Breast cancer risk factors in two distinct ethnic groups: Indian and Pakistani vs. American premenopausal women

Asian Indians from the Indian subcontinent have low rates of breast cancer, but studies on breast cancer risk factors in Indian and Pakistani women li ving in the United States are lacking. This study contrasted breast cancer risk factors [serum total 17 beta-estradiol (E-2), sex hormone-binding glob ulin-bound E-2, available E-2, estrone (E-1), and dehydroepiandrosterone su lfate, reproductive history, family history of cancer, body composition/siz e, dietary intake, physical activity, and excretion of isoflavones] between two distinct ethnic groups of premenopausal women residing in the United S tares. We also determined the contribution of these and other factors to th e variability of each sex hormone. Distributions of values for serum total E-2, available E-2, and sex hormone-binding globulin-bound E-2 (%) were gre ater (p < 0.005) in American (n = 47) than in Indian and Pakistani (n = 47) women. Multiple regression analysis indicated that 26% of the variability (p less than or equal to 0.0001) in serum E-2 was accounted for by the rati o of total cholesterol to high-density lipoprotein cholesterol, length of t ime in the United States, and saturated fat intake, whereas less (17%) vari ability was accounted for by available E-2 (representing free E-2 + albumin -bound E-2), contributed by the ratio of total cholesterol to high-density- lipoprotein cholesterol and saturated fat intake. Five variables accounted for 31% of the variability (p less than or equal to 0.0001) in E-1. The maj or finding of this study was that circulating sex hormone concentrations we re determined more by environmental factors than by ethnicity, which was no t a significant contributor to any of the serum hormones.