Marini H et al. (2007) Effects of the phytoestrogen genistein on bone metabolism in osteopenic postmenopausal women: a randomized trial. Ann Intern Med 146: 839–847

Hormone replacement therapy successfully reduces postmenopausal bone loss, but carries an increased risk of cancer and vascular events. Observational studies suggest that consumption of high amounts of phytoestrogens reduces osteoporosis risk. Genistein is a component of soya that is similar to 17β-estradiol, and might have protective effects against bone loss according to a number of small, short-term studies. Because of its differential affinity for estrogen receptors, genistein has greater activity in bone than in reproductive tissue. Marini et al., therefore, conducted a 2-year randomized trial of genistein versus placebo in 389 osteopenic postmenopausal women.

After 2 years, participants who received genistein (54 mg/day) had increased BMD at the femoral neck and lumbar spine (change, +0.035 g/cm2 and +0.049 g/cm2, respectively), whereas these values decreased in participants who received placebo (−0.037 g/cm2 and −0.053 g/cm2, respectively, P <0.001). Genistein use decreased urinary levels of markers of bone resorption and increased levels of markers of new bone formation compared with placebo. Genistein had no effect on endometrial thickness, and reduced the mean incidence of hot flashes per day compared with placebo (1.7 vs 3.9, P <0.001). Withdrawals due to adverse events totaled 37 (19%) in the genistein group compared with 15 (8%) in the placebo group (P = 0.002); all adverse events were gastrointestinal (constipation, dyspepsia, vomiting, and epigastric or abdominal pain).

The authors conclude that genistein improves BMD and bone-turnover marker levels in osteopenic postmenopausal women. Studies to assess the effect of genistein on bone fracture risk are warranted.