Background: Isoflavones are soy-derived phytoestrogens that may influence bone remodeling differently according to age, sex, hormonal status, dosage, and metabolism. This study evaluated their effects on bone mineral density (BMD), bone mineral content (BMC), and bone turnover markers in children, adolescents, and adults to clarify their potential role in bone health and osteoporosis prevention.
Materials and Methods: In this systematic overview, PubMed, Scopus, Web of Science, the Cochrane Library, and Google Scholar were searched through December 2025 for meta-analyses and comparative studies of soy isoflavones reporting bone mineral outcomes or turnover markers. Quality was assessed using AMSTAR and Jadad scales; substantial heterogeneity required narrative synthesis.
Results: Eight studies, comprising six meta-analyses and two comparative trials, were included. Among postmenopausal women, isoflavone supplementation was generally associated with modest improvements in BMD at the lumbar spine, femoral neck, and total hip, along with favorable changes in bone-resorption markers, particularly pyridinoline and C-terminal telopeptide of type I collagen. Subgroup analyses suggested that effects may be greater at doses below 90 mg/day. However, effect estimates varied across syntheses, and no study demonstrated a reduction in fracture risk. In infants and children, soy-based formula was not associated with significant differences in BMC compared with control formulas. In adolescent boys, short-term isoflavone supplementation did not significantly affect bone turnover markers or growth-related outcomes, despite evidence of systemic isoflavone exposure.
Conclusion: Soy isoflavones may modestly preserve bone density in postmenopausal women as adjuncts but cannot replace established osteoporosis therapies. No skeletal benefits were evident in infants or adolescent boys, and evidence in populations remains limited. Future trials should assess fracture outcomes and account for equol-producer status.