole
leaf ingestion and water extraction is so huge, the main focus is just
to ingest the whole leaf but for study replication make it powdered
sencha.
Also note that freshness matters. The stuff they sell at starbucks or
in tea bags can be many times less effective. Order fresh large leaf.
Personally, I consume about 2g of fresh powdered sencha a day for
about 300mg EGCG and 500mg total catechins. Keep it in a light proof
container in your fridge after shipment in nitrogen packed pouch from
Japan (really not very expensive about $15 a month last I checked).
As you can see, these differences could make huge impacts on the
effectiveness of studies. Given that the researchers regularly
misquote and compare alcohol extracts to water extracts, it does not
give me confidence in their ability to conduct or review
epidemiological studies. When it comes to green tea, I look at a study
per study basis since the studies can be set up so badly.
References:
Journal of Chromatography A, 1011 (2003) 173–180
Mutation Research 496 (2001) 75–81
If you want either of these papers email me.
Chris
On Jul 24, 6:32 am, David <david.spro...@gmail.com> wrote:
Quote: Aren't the researchers referring to 250 mg of *total* catechins as
opposed to 250 mg specifically of EGCG? |
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| Back to top |
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