Exploring the Role of Onion Derived Polyphenols in Bone Health: A Systematic Review of In Vitro to Human Studies

Background: We evaluated certain factors relative to onion (Allium spp.) and onion-derived polyphenols. Methods: We searched PubMed, Scopus, and Google Scholar from 2010 to 20 October 2025 without language limits. Eligible designs comprised of in vitro, animal, and human studies assessing onion, onion extracts, or isolated onion-derived polyphenols with bone outcomes. Two reviewers independently screened, extracted, and assessed risk of bias (RoB 2 for RCTs; SYRCLE for animals). Results: We included X studies (a in vitro, b animal, and c human RCTs; N samples). In vitro limitations included the following: heterogeneous models, short human follow-up, small samples, and moderate-to-serious risk of bias in animals. Reports included improvements in bone mineral density (BMD), bone mineral content (BMC), bone turnover markers, and osteoclast/osteoblast activity. Onion extracts consistently inhibited RANKL-induced osteoclastogenesis while sparing osteoblast function. In animals, onion or quercetin/kaempferol preserved BMD and improved mineral content and (in several models) fracture healing. In one small RCT of onion juice (8 weeks), antioxidant status improved with a trend to attenuated BMD loss; a resveratrol RCT was excluded/included as a benchmark. Conclusions: Pre-clinical evidence suggests anti-resorptive and osteogenic effects of onion-derived polyphenols; human evidence is limited and characterized by low certainty. Longer RCTs are needed to define effective doses and clinical relevance.