Isoflavones and Postmenopausal WomenIsoflavones and Postmenopausal Women

To the Editor: I would like to raise some methodological concerns about the study by Dr Kreijkamp-Kaspers et al.¹ First, their assumption that soy isoflavones are equipotent to conventional hormone therapy is in error. Their power analysis indicates that they should have been able to detect a 6.7% increase in bone mineral density (BMD) based on 200 participants. They should have used 2-directional hypothesis testing and calculated power based on their actual sample size and, given that this magnitude of increase is within the range previously reported for bisphosphonates,² a 3% change in response to isoflavones over 1 year may have been more realistic. Second, the authors state that “adjustment for smoking history and baseline BMD did not change the results,” but current smoking status and antihypertensive medication use should have been taken into account statistically.

Third, those participants who had more recently transitioned through menopause experienced better results in both hip and spine BMD after 1 year of soy protein intake compared with the participants in the placebo group although the interaction was not statistically significant. This difference raises the possibilities that time since menopause was critically important in dictating a treatment effect or that the power of the study was insufficient for the subgroup analysis. Fourth, I am concerned about the impact of the 12 excluded vertebral scans on the study power. Finally, compliance based on supplement use by treatment group is important to report.