Hello hhuang,
The ACRN (Australian Council for Responsible Nutrition) merged with
the Nutritional Foods Association of Australia in January 1999, to
form the Complementary Health Care Council of Australia, which has a
web site at: http://www.chc.org.au/ The 1997 ACRN report on the
Status of Antioxidant Nutrients is available for purchase from this
web site, at a cost of $5 (Australian). In order to purchase the
report, click on “Publications” in the left-hand navigation bar on the
home page. If you then select “list all publications”, this will be
the last item listed under “Reports”. Payment can be by cheque, money
order or credit card. No details are provided on whether any extra
cost is involved if ordering from outside Australia. If you wish to
contact the Council in advance of placing an order, contact details
are:
Complementary Health Care Council of Australia
PO Box 104
DEAKIN WEST ACT 2600
Australia
Phone: +61 (02) 6260 4022
Fax: +61 (02) 6260 4122
Email: chc@chc.org.au
With respect to journal articles, you will mostly find general
comments about the protective effects of fruit and vegetables, with
some reference to flavonoids. However, it is unlikely that any human
studies conducted so far will show effects relating to such a specific
dose as you mention. These studies are conducted by looking at the
dietary habits of groups of people, either comparing the usual diets
of cancer patients with those of healthy people matched for factors
such as age, sex, residence etc, or starting with a group of healthy
people and following them over many years to see what sort of diseases
occur and in whom. Both these types of studies are flawed to some
extent, because they rely on the honesty and/or memory of the
participants to report what they eat.
Furthermore, it has been pointed out by a number of nutrition
scientists that it is very difficult to obtain an accurate estimate of
total flavonoid intake when looking at dietary intake, because only
limited data is available on food contents. To get information about
the effects of a specific dose, it would be necessary to carry out a
study over many years with very strict record keeping of dietary
intake, and analysis of all the foods in order to determine flavonoid
levels, and possibly also supplementation of the diet with flavonoids.
Another complicating factor is that the word “cancer” is used to
describe a large spectrum of diseases. Substances that protect
against one type of cancer can increase the risk of another type.
I have summarised some studies which do show an association between
the intake of flavonoids and a decreased risk of cancer. These were
obtained from a Medline search at
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi The terms used in two
searches were: flavonoids, cancer, risk , and flavonoids, cancer,
protective
A review published in 1996 in the Journal of the American Dietetic
Association, October issue Vol 96, pp.1027-1039 “Vegetables, fruit,
and cancer prevention: a review” by K A Steinmetz and J D Potter,
summarizes results from 206 human epidemiologic studies and 22 animal
studies. The authors conclude that “The evidence for a protective
effect of greater vegetable and fruit consumption is consistent for
cancers of the stomach, esophagus, lung, oral cavity and pharynx,
endometrium, pancreas, and colon. The types of vegetables or fruit
that most often appear to be protective against cancer are raw
vegetables, followed by allium vegetables, carrots, green vegetables,
cruciferous vegetables, and tomatoes.” The substances which could
produce this protective effect include “dithiolthiones,
isothiocyanates, indole-3-carbinol, allium compounds, isoflavones,
protease inhibitors, saponins, phytosterols, inositol hexaphosphate,
vitamin C, D-limonene, lutein, folic acid, beta carotene, lycopene,
selenium, vitamin E, flavonoids, and dietary fiber”.
Abstract at http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=8841165&dopt=Abstract
A Finnish group showed that intake of flavonoids was associated with a
decreased incidence of cancer in a study of 9,959 Finnish men and
women aged 15-99 years, who were initially cancer free and who were
followed over the period 1967-1991. The decreased risk associated
specifically with flavonoid intake was mainly with respect to lung
cancer. “Of the major dietary flavonoid sources, the consumption of
apples showed an inverse association with lung cancer incidence, with
a relative risk of 0.42… after adjustment for the intake of other
fruits and vegetables.”
From: American Journal of Epidemiology, 1997, Volume 146, pages
223-230
Dietary flavonoids and the risk of lung cancer and other malignant
neoplasms.
by Knekt P, Jarvinen R, Seppanen R, Hellovaara M, Teppo L, Pukkala E,
Aromaa A.
Abstract at http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9247006&dopt=Abstract
A study in Uruguay looked at all patients with cancer of the oral
cavity, pharynx, larynx, and esophagus. They were matched with other
patients on the basis of age, sex, residence, and urban/rural status,
and the two groups were compared for any relationships between diet
and the risk of these cancers. Protein intake increased cancer risk.
“Non-nutritive substances, like flavonoids displayed a marked
reduction in risk of 70%”
From: Oral Oncology, 1999, Volume 35, pages 22-26
Diet and risk of cancer of the upper aerodigestive tract--II.
Nutrients.
by De Stefani E, Ronco A, Mendilaharsu M, Deneo-Pellegrini H.
