More information on the effects of phytoestrogens on bone, heart and breast health is needed before recommendations on supplementation can be safely made, argues a report in this month's issue of the Journal of Nutrition.
Extracted phytoestrogens marketed in numerous forms as dietary supplements have gained increasing attention as an alternative to hormone therapy for peri- and postmenopausal women. Phytoestrogens have been linked to benefits for heart, bone, breast and general menopausal health, but the data supporting these claims are "generally not strong", writes Mindy S. Kurzer from the Department of Food Science and Nutrition at the University of Minnesota in the US.
The strongest data show that phytoestrogens reduce the number and intensity of hot flushes, although the reduction is a modest 10-20 per cent, argues Kurzer. Indeed supplements containing a soy compound were no better than a placebo at relieving the symptoms of menopause, according to a Finnish study published in this month's Obstetrics and Gynecology journal.
The studies showing cholesterol lowering effects have used soy protein rather than phytoestrogen extracts, says Kurzer. The soy protein appears to be required for this effect, although phytoestrogen extracts may have other beneficial effects on the cardiovascular system, the researcher writes.
Kurzer also discusses the data on bone metabolism. These 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, she notes.
"Until safety with respect to breast cancer is established, phytoestrogen supplements should not be recommended, particularly for women at high risk of breast cancer," concludes Kurzer.
Her findings should spur researchers and the industry on to find the necessary scientific support to make health claims for these plant chemicals which could have significant potential to promote health.