Soy Doesnt Modify Breast Density

HONOLULU—Current findings from a study at the Cancer Research Center of Hawaii offers reassurance that isoflavones do not act like hormone replacement medication on breast density (J Nutr. 2009;139(5):981-86). Soy isoflavones have functional similarity to human estrogens and may protect against breast cancer as a result of their antiestrogenic activity or increase risk as a result of their estrogen-like properties. Researchers examined the relation between isoflavone supplementation and mammographic density, a strong marker for breast cancer risk, among postmenopausal women. The Osteoporosis Prevention Using Soy (OPUS) study, a multi-site, randomized, double blinded, placebo-controlled trial assigned 406 postmenopausal women to 80 or 120 mg/d of isoflavones each or a placebo for two years. The mammographic density analysis included 358 women, 88.2 percdent of the OPUS participants; 303 had a complete set of three mammograms, 49 had two and six had only one mammogram. At baseline, the groups were similar in age, BMI and percent density, but mean breast density differed by study site (P=0.02). A model with all mammograms did not show a treatment effect on any mammographic measure, but the change over time was significant; breast density decreased by 1.6 percent/year across groups (P<0.001). Stratification by age and BMI did not reveal any effects in subgroups. In this randomized two-year trial, isoflavone supplements did not modify breast density in postmenopausal women.