Abstract at http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=10211306&dopt=Abstract
In a study of the effects of dietary phytoestrogens, including
flavonoids, on the risk of prostate cancer, 87 patients were compared
with 107 healthy controls. “Controls reported consuming higher amounts
of foods containing genistein, daidzein, and coumestrol and lower
amounts of foods containing campesterol and stigmasterol.” Cancer
risk was decreased with increasing intake of coumestrol and daidzein,
and genistein also had a slight protective effect. Daidzein and
genistein are both flavonoids.
Nutrition and Cancer, 1999, Vol 33 pages 20-25.
Phytoestrogen intake and prostate cancer: a case-control study using a
new database.
by Strom SS, Yamamura Y, Duphorne CM, Spitz MR, Babaian RJ, Pillow PC,
Hursting SD.
Abstract at http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=10227039&dopt=Abstract
A Spanish study found evidence of a protective effect against stomach
cancer of the flavonoid kaempferol, and a tendency for the flavonoid
quercetin to be protective. The study compared 354 patients with
cancer and 354 non-cancer patients, matched by age, gender, area of
residence and hospital. The risk of stomach cancer in the 25% of
patients with the highest intake of total flavonoids was only 44% of
that of the 25% of patients with the lowest intake.
Cancer Causes and Control, 1999, Volume 10, pages 71-75
Intake of specific carotenoids and flavonoids and the risk of gastric
cancer in Spain.
by Garcia-Closas R, Gonzalez CA, Agudo A, Riboli E.
Abstract at: http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=10334645&dopt=Abstract
A study in Hawaii of 582 patients with lung cancer and 582 controls
found that the risk of lung cancer decreased with intake of the main
food sources of the flavonoids quercetin (onions and apples) and
naringin (white grapefruit). The effect of onions was particularly
strong against squamous cell carcinoma.
Journal of the National Cancer Institute, 2000, Volume 92, pages
154-160
Intake of flavonoids and lung cancer.
by Le Marchand L, Murphy SP, Hankin JH, Wilkens LR, Kolonel LN.
Abstract at http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=10639518&dopt=Abstract
According to one group of authors who have reviewed the literature on
flavonoids from tea, “Human data are now emerging to support a
beneficial role for tea in cardiovascular disease, but the data with
respect to cancer risk at various sites remain inconclusive.” The
authors consider that more studies are required before any conclusions
can be reached.
Antioxid Redox Signal, 2001, Volume 3, pages 1009-10021
Tea flavonoids: bioavailability in vivo and effects on cell signaling
pathways in vitro.
by Wiseman S, Mulder T, Rietveld A.
Abstract at http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=11813977&dopt=Abstract
A Dutch study showed that the source of flavonoids may be important in
determining whether they have a protective effect against a specific
type of cancer. This study of 728 elederly men over 10 years showed
that catechins, one of the major groups of flavonoids, did not overall
show an association with decreased risk of epithelial or lung cancer.
However, a 7.5 mg increase in daily intake of catechins not derived
from tea (apples were the main source) did show a borderline effect in
reducing lung cancer risk, while the same increase had no effect if
the catechins were obtained from tea (it is not stated whether this
included both black and green tea).
International Journal of Cancer, 2001, Volume 92, pages 298-302
Dietary catechins and epithelial cancer incidence: the Zutphen elderly
study.
by Arts IC, Hollman PC, Bueno De Mesquita HB, Feskens EJ, Kromhout D.
Abstract at http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=11291060&dopt=Abstract
However, a study in 34,651 postmenopausal cancer-free women aged 55-69
years, who were followed for 2 years found that catechin intake was
associated with a decreased risk of rectal cancer, and there was a
non-signficant tendency for a decreased risk cancer of the upper
digestive tract, pancreas, and for blood cancers. Catechins derived
primarily from fruits, (+)-catechin and (-)-epicatechin, tended to be
associated with a decreased risk of upper digestive tract cancer,
while catechins derived from tea were associated with the decreased
risk of rectal cancer.
Cancer Causes and Control, 2002, Volume13, pages 373-382
Dietary catechins and cancer incidence among postmenopausal women: the
Iowa Women's Health Study (United States).
by Arts IC, Jacobs DR Jr, Gross M, Harnack LJ, Folsom AR.
Abstract at http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=12074507&dopt=Abstract
A review by L Le Marchand (Cancer preventive effects of flavonoids--a
review, published in Biomedical Pharmacotherapy, 2002, Volume 56,
pages 296-301) states that while it is possible to show in
epidemiological studies that plant-derived foods can protect against
cancer, “it has been difficult to identify specific components
responsible for this effect. Many phytochemicals have been shown to be
biologically active and they may interact to protect against cancer.”
Further information is being obtained from laboratory studies in
animals and in cell cultures. The author concludes “Although the
epidemiologic data on flavonoids and cancer are still limited and
conflicting, some protective associations have been suggested for
flavonoid-rich foods (soy and premenopausal breast cancer; green tea
and stomach cancer; onion and lung cancer).”
