Shiya Zeng,1,* Yanyue Tan,1,2,* Zhiwei Cao,3 Yunhao Zheng,1 Tiqian Liu,1 Yifei Deng,1 Xin Xiong1 

1State Key Laboratory of Oral Diseases & National Center for Stomatology & National Clinical Research Center for Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu, Sichuan, People’s Republic of China; 2Department of Nursing, West China Hospital of Stomatology, Sichuan University, Chengdu, Sichuan, People’s Republic of China; 3School of Stomatology, Tianjin Medical University, Tianjin, People’s Republic of China

*These authors contributed equally to this work

Correspondence: Xin Xiong, State Key Laboratory of Oral Diseases & National Center for Stomatology & National Clinical Research Center for Oral Diseases, West China Hospital of Stomatology, Sichuan University, No. 15, West Section 3, Second Ring Road, Chengdu, Sichuan, 610041, People’s Republic of China, Tel +86 028 85501425, Email drxiongxin@scu.edu.cn

Objective: Growing researches explore vitamin D’s role in temporomandibular disorders (TMDs), but the link between vitamin D and TMDs remains debated. To clarify the causal relationship, we conducted a Mendelian randomization (MR) analysis using data from genome-wide association studies (GWAS).
Subjects and Methods: The GWAS dataset of vitamin D (GWAS ID: ukb-d-30890_irnt; sample size: 329247) was obtained from the IEU Open GWAS project. And that of TMDs (GWAS ID: finn-b-TEMPORO; sample size: 134280), initiated on August 25th, 2017 and publicly released on December 18th, 2023, was extracted from the FinnGen dataset, whose cases were diagnosed based on the revised International Classification of Diseases, 10th Edition (ICD-10) code K07.6. Both datasets were obtained from the European population. According to three assumptions of MR analysis, a bi-directional MR analysis was performed to measure the causal relationship, with Inverse variance weighted (IVW) as the primary method and MR Egger and Weighted median as supplement. Moreover, diverse sensitivity analyses, including Cochran’s Q test, MR Egger intercept, Mendelian randomized polymorphism RESidual Sum and Outlier (MR-PRESSO), and leave-one-out analysis, were used to verify the stability of the findings.
Results: The MR analysis supported causal effects of vitamin D levels on TMDs risks within the European population using IVW method [odds ratio = 1.316; 95% confidence interval = 1.086 to 1.595; P = 0.005], supported by MR Egger and Weighted median. While there was no indication that TMDs have a direct impact on vitamin D levels [β: − 0.00738, standard error = 0.00665; P = 0.568].
Conclusion: The study revealed that within the European population higher levels of vitamin D led to higher risks of developing temporomandibular disorders, but found no obvious evidence that TMDs are causally associated with vitamin D. The conclusion should be cautiously interpreted, given the selection bias of TMDs patients sample.

Keywords: Mendelian randomization analysis, temporomandibular joint disorders, vitamin D, 25-hydroxyvitamin D