Fig. 1

MR and cohort validation support an inverse association between intestinal Akk abundance and IVDD. a Schematic representation of the MR analysis workflow, including data sources, SNP selection criteria, and analysis pipeline. b Forest plot showing the effects of instrumental variables (IVs) on IVDD risk, with effect sizes and confidence intervals. c Scatter plot comparing MR results from multiple methods. d Schematic representation of the clinical sample collection protocol for human subjects. e Correlation analysis between age, IVDD Pfirrmann grade, and Akk relative abundance in human feces, with Pearson correlation coefficients indicated. n = 62. f qRT-PCR analysis of fecal Akk abundance in 6- and 21-month-old mice. n = 6 per group. Data are presented as mean ± SD. Statistical analysis was determined by Pearson correlation (e) or an unpaired Student’s t-test (f). OR odds ratio, CI confidence interval