Body Mass Index Protects Against Temporomandibular Disorders, Whereas Systemic Inflammation, Vitamin D, and Migraine Do Not: A Causal Inference Study
Miao Yu, Li DaiBackground and Objectives
Observational studies link temporomandibular disorders (TMDs) with body mass index (BMI), vitamin D, C‐reactive protein (CRP), and migraine but causal relationships remain unclear. This study aimed to assess the bidirectional causal effects between these factors and TMD using Mendelian randomization (MR).
Materials and Methods
We used publicly available GWAS summary statistics. TMD data were from FinnGen R13 (23,035 cases; 477,151 controls). Exposure data for BMI, vitamin D, CRP, and migraine were from UK Biobank, SUNLIGHT, CHARGE, and FinnGen. Inverse‐variance weighted (IVW) analysis was the primary method, with multiple sensitivity analyses and stratified MR.
Results
Higher genetically predicted BMI significantly reduced TMD risk (IVW: OR = 0.84, 95% CI: 0.79–0.89, p = 6.9 × 10 −8 ), with consistent dose–response gradients across BMI strata. No significant causal effects were found for vitamin D (OR = 1.00, p = 0.932), CRP (OR = 1.03, p = 0.502), or migraine (OR = 1.00, p = 0.653). Reverse MR found no causal effects of TMD on any factor.
Conclusions
Higher BMI protects against TMD, whereas vitamin D, CRP, and migraine do not causally influence TMD risk. These findings challenge the inflammation‐deficiency hypothesis and highlight the role of body composition in TMD.