Green tea and the risk of breast cancer: pooled analysis of two prospective studies in Japan

Abstract

In a pooled analysis of two prospective studies with 35 004 Japanese women, green-tea intake was not associated with a lower risk of breast cancer (222 cases), the multivariate relative risk for women drinking X5 cups compared with o1 cup per day being 0.84 (95% confidence interval 0.57 -1.24, Trend P ¼ 0.69). Although laboratory studies have suggested a protective effect of green tea on breast cancer risk, few epidemiological studies have examined the association. A case -control study of Asian Americans in the United States found a lower risk of breast cancer in association with green-tea intake (Wu et al, 2003), whereas a prospective cohort study in Japan found no association (Key et al, 1999). To further examine the association between green-tea consumption and the risk of breast cancer, we conducted a pooled analysis of two population-based prospective cohort studies among women in rural northern Japan. MATERIALS AND METHODSDetails of the design of the two cohort studies are described elsewhere (Tsubono et al, 2001;Nakaya et al, 2003). Briefly, Cohort 1 started in 1984 and included 17 353 women aged X40 years (94% response rate) (Tsubono et al, 2001); Cohort 2 started in 1990 and included 24 769 women aged 40 -64 years (93% response rate) (Nakaya et al, 2003). Self-administered questionnaires covered recent (Cohort 1) or usual (Cohort 2) consumption of green tea and used the same five frequency categories ranging from 'never' to 'X5 cups per day'. It had a reasonably high level of validity and reproducibility (Ogawa et al, 2003). After exclusion of those with missing responses or with a prior history of cancer, 14 409 subjects in Cohort 1 and 20 595 in Cohort 2 remained. We followed up vital and residential status of the study subjects by population registries. Through population-based cancer registries, 103 incident cases of breast cancer were identified in Cohort 1 (9 years follow-up with 111 267 person-years) and 119 in Cohort 2 (7 years follow-up with 151 882 person-years).We estimated relative risk (RR) and 95% confidence interval (CI) of breast cancer according to green-tea consumption, using Cox's proportional-hazards regression with the adjustment for age and potential confounders. To obtain a summary measure of results between Cohorts 1 and 2, the general variance-based method was used to pool each RR and 95% CI. We repeated all analysis after excluding breast cancer cases diagnosed in the first 3 years of follow-up (38 in Cohort 1 and 40 in Cohort 2). P-values for the test of linear trend were calculated by treating the green-tea consumption category as an ordinal variable. All reported P-values are two-tailed. Table 1 compares the characteristics of subjects in the highest and the lowest categories of green-tea consumption. Subjects in Cohort 1 with higher intake tended to be postmenopausal, while such women in Cohort 2 tended to be slightly older, postmenopausal and have a higher body mass index. Subjects in both cohorts with a lower intake tended to drink black tea less frequently and coffee mo...

Diet and breast cancer

“…For fruits and vegetables we included 6 cohorts, [31][32][33][34][35][36] 1 meta-analysis 37 and 1 pooled analysis 38 ; 11 cohorts for carbohydrates [11][12][13]18,21,22,[39][40][41][42][43] ; 11 cohorts for antioxidants 16,18,32,33,35,36,[44][45][46][47][48] ; and 11 cohorts for milk 10,13,14,24,25,27,31,[49][50][51][52] ; 2 cohorts for vitamin D 51,53 ; 5 cohorts for soy 18,31,[54][55][56] ; 5 cohorts 31,57-59 and 1 pooled analysis for green tea 58 ; 1 cohort for heterocyclic amines 60...…”

Tea and human health: biomedical functions of tea active components and current issues

“…A cohort study on 18 244 Chinese men followed up for up to 12 years maintains that tea catechins may prevent gastric and esophageal cancers (Sun et al, 2002). Another cohort study on 72 943 individuals implies a decreased risk for the development of gastric cancer in women, not in men, who drink more than five cups of tea per day (Suzuki et al, 2004). However, there were also some negative results (Galanis et al, 1998;Inoue et al, 1998;Huang et al, 1999;Zhou et al, 2008).…”

“…Leong et al (2008) used the C3(1)/SV40 mouse model to evaluate the chemopreventive effects of green tea on human breast cancer, which showed that the administration of 0.5% polyphenol in drinking water significantly suppressed the development of tumor growth by 40% compared to tap water-fed animals. The association between green tea intake and breast cancer risk has been investigated in five prospective cohort studies conducted in Japan (Nagano et al, 2001;Suzuki et al, 2004;Iwasaki et al, 2010), Singapore (Yuan et al, 2005;Inoue et al, 2008), and Shanghai, China (Dai et al, 2010). These prospective cohort studies with a total of 2067 breast cancer cases, show that there is no association between the breast cancer risk and green tea drinking.…”

Personality and cancer survival: the Miyagi cohort study

“…We have reported the design of this prospective cohort study in detail elsewhere (Fukao et al, 1995;Nakaya et al, 2003;Suzuki et al, 2004). Briefly, we delivered two self-administered questionnaires to all 51 921 residents aged 40 -64 years in 14 municipalities of Miyagi Prefecture in rural northern Japan from June through August 1990.…”