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Sir,

In the recent article by Myung et al.,1 showing a usefulness of soy intake in decreasing the risk of endocrine-related gynaecological cancer, the optimal amount of soy food intake for the prevention of endocrine-related gynaecological cancers remained undetermined. Of interest, dose-related effects of isoflavones on endometrial bleeding in perimenopausal and postmenopausal women have been evaluated. (Bleeding was not considered to be a result of isoflavone intake until an incidence of bleeding of 2% or more.)

  • • 
    0.20 g/day or 2 l of soy milk for 3 years was associated in a single case study with abnormal uterine bleeding with endometrial pathology.2,3
  • • 
    0.15 g/day for 5 years was associated with significantly higher endometrial hyperplasia.4
  • • 
    0.092 g/day of isoflavones for 6 months was associated with one of 19 (5%) cases of endometrial proliferation in women aged over 40 years with no period for the past year.5
  • • 
    0.080 g/day of total isoflavones was associated with three of 32 (9%) postmenopausal women aged 40–60 years presenting with endometrial activity.6
  • • 
    0.070 g/day of isoflavones for 12 months was associated with bleeding in eight of 395 (2%) postmenopausal women aged 45–65 years with no normal periods for at least 2 years.7
  • • 
    0.054 g/day of isoflavones for 2 years in 389 postmenopausal women yielded no endometrial hyperplasia or bleeding.8
  • • 
    0.050 g/day of isoflavones for 12 weeks in 177 postmenopausal women with an average age of 55 years yielded no endometrial hyperplasia.9

An intake of isoflavones of more than 0.070 g/day was associated with endometrial bleeding in postmenopausal women. Unfortunately, few products are currently labelled with their isoflavone content.

References

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  2. References
  • 1
    Myung S-K, Ju W, Yang N, Choi HJ, Kim SC. Soy intake and risk of endocrine-related gynaecological cancer: a meta-analysis. BJOG 2009;116:16971705.
  • 2
    Chandrareddy A, Muneyyirci-Delale O, McFarlane SI, Murad OM. Adverse effects of phytoestrogens on reproductive health: a report of three cases. Complement Ther Clin Pract 2008;14:1325.
  • 3
    Comment on Chandrareddy in Messina M. The endometrial effects of isoflavones: a discussion paper. Complement Ther Clin Pract 2008;14:2124.
  • 4
    Unfer V, Casini ML, Costabile L, Mignosa M, Gerli S, Di Renzo GC. Endometrial effects of long-term treatment with phytoestrogens: a randomized, double-blind, placebo-controlled study. Fertil Steril 2004;82:1458.
  • 5
    Balk JL, Whiteside DA, Naus G, DeFerrari E, Roberts JM. A pilot study of the effects of phytoestrogen supplementation on postmenopausal endometrium. J Soc Gynecol Investig 2002;9:23842.
  • 6
    Wolff LP, Martins MR, Bedone AJ, Monteiro IM. Endometrial evaluation in menopausal women after six months of isoflavones. Rev Assoc Med Bras 2006;52:41923.
  • 7
    Palacios S, Pornel B, Bergeron C, Chantre P, Nogales F, Aubert L, et al. Endometrial safety assessment of a specific and standardized soy extract according to international guidelines. Menopause 2007;14:100611.
  • 8
    D’Anna R, Cannata ML, Atteritano M, Cancellieri F, Corrado F, Baviera G, et al. Effects of the phytoestrogen genistein on hot flushes, endometrium, and vaginal epithelium in postmenopausal women: a 1-year randomized, double-blind, placebo-controlled study. Menopause 2007;14:64855.
  • 9
    Upmalis DH, Lobo R, Bradley L, Warren M, Cone FL, Lamia CA. Vasomotor symptom relief by soy isoflavone extract tablets in postmenopausal women: a multicenter, double-blind, randomized, placebo-controlled study. Menopause 2000;7:23642.