The relationship between bilateral oophorectomy and plasma hormone levels in postmenopausal women

Oophorectomy prior to natural menopause reduces breast cancer risk. We evaluated whether timing of oophorectomy (during premenopause vs. postmenopause) or hysterectomy was associated with hormone levels, specifically estradiol, estrone, estrone sulfate, testosterone, sex hormone binding globulin (SHBG), dehydroepiandrosterone sulfate (DHEAS), and prolactin, using data from the Nurses' Health Study. We included 2,251 postmenopausal women not using hormones who provided blood samples in 1989-1990 and/or 2000-2002, and who were controls in various nested case-control studies. We used multivariate linear mixed-effects models to assess geometric mean hormone levels by surgery status. Bilateral oophorectomy was associated with 25% lower testosterone levels versus women with natural menopause (20.8 vs. 15.5 ng/dL) (P < 0.0001) with no effect of timing of surgery (P = 0.80). SHBG levels were lower among women with a premenopausal oophorectomy (52.2 nmol/L) versus those with natural menopause (58.1 nmol/L) or a postmenopausal oophorectomy (62.0 nmol/L) (P = 0.02). There was no significant association of oophorectomy with estradiol, estrone, estrone sulfate, DHEAS, or prolactin levels (P ≥ 0.23). A simple hysterectomy was associated with a significant 8% lower testosterone (P = 0.03) and 14 % lower DHEAS (P = 0.02) levels compared with women with natural menopause but not with other hormone levels. Although limited by small numbers, our findings suggest no differential influence of timing of surgery on sex hormone levels. The reduction of testosterone levels in women with oophorectomy or hysterectomy suggests a possible role of this hormone in postmenopausal breast cancer development.