Soy isoflavone tablets don't prevent menopausal symptoms, bone loss

Daily supplementation with soy isoflavone tablets had no effect on menopausal symptoms or bone loss, a new study has indicated.

Researchers performed a single-center, randomized, placebo-controlled, double-blind, clinical trial to determine whether taking 200 mg of soy isoflavones daily would help prevent bone loss and menopausal symptoms in women 45 to 60 years of age who were within five years of menopause and had bone mineral density T scores of at least −2.0 in the lumbar spine or total hip.

Study participants were randomly assigned to receive daily soy isoflavone tablets, 200 mg, or placebo. The study's main outcome measure was change in bone mineral density (lumbar spine, femoral neck, total hip) at two years, while secondary outcomes assessed menopausal symptoms. The study results appear in the Aug. 8/22 Archives of Internal Medicine.

Two hundred forty-eight women were randomly assigned to receive soy isoflavones (n=122) or placebo (n=126). Of those, 23 (18.8%) in the soy isoflavones group and 43 (34.1%) in the placebo group were lost to follow-up, leaving 182 women who completed the study. Some of these 182 patients (11.2% in the soy isoflavone group and 15.6% in the placebo group) stopped taking the study drug but continued to participate in all or most outcome assessments. At two years, the authors found no significant differences in bone mineral density changes in women assigned to soy compared with those assigned to placebo (spine, −2.0% vs. −2.3%; total hip, −1.2% vs. −1.4%; femoral neck, −2.2% vs. −2.1%). Hot flashes (48.4% vs. 31.7%; P=0.02) and constipation (31.2% vs. 20.6%; P=0.06) were significantly more common in the soy group than in the placebo group, but no other menopausal symptoms or adverse events differed significantly.

The authors acknowledged that their study had a substantial dropout rate, significantly higher in the placebo group than in the soy isoflavone group, and that the relatively small bone loss in the control group might have made it difficult to detect a treatment effect, among other limitations. They concluded, however, that 200 mg of soy isoflavones taken daily did not affect bone loss or menopausal symptoms in this study population.

An accompanying invited commentary pointed out the lack of effect of soy isoflavones in other studies, including two recent meta-analyses, and noted that certain nonhormonal therapies such as gabapentin may be effective for symptom relief in some women. “Perhaps efforts should be directed away from the hope of a one-size-fits-all therapy for menopausal symptoms toward using existing treatments to target the symptoms that disturb patients most,” the commentary authors wrote.