Phytoestrogen supplement use by women.

Phytoestrogens are weak estrogens found concentrated in soybeans. Americans consume phytoestrogens primarily in traditional soy foods, soymilk and isolated soy protein added during food processing or consumed as a beverage. Extracted phytoestrogens are also marketed in numerous forms as dietary supplements regulated under the Dietary Supplement Health and Education Act. Consumers of phytoestrogen supplements tend to be peri- and postmenopausal women looking for an alternative to hormone therapy. Although there are no approved health claims for phytoestrogens at this time, numerous claims are being made regarding benefits to heart, bone, breast and general menopausal health. The data supporting these claims are generally not strong. The strongest data show that phytoestrogens reduce the number and intensity of hot flashes, although the reduction is a modest 10-20%. The studies showing cholesterol lowering have used soy protein rather than phytoestrogen extracts. The soy protein appears to be required for this effect, although phytoestrogen extracts may have other beneficial effects on the cardiovascular system. The data on bone metabolism are suggestive of possible benefits whereas the effects on the breast are the most poorly understood. Although most animal studies have shown cancer-preventive effects, a few recent studies suggest that soy phytoestrogens may stimulate breast cancer cell growth under certain circumstances. Before recommendations regarding phytoestrogen supplements can be safely made, we must have more information on the effects of the extracts on bone, heart and breast health. Until safety with respect to breast cancer is established, phytoestrogen supplements should not be recommended, particularly for women at high risk of breast cancer.