Association between osteoporosis and arthritis: Results from the NHANES and Mendelian randomization study

Background This study seeks to investigate associations of osteoporosis (OP) with arthritis and to assess causality using Mendelian randomization (MR). Methods Firstly, an observational study was conducted using the National Health and Nutrition Examination Survey (NHANES). The relationship between OP and arthritis was analyzed by weighted multivariate logistic regression. Furthermore, a Mendelian randomization analysis was performed to examine the causal effect of arthritis on OP. Genetic data on OP and arthritis were derived from independent genome-wide association studies (GWAS). Arthritis includes osteoarthritis and inflammatory arthritis. The inverse variance weighting method was used to estimate causal effects. Sensitivity analyses were performed to further validate the robustness of the results. Results In this cross-sectional analysis, a positive association was found between OP and arthritis (OR = 1.758; 95% CI, 1.316-2.347; P < 0.01). These results did not change on multiple imputations (OR = 1.469, 95% CI, 1.044-2.068; P = 0.031 < 0.05). In MR analysis, it was found that OP was causally associated with rheumatoid arthritis (OR = 0.854; 95% CI, 0.736-0.992; P = 0.038 < 0.05), seropositive rheumatoid arthritis (OR = 0.998; 95% CI, 0.998-0.999; P < 0.001), ankylosing spondylitis (OR = 1.003; 95% CI, 1.000-1.005; P = 0.026 < 0.05), systemic lupus erythematosus (OR = 1.001; 95% CI, 1.000-1.001; P = 0.002 < 0.01), and gout (OR = 1.001; 95% CI, 1.000-1.001; P = 0.038 < 0.05) based on the IVW method. There was no causal association between OP and osteoarthritis, knee osteoarthritis, hip osteoarthritis, Spondyloarthritis, and seronegative rheumatoid arthritis. None of the analyses revealed any horizontal pleiotropy or heterogeneity. Conclusion In this cross-sectional study, a significant association is found between OP and arthritis. Additionally, the investigation using MR revealed evidence supporting a causal relationship between OP and certain types of arthritis.