J Natl Cancer Inst. 1981 Oct; 67(4): 761-7.

Diet and reproductive hormones: a study of vegetarian and nonvegetarian postmenopausal women.

Armstrong BK, Brown JB, Clarke HT, Crooke DK, Hähnel R, Masarei JR, Ratajczak T.

In comparison with matched nonvegetarian women, postmenopausal vegetarian women were found to have lower urinary levels of estriol and total estrogens, lower plasma prolactin levels, and higher plasma sex hormone-binding globulin (SHBG) levels. These differences were not explained by differences in body weight or obesity. Plasma SHBG levels were highly correlated with plasma high-density lipoprotein cholesterol levels, which were also higher in vegetarians than in nonvegetarians. These hormonal differences may explain the lower rates of endometrial and possibly breast cancer that have been observed previously in vegetarian women.