BACKGROUND

Observational studies and small trials of short duration suggest that the isoflavone phytoestrogen genistein reduces bone loss, but the evidence is not definitive.

OBJECTIVE

To assess the effects of genistein on bone metabolism in osteopenic postmenopausal women.

DESIGN

Randomized, double-blind, placebo-controlled trial.

SETTING

3 university medical centers in Italy.

PATIENTS

389 postmenopausal women with a bone mineral density (BMD) less than 0.795 g/cm2 at the femoral neck and no significant comorbid conditions.

INTERVENTION

After a 4-week stabilization period during which participants received a low-soy, reduced-fat diet, participants were randomly assigned to receive placebo (n = 191) or 54 mg of genistein (n = 198) daily for 24 months. Both the genistein and placebo tablets contained calcium and vitamin D.

MEASUREMENTS

The primary outcome was BMD at the anteroposterior lumbar spine and femoral neck at 24 months. Secondary outcomes were serum levels of bone-specific alkaline phosphatase and insulin-like growth factor I, urinary excretion of pyridinoline and deoxypyridinoline, and endometrial thickness. Data on adverse events were also collected.

RESULTS

At 24 months, BMD had increased in genistein recipients and decreased in placebo recipients at the anteroposterior lumbar spine (change, 0.049 g/cm2 [95% CI, 0.035 to 0.059] vs. -0.053 g/cm2 [CI, -0.058 to -0.035]; difference, 0.10 g/cm2 [CI, 0.08 to 0.12]; P < 0.001) and the femoral neck (change, 0.035 g/cm2 [CI, 0.025 to 0.042] vs. -0.037 g/cm2 [CI, -0.044 to -0.027]; difference, 0.062 g/cm2 [CI, 0.049 to 0.073]; P < 0.001). Genistein statistically significantly decreased urinary excretion of pyridinoline and deoxypyridinoline, increased levels of bone-specific alkaline phosphatase and insulin-like growth factor I, and did not change endometrial thickness compared with placebo. More genistein recipients than placebo recipients experienced gastrointestinal side effects (19% vs. 8%; P = 0.002) and discontinued the study.

LIMITATIONS

The study did not measure fractures and had limited power to evaluate adverse effects.

CONCLUSION

Twenty-four months of treatment with genistein has positive effects on BMD in osteopenic postmenopausal women. ClinicalTrials.gov registration number: NCT00355953.