Soy Isoflavones Dont Increase Cancer Risk

BETHESDA, Md.Long-term supplementation with soy isoflavones is safe and does not cause increased risk for breast or endometrial cancer, according to the conclusions of the Osteoporosis Prevention Using Soy (OPUS) intervention study published in the American Journal of Clinical Nutrition.

The USDA-funded OPUS study was a multicenter, randomized, double-blind, placebo-controlled trial that followed 403 menopausal women for two years to assess the effects of daily supplementation with 80 or 120 mg aglycone equivalent soy hypocotyl isoflavones plus calcium and vitamin D.

At baseline and after one and two years, clinical blood chemistry values were measured and a well-woman examination was conducted, which included a mammogram and a Papanicolaou test. A cohort also underwent transvaginal ultrasound measurements to assess endometrial thickness and fibroids.

The baseline characteristics of the groups were similar. After 2 years of daily isoflavone exposure, all clinical chemistry values remained within the normal range. The only variable that changed significantly was blood urea nitrogen, which increased significantly after 2 years (P = 0.048) but not after 1 year (P = 0.343) in the supplementation groups. Isoflavone supplementation did anot affect blood lymphocyte or serum free thyroxine concentrations. No significant differences in endometrial thickness or fibroids were observed between the groups. Two serious adverse events were detected (one case of breast cancer and one case of estrogen receptor-negative endometrial cancer), which was less than the expected population rate for these cancers.

The findings concluded daily supplementation for 2 years with 80-120 mg soy hypocotyl isoflavones has minimal risk in healthy menopausal women.