Bone Response to Soy Isoflavones in Women
Condition: Osteopenia; Osteoporosis
MeSH terms: Osteoporosis; Bone Diseases, Metabolic
Study type: Interventional
Phase: Phase 2

Summary: 
      This study will provide valuable data on whether soy isoflavones impact bone loss in
      postmenopausal women. The study will help clarify potential mechanisms and contribute to our
      understanding of isoflavones as an alternative to traditional hormone therapy.
    

Detailed description: 
      Soy protein, rich in isoflavones (estrogen-like compounds), has been shown to prevent bone
      loss in ovariectomized rats. Short-term preliminary study results in perimenopausal women
      suggest a bone-sparing effect. Great interest in isoflavones as an alternative to hormone
      replacement therapy has emerged, yet the long-term efficacy of isoflavones on bone in humans
      is unknown. Our objective is to determine the three-year efficacy of isoflavone-rich soy
      extract in attenuating bone loss in postmenopausal women. The central hypothesis is that soy
      isoflavones will attenuate bone loss in these women by maintaining bone formation, which is
      modulated by growth factors and isoflavone metabolism. The rationale for this research is
      that current hormone therapy is fraught with adverse side effects, resulting in
      non-compliance. This randomized, double-blind, placebo-controlled clinical trial will examine
      the effects of two doses (80 or 120 mg daily) of isoflavone-rich soy extract on bone in
      non-osteoporotic postmenopausal women (N=234). The specific aims of this study are: 1) to
      determine the bone-preserving effects of isoflavones on lumbar spine bone mineral density
      (BMD); 2) to relate treatment-induced changes in BMD to changes in biochemical markers of
      bone turnover; 3) to identify potential mechanisms by which isoflavones prevent or modulate
      bone loss by measuring endogenous estrogens, sex hormone-binding globulin, insulin-like
      growth factor-I (IGF-I), urinary minerals, serum 25(OH)vitamin D, plasma isoflavones and
      their metabolites, and customary intake of isoflavone-containing soy; and, 4) to ascertain
      the safety of isoflavone-rich soy extract. Postmenopausal women will be recruited at two
      sites (117 at Iowa, 117 at California). Random effects repeated measures analyses will be
      used to characterize change in BMD as the primary outcome, estimate treatment-induced
      effects, and depict change in markers of bone turnover in relation to BMD change. We will use
      intent-to-treat for the primary test, but also account for potential modulators (reproductive
      hormones, IGF-I, plasma isoflavones) that affect bone, as indicated in specific aim 3.
    

Intervention name(s): Soy isoflavones; Extract tablets
Intervention type(s): Dietary Supplement; Dietary Supplement
Intervention description(s): Soy isoflavones extracted from soy protein, compressed into tablets; three tablets taken daily; Extract from soy protein, but devoid of isoflavones; three tablets taken once daily
Allocation: Randomized
Intervention model: Parallel Assignment
Masking: Triple (Participant, Investigator, Outcomes Assessor)
Primary purpose: Prevention
Keywords: soy; isoflavones; alternative hormone therapy; bone loss