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United States Department of Agriculture

Agricultural Research Service


Location: Children's Nutrition Research Center

Title: Clinical outcomes of a 2-y soy isoflavone supplementation in menopausal women

item Steinberg, Francene
item Murray, Michael
item Lewis, Richard
item Cramer, Margaret
item Amato, Paula
item Young, Ronald
item Barnes, Stephen
item Konzelmann, Karen
item Fischer, Joan
item Ellis, Kenneth
item Shypailo, Roman
item Fraley, J
item Smith, E
item Wong, William

Submitted to: American Journal of Clinical Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/23/2010
Publication Date: 2/1/2011
Citation: Steinberg, F.M., Murray, M.J., Lewis, R.D., Cramer, M.A., Amato, P., Young, R.L., Barnes, S., Konzelmann, K.L., Fischer, J.G., Ellis, K.J., Shypailo, R.J., Fraley, J.K., Smith, E.O., Wong, W.W. 2011. Clinical outcomes of a 2-y soy isoflavone supplementation in menopausal women. American Journal of Clinical Nutrition. 93(2):356-367.

Interpretive Summary: Soy isoflavones or plant hormones are believed to have health benefits. Many menopausal women are taking soy isoflavone tablets to prevent bone loss or to reduce hot flashes. Few small and short-term studies suggested that oral intake of soy isoflavones might be harmful. To find out if soy isoflavone supplementation might be harmful, 403 menopausal women were enrolled in a 2-year study where 1/3 of the women took 3 pills per day that provided 120 mg of soy isoflavones, 1/3 took 3 pills per day that provided 80 mg of soy isoflavones and the remaining 1/3 took 3 pills per day that contained no soy isoflavones. Clinical blood chemistries and a well-woman examination that included a mammogram and a Papanicolaou test were conducted on each woman before and after 1 year and 2 years of supplement. The results showed that daily supplementation with 80-120 mg of soy isoflavones for 2 years has minimal risk in healthy menopausal women.

Technical Abstract: Soy isoflavones are naturally occurring phytochemicals with weak estrogenic cellular effects. Despite numerous clinical trials of short-term isoflavone supplementation, there is a paucity of data regarding longer-term outcomes and safety. Our aim was to evaluate the clinical outcomes of soy hypocotyl isoflavone supplementation in healthy menopausal women as a secondary outcome of a trial on bone health. A multicenter, randomized, double-blind, placebo-controlled 24-mo trial was conducted to assess the effects of daily supplementation with 80 or 120 mg aglycone equivalent soy hypocotyl isoflavones plus calcium and vitamin D on the health of 403 postmenopausal women. At baseline and after 1 and 2 y, 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 y 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 y (P = 0.048) but not after 1 y (P = 0.343) in the supplementation groups. Isoflavone supplementation did not 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. Daily supplementation for 2 y with 80–120 mg soy hypocotyl isoflavones has minimal risk in healthy menopausal women.

Last Modified: 10/17/2017
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