Phytochemicals present in green tea change the metabolism of estrogen and can reduce the risk of breast cancer especially in post-menopausal women, according to a study from NIH's National Cancer Institute.
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 cancers.
AdvertisementSince 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 women.
'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 -
• Daily intake of green tea was more prevalent in postmenopausal than in pre- menopausal women.
• Intake of green tea was significantly associated with older age and Asian birthplace.
• Among pre-menopausal women, consumption of green tea was associated with significantly lower urinary concentrations of total estrogens and estrogen metabolites.
• In 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 factors.
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)'.
Reference: 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: 10.1186/1475-2891-12-25.