Abstract at http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=12224601&dopt=Abstract
Another review emphasises the complexity of the findings obtained so
far: “However, epidemiologic studies exploring the role of flavonoids
in human health have been inconclusive. Some studies support a
protective effect of flavonoid consumption in cardiovascular disease
and cancer, other studies demonstrate no effect, and a few studies
suggest potential harm. Because there are many biological activities
attributed to the flavonoids, some of which could be beneficial or
detrimental depending on specific circumstances, further studies in
both the laboratory and with populations are warranted.”
Annual Review of Nutrition, 2002, Volume 22, pages19-34
Dietary flavonoids: bioavailability, metabolic effects, and safety.
by Ross JA, Kasum CM.
Abstract at http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=12055336&dopt=Abstract
Since you mention green tea in the title of your question, I also did
a Medline search using the terms: green tea, cancer. Again, the
results of some studies show that green tea can decrease the risk of
some types of cancer, but there is insufficient data to be able to
reach any conclusions about the effects of a specific dose of
flavonoids from green tea.
A study in China showed that green tea decreased the risk of ovarian
cancer.
Cancer Epidemiology, Biomarkers and Prevention, 2002, Volume11, pages
713-718
Tea consumption and ovarian cancer risk: a case-control study in
China.
by Zhang M, Binns CW, Lee AH.
Abstract at http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=12163323&dopt=Abstract
Another Chinese study found that green tea reduced the risk of lung
cancer in female non-smokers, but not in smokers
Epidemiology, 2001, Volume 12, pages 695-700
A population-based case-control study of lung cancer and green tea
consumption among women living in Shanghai, China.
by Zhong L, Goldberg MS, Gao YT, Hanley JA, Parent ME, Jin F.
Abstract at http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=11679799&dopt=Abstract
A Japanese study found that green tea consumption was associated with
a decreased risk of breast cancer recurrence
Cancer Letters, 2001, Volume167, pages 175-182
Regular consumption of green tea and the risk of breast cancer
recurrence: follow-up study from the Hospital-based Epidemiologic
Research Program at Aichi Cancer Center (HERPACC), Japan.
by Inoue M, Tajima K, Mizutani M, Iwata H, Iwase T, Miura S, Hirose K,
Hamajima N, Tominaga S.
Abstract http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=11369139&dopt=Abstract
A study in China found a protective effect of green tea against
stomach cancer
International Journal of Cancer, 2001, Volume 92, pages 600-604
Protective effect of green tea on the risks of chronic gastritis and
stomach cancer.
by Setiawan VW, Zhang ZF, Yu GP, Lu QY, Li YL, Lu ML, Wang MR, Guo CH,
Yu SZ, Kurtz RC, Hsieh CC.
Abstract at http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=11304697&dopt=Abstract
JL Bushman reviewed studies on the effects on green tea in preventing
cancer in humans (Green tea and cancer in humans: a review of the
literature. Published in Nutrition and Cancer, 1998, Volume 31, pages
151-159, abstract at
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9795966&dopt=Abstract
)
The author looked at 31 studies and 4 reviews. Out of 5 studies of
the effect of green tea on colon cancer, three found a decreased risk
and one reported an increased risk. One out of 4 studies reported a
decreased risk of rectal cancer, two reported an increased risk, and
one found no effect. Two studies found a decreased risk of bladder
cancer. Six out of 10 studies showed a decreased risk of stomach
cancer, three found an increased risk and one found no effect,
however, the most detailed study found a decreased risk. Green tea had
a strong effect in decreasing the risk of esophageal cancer, and it
showed a slight effect in decreasing the risk of pancreatic cancer in
two out of three studies. Lung cancer risk was found to be decreased
by green tea consumption in one study, but may have been increased in
another study.
Another review of the effects of tea polyphenols concluded that
“Results from studies in rats, mice, and hamsters showed that tea
consumption protects against lung, forestomach, esophagus, duodenum,
pancreas, liver, breast, colon, and skin cancers induced by chemical
carcinogens… Because the epidemiologic studies and research findings
in laboratory animals have shown the chemopreventive potential of tea
polyphenols in cancer, the usefulness of tea polyphenols for humans
should be evaluated in clinical trials. One such phase 1 clinical
trial is currently under way at the MD Anderson Cancer Center in
collaboration with Memorial Sloan-Kettering Cancer Center. This study
will examine the safety and possible efficacy of consuming the
equivalent of >=10 cups (>=2.4 L) of green tea per day.”
From: Tea polyphenols: prevention of cancer and optimizing health
by Hasan Mukhtar and Nihal Ahmad
published in American Journal of Clinical Nutrition, Vol. 71, No. 6,
1698S-1702s, June 2000
You can read the full text of the article at
http://www.ajcn.org/cgi/content/full/71/6/1698S |
