Submitted to: Journal of Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/4/2009
Publication Date: 5/14/2009
Citation: Maskarinec, G., Verheus, M., Steinberg, F.M., Amato, P., Cramer, M.K., Lewis, R.L., Murray, M.J., Young, R.L., Wong, W.W. 2009. Various doses of soy isoflavones do not modify mammographic density in postmenopausal women. Journal of Nutrition. 139:981-986. Interpretive Summary: Many postmenopausal women are taking soy isoflavone pills because they are believed to reduce bone loss. However, the long-term safety of soy isoflavone pills on breast tissue is not known. The study was carried out to find out if taking soy isoflavone pills up to two years would have any harmful effect on breast tissues. A total of 406 healthy postmenopausal women took part in the study: one third of the women took 80 mg/day of soy isoflavones for two years, one third took 120 mg/day of soy isoflavones for two years, and the remaining one third took pills that do not contain any soy isoflavones for two years. Mammograms were taken on these women before and after one and two years of taking the pills. Density of the breast tissues were measured from the mammograms. The 2-year study showed that taking up to 120 mg/day of soy isoflavones for two years did not change the breast density in postmenopausal women.
Technical Abstract: 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. We 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, and placebo-controlled trial assigned 406 postmenopausal women to 80 or 120 mg/d of isoflavones each or a placebo for 2 y. Percent densities were assessed in digitized mammograms using a computer-assisted method. The mammogram reader did not know the treatment status and the time of mammograms. We applied mixed models to compare breast density by treatment while considering the repeated measures. The mammographic density analysis included 358 women, 88.2% of the OPUS participants; 303 had a complete set of 3 mammograms, 49 had 2, and 6 had only 1 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%/y across groups (P < 0.001). Stratification by age and BMI did not reveal any effects in subgroups. In this randomized 2-y trial, isoflavone supplements did not modify breast density in postmenopausal women. These findings offer reassurance that isoflavones do not act like hormone replacement medication on breast density.