Ethnic differences in post-menopausal plasma oestrogen levels: high oestrone levels in Japanese-American women despite low weight

Abstract

Until recently women in Japan were at very low risk of breast cancer (Ursin et al, 1994), particularly in the post-menopausal period when age-specific breast cancer rates remained essentially constant in contrast to the rates in the USA which continue to steadily increase in the post-menopausal period . Studies of plasma oestrogen concentrations in 'traditional' Asians (living in Asia) compared with Whites have found lower concentrations in the Asians (Goldin et al, 1986;Key et al, 1990;Shimizu et al, 1990). In particular, a study of post-menopausal Japanese women in Miyagi and non-Latina White women in Southern California found a 32% lower level of plasma oestrone (E1) and a 27% lower level of plasma oestradiol (E2) in the Japanese women (Shimizu et al, 1990).Breast cancer incidence rates in Japanese-American women now approach those of non-Latina White women (Ziegler et al, 1993). We therefore investigated whether post-menopausal plasma oestrogen and androstenedione (A; precursor of E1) levels in Japanese-American women were accordingly similar to those in (non-Latina) White women. The main comparison group was White women, as this group had been used as the comparison group in previous studies. We also included African-American women and Latina women to further our understanding of possible ethnic differences in estrogen metabolism. SUBJECTS AND METHODS SubjectsSubjects are part of a multi-ethnic cohort with an emphasis on studying diet and lifestyle characteristics in the aetiology of cancer. Details of this study are described elsewhere . The cohort included 215 251 subjects aged 40-75 years from Hawaii and Los Angeles county. These subjects had responded to a questionnaire mailed between 1993 and 1996. The response rates to the questionnaire were 25.5% in AfricanAmericans, 51.3% in Japanese-Americans, 21.3% in Latinas and 47.0% in Whites. The distributions of educational level and marital status of the cohort broadly resemble those reported by the US Census.Blood was collected from a random sample of healthy cohort members after receipt of informed consent. Participation in the blood collection phase has been over 70% in all ethnic groups. Eligible controls for this analysis included women who selfreported no history of cancer and in addition must either have experienced a natural menopause, or had both ovaries removed, or had a simple hysterectomy and be at least 55 years of age. Women who reported any hormone use in the 2 weeks before the blood draw were excluded. Sixty-six African-Americans, 30 JapaneseAmericans, 58 Latinas and 39 Whites were included in the study. Characteristics of these subjects are described in Table 1. Laboratory methodsPlasma aliquots from study subjects were stored in liquid nitrogen until analysis. Plasma levels of A, E1 and E2 were measured by radioimmunoassays previously validated in our laboratory Ethnic differences in post-menopausal plasma oestrogen levels: high oestrone levels in Japanese-American women despite low weight Summary Breast cancer incidence in Japanese-America...

Preferential induction of cytochrome P450 1A1 over cytochrome P450 1B1 in human breast epithelial cells following exposure to quercetin

“…More specifically, Asian women have a three-fold lower breast cancer risk than women in the United States, independent of body weight [33]. However, second and third generation descendants of women who migrated from Asia to Western countries have breast cancer risks similar to those of women in the host country, suggesting that lifestyle and dietary habits, and not genetic factors explain the low breast cancer risk of women in Asia [30,34,35]. Furthermore, epidemiologic studies have detected an association between phytoestrogen consumption, phytoestrogen levels in plasma and urine, and reduced risk of breast cancer [28,36].…”

Does place of birth influence endogenous hormone levels in Asian-American women?

“…In an effort to explain the international differences in breast cancer incidence rates, a number of investigators have compared hormone levels in healthy Asian and Caucasian women, with most focusing on differences in oestrogen levels (MacMahon et al, 1974;Moore et al, 1983;Trichopoulos et al, 1984;Goldin et al, 1986;Goodman et al, 1988;Bernstein et al, 1990;Shimizu et al, 1990;Key et al, 1990;Probst-Hensch et al, 2000) and a few examining androgens or androgen precursors (Bulbrook et al, 1967;Wang et al, 1976;Hayward et al, 1978). However, these studies could not distinguish the role of genetic differences from the effects of an Asian lifestyle on endogenous hormone levels.…”

“…These include findings from controls participating in a population-based case-control study of breast cancer in the US and China , and hormone comparisons between JapaneseAmericans and US Caucasians participating in the Multiethnic Cohort (Probst-Hensch et al, 2000). These studies showed oestrogens were higher in Caucasians than Asian women living in China, but similar to, if not slightly lower than levels in Japanese-Americans.…”

“…In the few studies that measured androgens (Bulbrook et al, 1967;Wang et al, 1976;Hayward et al, 1978), levels were higher in Caucasian women. The comparisons mainly concerned hormone levels in Asians living in the East with those of Caucasian women in the West (see Discussion) though a few studied Asian and Caucasian women living in the same region in the West (Goldin et al, 1986;Goodman et al, 1988;Probst-Hensch et al, 2000). In only two studies were women selected as representative of a defined population Probst-Hensch et al, 2000).…”

“…The comparisons mainly concerned hormone levels in Asians living in the East with those of Caucasian women in the West (see Discussion) though a few studied Asian and Caucasian women living in the same region in the West (Goldin et al, 1986;Goodman et al, 1988;Probst-Hensch et al, 2000). In only two studies were women selected as representative of a defined population Probst-Hensch et al, 2000). Different genetic susceptibilities alone are an unlikely explanation for international differences in breast cancer incidence, since rates among successive generations of Asian migrants to the West approach those of Caucasians (Buell, 1973).…”