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.