Carcinogenesis Advance Access originally published online on January 20, 2005
Carcinogenesis 2005 26(5):976-980; doi:10.1093/carcin/bgi028
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Carcinogenesis vol.26 no.5 © Oxford University Press 2005; all rights reserved.
Tea and circulating estrogen levels in postmenopausal Chinese women in Singapore
1 Department of Preventive Medicine, 2 Department of Obstetrics and Gynecology and 3 Department of Urology, University of Southern California Keck School of Medicine, Los Angeles, CA 90089, USA and 4 Department of Community, Occupational and Family Medicine, Faculty of Medicine, National University of Singapore, Singapore 117597
* To whom correspondence and reprints should be addressed at: USC/Norris Comprehensive Cancer Center, 1441 Eastlake Avenue, Los Angeles, CA 90089-9175, USA. Tel: +323 865 0480; Fax: +323 865 0139; E-mail: annawu{at}usc.edu
The role of tea in the etiology of breast cancer is controversial. We recently provided the first set of human evidence that breast cancer risk is significantly inversely associated with tea intake, largely confined to intake of green tea. Since black tea and green tea possess comparable levels of the total tea polyphenols that possess antioxidative activities, reasons for the paradoxical effects of green tea and black tea on breast cancer protection are not apparent. Some limited evidence suggests that green tea may have downregulatory effects on circulating sex-steroid hormones, whereas black tea may have upregulatory effects. We therefore, investigated the relationship between tea intake, and plasma estrogen and androstenedione levels in a cross-sectional study of healthy postmenopausal Chinese women in Singapore. In this group of 130 women, 84 were non or irregular (less than once a week) tea drinkers, 27 were regular (weekly/daily) green tea drinkers and 19 were regular (weekly/daily) black tea drinkers. Relative to plasma estrone levels in non- or irregular tea drinkers (29.5 pg/ml) the levels were 13% lower in regular green tea drinkers (25.8 pg/ml) and 19% higher in regular black tea drinkers (35.0 pg/ml). These differences in estrone levels were statistically significant (P = 0.03) inspite of adjusting for age, body mass index, intake of soy, and other covariates. A similar pattern of differences between tea intake, and plasma levels of estradiol (P = 0.08) and androstenedione (P = 0.14) were found. In addition, the tea–estrogen associations were observed irrespective of the genotype of catechol-O-methyltransferase (COMT), a major enzyme that aids in the excretion of tea polyphenols in humans. Larger studies are needed to confirm results from this cross-sectional study and to better understand the potentially differing effect of black and green tea on circulating estrogen levels and ultimately on the risk of breast cancer.
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