Natto for Bone Health

Research suggests that regular natto consumption is associated with improved bone health outcomes, particularly through its exceptionally high content of vitamin K2 (as MK-7), which appears to support the activation of osteocalcin and the maintenance of bone mineral density. The evidence base includes a 2025 meta-analysis of over 2,300 Japanese participants, several cross-sectional and observational studies in Japanese men and women, a five-year longitudinal study linking natto intake to reduced bone loss and tooth retention, and a one-year randomized controlled trial in premenopausal women that found favorable shifts in bone turnover markers but no statistically significant change in bone stiffness — reflecting the mixed picture that emerges from the literature. Reviews from 2005 and 2009 similarly characterize the overall evidence as promising but not yet conclusive, noting that isoflavones and calcium in soy foods may also contribute alongside vitamin K. Importantly, most studies were conducted in Japanese populations accustomed to natto consumption, the majority of evidence is observational rather than experimental, and the 2025 meta-analysis rates the certainty of evidence as moderate to very low, meaning these findings may not generalize broadly and should not be interpreted as establishing a definitive causal relationship.