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Open Access Research article

Comparison of postmenopausal endogenous sex hormones among Japanese, Japanese Brazilians, and non-Japanese Brazilians

Motoki Iwasaki1*, Yoshio Kasuga2, Shiro Yokoyama3, Hiroshi Onuma3, Hideki Nishimura4, Ritsu Kusama5, Gerson Shigeaki Hamada6, Ines Nobuko Nishimoto7, Maria do Socorro Maciel8, Juvenal Motola9, Fábio Martins Laginha9, Roberto Anzai10 and Shoichiro Tsugane1

Author affiliations

1 Epidemiology and Prevention Division, Research Center for Cancer Prevention and Screening, National Cancer Center, Tokyo, Japan

2 Department of Surgery, Nagano Matsushiro General Hospital, Nagano, Japan

3 Department of Breast and Thyroid Surgery, Nagano Red Cross Hospital, Nagano, Japan

4 Department of Surgery, Nagano Municipal Hospital, Nagano, Japan

5 Department of Surgery, Nagano Hokushin General Hospital, Nagano, Japan

6 Nikkei Disease Prevention Center, São Paulo, Brazil

7 Statistical Section/Head and Neck Surgery and Otorhinolaryngology Department, Hospital A.C. Camargo, São Paulo, Brazil

8 Breast Surgery Department, Hospital A.C. Camargo, São Paulo, Brazil

9 Department of Breast Surgery, Hospital Pérola Byington, São Paulo, Brazil

10 Department of Breast Surgery, Hospital Santa Cruz, São Paulo, Brazil

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Citation and License

BMC Medicine 2011, 9:16  doi:10.1186/1741-7015-9-16

Published: 16 February 2011

Abstract

Background

Differences in sex hormone levels among populations might contribute to the variation in breast cancer incidence across countries. Previous studies have shown higher breast cancer incidence and mortality among Japanese Brazilians than among Japanese. To clarify the difference in hormone levels among populations, we compared postmenopausal endogenous sex hormone levels among Japanese living in Japan, Japanese Brazilians living in the state of São Paulo, and non-Japanese Brazilians living in the state of São Paulo.

Methods

A cross-sectional study was conducted using a control group of case-control studies in Nagano, Japan, and São Paulo, Brazil. Participants were postmenopausal women older than 55 years of age who provided blood samples. We measured estradiol, estrone, androstenedione, dehydroepiandrosterone sulfate (DHEAS), testosterone and free testosterone by radioimmunoassay; bioavailable estradiol by the ammonium sulfate precipitation method; and sex hormone-binding globulin (SHBG) by immunoradiometric assay. A total of 363 women were included for the present analyses, comprising 185 Japanese, 44 Japanese Brazilians and 134 non-Japanese Brazilians.

Results

Japanese Brazilians had significantly higher levels of estradiol, bioavailable estradiol, estrone, testosterone and free testosterone levels, and lower SHBG levels, than Japanese. Japanese Brazilians also had significantly higher levels of bioavailable estradiol, estrone and DHEAS and lower levels of SHBG and androstenedione than non-Japanese Brazilians. Levels of estradiol, testosterone and free testosterone, however, did not differ between Japanese Brazilians and non-Japanese Brazilians. These differences were observed even after adjustment for known breast cancer risk factors. We also found an increase in estrogen and androgen levels with increasing body mass index, but no association for most of the other known risk factors.

Conclusions

We found higher levels of estrogens and androgens in Japanese Brazilians than in Japanese and levels similar to or higher than in non-Japanese Brazilians. Our findings may help explain the increase in the incidence and mortality rate of breast cancer among Japanese Brazilians.