Background: Vitamin D deficiency is associated with glycemic dysregulation in many observational studies. However, the causality between them has not been fully established, especially in Asian origin. We used bidirectional Mendelian randomization (MR) analysis to explore the causal relationship between 25-hydroxyvitamin D [25(OH)D] and glycemic status and indices.
Methods: Participants were included from a survey in East China from 2014 to 2016 (10,338 and 10,655 participants having diabetes and vitamin D-related genotyping information). We calculated weighted genetic risk scores (GRS) as the instrumental variables for 25(OH)D concentration and diabetes based on related single nucleotide polymorphisms. Diagnosis of type 2 diabetes and prediabetes was based on American Diabetes Association criteria.
Results: The MR-derived odds ratios of genetically determined 25(OH)D for risk of type 2 diabetes (1565/10655) and prediabetes (3915/10655) was 0.985 (95% CI 0.940, 1.032) and 0.982 (95% CI 0.948, 1.016), respectively. The MR-derived estimates for fasting plasma glucose and HbA1c were also not significant. Moreover, the MR-derived regression coefficients of genetically determined diabetes and prediabetes for 25(OH)D was 0.448 (95% CI - 0.395, 1.291) and 1.303 (95% CI - 1.210, 3.816).
Conclusions: Our results support the conclusion that there is no causal association between vitamin D and type 2 diabetes and prediabetes using a bidirectional MR approach in a Chinese population.
Keywords: Mendelian randomization analysis; Prediabetes; Type 2 diabetes; Vitamin D.