Reversal of relation between body mass and endogenous estrogen concentrations with menopausal status.

Abstract

For more than a decade, results frompublished studies have indicated that therisk of breast cancer may be loweramong heavy premenopausal womenthan among their less obese counterparts(1-8). In heavy postmenopausal women,however, this risk is either increased orunchanged in comparison with non-obese postmenopausal women (9,10).The mechanism explaining this reversalin risk is unknown, although theoreticalexplanations have been proposed. Obesepostmenopausal women may have ele-vated risk from higher levels of circulat-ing estrogens secondary to increasedconversion of androgen to estrogen inadipose tissue (11) and a higher propor-tion of bioavailable estrogen due to thelow levels of sex hormone-bindingglobulin (SHBG) (12,13). Obese pre-menopausal women may exhibit agreater degree of anovulation, resultingin lower levels of both progesterone andestradiol, lower breast cell divisionrates, and, consequently, a lower risk ofbreast cancer (13-15).We had the opportunity to evaluatethe relation of body mass and hormonalprofiles in a group of 195 communityand 103 hospital control subjects from astudy of endometrial cancer describedelsewhere (16,17). Results of both con-trol groups were similar; therefore, thetwo groups were combined. Body massindex (BMI) (kg/m