The incidence of breast cancer is
3 to 4 times higher in the U.S. compared to Japan. Again, green tea, commonly
consumed in Japan, is an important source of dietary phytochemicals that fight
Since there are limited studies
of green tea intake and risk of breast cancer and most studies of green tea
have not considered pre- and postmenopausal women separately, Barbara Fuhrman at
Division of Cancer Epidemiology and Genetics, National Cancer Institute,
National Institutes of Health, USA and her colleagues set out to examine the
associations of green tea intake and caffeine intake with urinary estrogens and
estrogen metabolites among cancer-free pre-menopausal and postmenopausal
Japanese American women.
Estrogen (estradiol, estriol, and
estrone) are hormones produced by the ovaries to regulate fertility and help in
development of the female reproductive system. The estrogen levels reduce
during menopause and may cause hot flashes and mood swings but high levels of
estrogen may increase the risk of breast cancer, especially in post menopausal
'Because green tea catechins have
been observed to reduce catalytic activity of certain cytochrome p450 (CYP)
enzymes, we hypothesized that green tea may influence breast cancer risk, in
part, by modifying the production or metabolism of estrogens, known carcinogens
of the breast. Caffeine, present in teas and other foods, is also known to
modify expression and/or activity of some metabolic enzymes, but has not been
found to have a consistent effect on breast cancer risk', said the researchers.
The study, published in the
Nutrition Journal, included 191 Japanese-American women without breast cancer
(119 pre-menopausal women and 72 postmenopausal women) who were asked to
provide 12-hour overnight urine samples. During in-person interviews, the
participants were queried about frequency of intake of green tea, black tea,
coffee, decaffeinated coffee and caffeinated soda.
Results showed that -
of green tea was more prevalent in postmenopausal than in pre- menopausal women.
green tea was significantly associated with older age and Asian birthplace.
women, consumption of green tea was
associated with significantly lower
urinary concentrations of total estrogens and estrogen metabolites
postmenopausal women, urinary estrone
and estradiol were approximately 20 percent lower and 40 percent lower,
respectively, in women drinking green tea daily compared to those drinking less
than once a week
, irrespective of their BMI, Asian origin, age at menarche
and consumption of soy.
• Green tea intake was inversely associated
with 16-hydroxylated estrogen metabolites
, which are prone to behave like
'super-estrogen' and can result in mutations, abnormal growth and increased
risk of breast cancer.
Interestingly, a study published
in the February issue of Cancer Research pointed out that urinary 17-epiestriol,
rather than 16-hydroxylated estrogen metabolites, were associated with
increased risk of breast cancer. Urinary 17-epiestriol, too, showed a
significant, inverse trend with green tea intake in the present study.
The researchers also found that
the geometric mean urinary concentrations of total estrogens and estrogen
metabolites of the postmenopausal Japanese-American group was about half of the
levels that were found in Caucasian postmenopausal women from New York.
However, this difference was not noted in pre-menopausal women, whether
Japanese American or Caucasian American. The researchers are not sure if these
differences are due to ethnicity, diet, cultural practices, or technical
What they are sure of is the
finding that green tea may reduce postmenopausal breast cancer risk. In their
words - 'Our finding that green tea intake is associated with reduced urinary
estrone and estradiol in our sample of postmenopausal Japanese-American women,
does support the hypothesis that green tea intake may reduce postmenopausal
breast cancer risk by modifying exposures to endogenous estrogens (estrogens
produced by the body)'.
Fuhrman BJ, Pfeiffer RM, Wu AH, Xu X, Keefer LK,
Veenstra TD, Ziegler RG. Green tea intake is associated with urinary estrogen
profiles in Japanese-American women. Nutr J. 2013 Feb 15;12(1):25. doi: