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

In 1983-87, we conducted a population-based case-control study of breast cancer in Asian women living in California and Hawaii, in which migration history (a composite of the subject's place of birth, usual residence in Asia (urban/rural), length of time living in the West, and grandparents' place of birth) was associated with a six-fold risk gradient that paralleled the historical differences in incidence rates between the US and Asian countries. This provided the opportunity to determine whether endogenous hormones vary with migration history in Asian-American women. Plasma obtained from 316 premenopausal and 177 naturally premenopausal study controls was measured for levels of estrone (E1), estradiol (E2), estrone sulphate (E1S), androstenedione (A), testosterone (T), dehydroepiandrosterone (DHEA), dehydroepiandrosterone sulphate (DHEAS), progesterone (PROG) and sex hormone-binding globulin (SHBG). Levels of the oestrogens and sex hormone-binding globulin did not differ significantly between Asian- and Western-born women, although among premenopausal women, those least westernised had the lowest levels of E1, E2, and E1S. Androgen levels, particularly DHEA, were lower in women born in the West. Among premenopausal women, age-adjusted geometric mean levels of DHEA were 16.5 and 13.8 nmol l(-1) in Asian- and Western-born women respectively; in postmenopausal women these values were 11.8 and 9.2 nmol l(-1), (P<0.001) respectively. Among postmenopausal women, androgens tended to be highest among the least westernised women and declined as the degree of westernisation increased. Our findings suggest that aspects of hormone metabolism play a role in population differences in breast cancer incidence.