Risk of Functional Disorders And/or Thyroid Autoimmunity and Its Association with 25OH Vitamin D and Magnesium Levels: A Population-Based Case-Control Study

Background/Objectives: It has been suggested that vitamin D and magnesium levels appear to be associated with an increased risk of functional disorders and/or autoimmune thyroid diseases (AITD). In this study, our objective was to evaluate whether 25OH vitamin D (25OH Vit-D) and/or magnesium (Mg) levels are associated with an increased risk of AITD and/or thyroid dysfunction. Methods: A population-based case-control study was conducted (n = 1028) (cases: n = 514; controls: n = 514). Blood concentrations of 25OH Vit-D, Mg, TSH, FT4, FT3, and thyroid autoantibodies (TPOAb, TgAb, and TRAb) were determined in the study participants. Results: The prevalence of goiter, hypothyroidism, and thyroid autoantibody positivity was significantly higher in women (among cases). No differences were found in the prevalence of other thyroid disorders or thyroid antibody positivity (among cases) based on sex or age. The prevalence of thyroid antibody positivity (specifically TPOAb and/or TgAb) was significantly higher in cases with 25OH Vit-D and/or Mg deficiency. The 25OH Vit-D level that best discriminated the highest frequency of AITD was 23.5 ng/mL [AUC: 0.665 (95% CI: 0.636–0.694, p< 0.001)]; while for Mg it was 1.8 mg/dL [AUC: 0.697 (95% CI: 0.668–0.725, p< 0.001)]. Conclusions: The results of our study suggest that low levels of 25OH Vit-D and/or Mg are associated with an increased risk of goiter, hypothyroidism, and AITD.