Background: Bones and muscles are connected anatomically, and functionally. Preliminary evidence has shown the gut microbiome influences the aging process of bone and muscle in animal studies. However, such evidence in humans is still scarce. This study aimed to assess the microbiome-bone and microbiome-muscle associations in two cohorts of community-dwelling older adults. Methods: We leveraged information from two large population-based cohorts, i.e., the Rotterdam Study (mean age 62.7 (SD:5.6) years; n=1,249) and the Framingham Heart Study (mean age 55.2, (SD: 9.1) years; n=1,227). For individuals included in this study, gut microbiome 16S rRNA sequencing, musculoskeletal phenotyping derived from DXA images, lifestyle and socioeconomic data, and medication records were available. Per cohort, the 16S rRNA sequencing data, derived from stool, were processed with the DADA2 pipeline and taxonomies were assigned using the SILVA reference database. In addition, the microbiome functional potential was obtained with PICRUSt2. Further, we investigated the association between the human gut microbiome (alpha diversity, genera and predicted functional pathways) and appendicular lean mass (ALM), femoral neck bone mineral density (FN-BMD) and trabecular bone score (TBS) using multilinear regression models controlling for multiple confounders, and performed a joint analysis from both cohorts. Sex-stratified analyses were also conducted. Results: The gut microbiome alpha diversity was not associated with either tested phenotype after accounting for multiple-testing (P>1.67e-02). In the joint analysis, lower abundance of Oscillibacter (beta= -0.51, 95%CI [-0.74, -0.29]), Anaerotruncus (beta=-0.41, 95%CI [-0.61, -0.21]), Eisenbergiella (beta=-0.39, 95%CI [-0.59, -0.19]) and higher abundance of Agathobacter (beta=0.40, 95%CI [0.20, 0.60]) were associated with higher ALM (P<2.0e-04). Lower abundance of Anaerotruncus (beta=-0.32, 95%CI [-0.45, -0.19]), Hungatella (beta=-0.26, 95%CI [-0.38, -0.15]) and Clostridiales bacterium DTU089 (beta=-0.37, 95%CI [-0.55, -0.19]) was associated with higher ALM only in females (P< 2.0e-04). Moreover, the biotin biosynthesis II pathway was positively associated with ALM (beta=0.44, 95% CI [0.24, 0.64]) (P<1.90e-04) in females while no associations were observed in males. We did not observe any robust association of bone traits with gut microbiome features. Conclusion: Our results indicate that specific genera are associated with ALM in middle-aged and older adults and these associations can present in a sex-specific manner. Overall, our study suggests that the gut microbiome is linked to muscle aging in middle-aged and older adults. However, larger sample sizes are still needed to underpin the specific microbiome features involved.

The authors have declared no competing interest.

This study was funded by European UnionHorizon 2020 research and innovation program under Marie Skłodowska-Curie grant agreement No 860898.

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Medical Ethical Committee of Erasmus MC has approved this work. The Advarra Institutional Review Board has given approval for this work.

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