Ethnicity, body size, and estrogen levels in postmenopausal Hispanic and non-Hispanic white women.

Hispanic women are at lower risk for incident breast cancer, but the reasons for this lower risk are unknown. Among postmenopausal women, breast cancer risk is inversely associated with circulating levels of 2-hydroxyestrone but directly associated with levels of 16alpha-hydroxyestrone, according to most studies. Likewise, according to most research, the ratio of 2-hydroxyestrone/16alpha-hydroxyestrone is, therefore, inversely associated with breast cancer risk. We measured levels of these two circulating estrones as well as estradiol in 40 Hispanic women and 40 non-Hispanic white women who were all postmenopausal and not taking hormones. Compared with non-Hispanic white women, Hispanic women had 69% higher circulating levels of 2-hydroxyestrone (p = 0.04), and 10% lower levels of 16alpha-hydroxyestrone (p = 0.09). Consequentially, Hispanic women had more favorable estrogen profiles than non-Hispanic white women, with an 89% higher 2:16 ratio (p = 0.01). This finding was not substantially affected by adjustment for other breast cancer risk factors, including matching on body mass index (BMI). This ethnic difference in estrogen profile requires further research to establish whether there is a causal relationship to breast cancer risk that may, at least partially, explain why postmenopausal Hispanic women have a lower incidence of breast cancer.