Association between body mass index and rheumatoid arthritis: Exploring a possible role for alkaline phosphatase

Earlier studies linked body mass index (BMI) to rheumatoid arthritis (RA) onset. The role of serum alkaline phosphatase (ALP) in this equation is unclear. The aim of the study was to examine the association between BMI and RA in US adults and explore the possible contribution of ALP. Data from the NHANES 1999 to 2018 were analyzed. Weighted multivariate logistic regression models were leveraged to investigate the associations between BMI-RA, BMI-ALP, and ALP-RA. Restricted cubic spline curves were adopted to determine the relationships between BMI and RA and between ALP and RA. Finally, mediation analysis was implemented to examine the mediating role of ALP between BMI and RA risk. This analysis included 17,313 participants, among whom 1059 (6.1%) were diagnosed with RA. Through multivariate analysis, after adjusting for all confounders, a notable positive link was found between BMI and RA (OR = 1.038, 95% CI: 1.025-1.052). BMI was positively correlated with ALP (β = 0.272, 95% CI: 0.202-0.343, P <.001). ALP was positively associated with RA (OR = 1.004, 95% CI: 1.001-1.008, P = .028). Restricted cubic spline curves showed that both BMI-RA (nonlinear P-value = 0.197) and ALP-RA (nonlinear P-value = 0.315) exhibited linear positive correlations. Mediation analysis showed that ALP contributed to the association between BMI and RA, accounting for 5.97% of the total effect. Among a cohort of US adults, a higher BMI is positively associated with the risk of RA, and ALP may contribute to this association. However, future prospective cohort studies and mechanistic research are necessary to validate the potential role of ALP in the relationship between obesity and RA.