Clinical Question: Do isoflavones improve cognitive function, bone mineral density, and plasma lipid levels in postmenopausal women?

Setting: Outpatient (any)

Study Design: Randomized controlled trial (double-blinded)

Allocation: Uncertain

Synopsis: Recent trials have not shown a benefit of postmenopausal estrogen in improving cognitive function, reducing cardiovascular complications, or maintaining long-term protection against fractures. In this trial, the authors evaluated whether naturally occurring plant isoflavones (phytoestrogens) could be an effective alternative for traditional estrogen therapy.

Approximately 200 healthy postmenopausal women 60 to 75 years of age were assigned in a double-blind fashion to receive 25.6 g of soy protein containing 99 mg of isoflavones (52 mg genistein, 41 mg daidzein, and 6 mg glycetein) or matching placebo on a daily basis for 12 months. Although not specifically stated in the manuscript, contact with the authors clarified that outcomes were assessed by persons blinded to treatment group assignment. Follow-up was complete for 86 percent of the original participants. Use of intention-to-treat analysis, cognitive function, bone mineral density, and plasma lipid levels did not differ significantly between the groups. The study had an 80 percent power to detect an improvement difference of 13 percent between the groups on the cognitive function test.

Bottom Line: Postmenopausal supplementation with soy protein containing isoflavones does not improve cognitive function or affect bone mineral density or plasma lipid levels. Previous studies evaluating an effect of isoflavones on postmenopausal hot flushes also have found minimal benefit. (Level of Evidence: 1b–)