Isoflavones Lengthen Menstrual Cycle and May Help Prevent Breast Cancer
Menstrual Cycles

Richard J. Fehring
Reprint from Current Medical Research
Vol 15, No 1-2, Winter/Spring 2004
Washington, DC
Reproduced with Permission

One of the known risks of women developing breast cancer is the frequency of menstrual cycles over a lifetime and the proliferation of breast tissue during the luteal phase of the menstrual cycle. Women in modern developed countries have almost double the amount of menstrual cycles over a lifetime (either naturally or hormonally induced) than women from developing countries or women from earlier times. This is due to the greater number of pregnancies and the greater frequency of breast-feeding among women in developing countries and from earlier times. Both pregnancy and the practice of breast-feeding lower risks for breast cancer. It is also known that women in Japan and Asia have a much lower rate of breast cancer than women in developed western countries. A big reason for the lower Asian rates is dietary patterns (and in particular the use of soy products) and the increased length of their menstrual cycles. Soy products contain isoflavones that act as phytoestrogens, or, that is, weak estrogens. The estrogenic properties of the soy products in theory can help lengthen the follicular phase of the menstrual cycle.

Researchers at the University of South Florida tested this theory by investigating the effects of one of the major forms of isoflavones called genistein among 66 healthy premenopause, omnivorous women that ranged in age from 25 years to 55 years.1 The researchers conducted a double blind randomized study by randomly distributing the 66 women into two groups. One group received a soy product (i.e., 40 mg of genisten per day) for 12 weeks and the other group of women received a placebo over a 12-week period (or three menstrual cycles). The researchers measured dietary patterns (through a 4-day diet recall), menstrual cycle lengths (induding having the women participants utilize urinary LH tests kits to determine the follicular and luteal lengths of the cycles). The researchers also measured serum levels of estrone, estradiol, and serum hormone-binding globulin (SHBG) at baseline and at the end of the study.

The results showed that women participants who consumed the soy supplement for 3 menstrual cycles significantly increased their cycle length by a mean of 3.52 days and that the control group women decreased their mean length by 0.06 days from baseline to the third menstrual cycle. The mean follicular length of the soy supplement group increased a mean of 1.46 days compared to a decrease of 0.14 days for the women taking the placebo. The results also showed that SHBG increased by 41.4% in the soy group (as compared to 37.5% in the controls), free estradiol decreased 53.8% in the soy group (as compared to 37; 5% in the control) and estrone decreased 55.5% in the soy group (as compared to 42.8% in the control group). The authors concluded that the intake of the soy product influenced estrogen metabolism and menstrual cycle and follicular phase length. They also conduded that genisten intake is a potential means to reduce the risk for breast cancer. They indicated that this is an important finding, because an increase in menstrual cycle length would decrease the number of menstrual cycles over a lifetime, reduce the exposure of breast tissue to estrogen, and the breast tissue would spend more days in the follicular phase of the cycle when proliferation of breast tissue is at the lowest.


I liked this study for two reasons; one is that is was good from a scientific standpoint, in that the authors used a randomized double blind control group methodology. And two, it involved looking at how lifestyle (and in this case use of nutritional supplements) can effect the menstrual cycle and hormonal production. (Richard J Fehring)

1 Kumar, N.B., Cantor, A., & Allen, K., et al. The specific role of isoflavones on estrogen metabolism in premenopausal women. Cancer. 2002;94:1166-74. [Back]