Purpose: It is unknown whether there is an association between 25-hydroxyvitamin D (25(OH)D) level and thyroid disease in postmenopausal women with type 2 diabetes. This study aimed to evaluate the relationship between blood 25(OH)D levels and thyroid function in postmenopausal women with type 2 diabetes mellitus (T2DM).
Methods: This cross-sectional study involved Chinese postmenopausal women who presented to our diabetes clinic from March 2021 to May 2022 and were diagnosed with T2DM collected via a convenience sampling method. Blood samples were obtained from each patient to detect serum thyroid-stimulating hormone (TSH), triiodothyronine (T3), thyroxine (T4), free T3 (FT3), free T4 (FT4), thyroid peroxidase antibody (TPOAb), thyroglobulin antibody (TgAb) and 25(OH)D levels. Deficiency was defined as a 25(OH)D <  20 ng/mL. Comparative analysis was via t-test or chi-square test. Pearson correlation was then used to estimate the relationship between different thyroid function parameters and 25(OH)D. Multivariate logistic regression analysis was used to explore potential risk factors for 25(OH)D deficiency.
Results: In total, 157 out of 230 participants (68.26%) had 25(OH)D deficiency. Compared with patients with normal 25(OH)D levels, patients with 25(OH)D deficiency had shorter medical histories of diabetes mellitus (DM, p = 0.001) and higher rates of hyperthyroidism (p = 0.007), hypothyroidism (p < 0.001), TPOAb positive (p < 0.001) and TgAb positive (p < 0.001). Correlation analysis revealed that TSH (r = − 0.144, p = 0.030), FT4 (r = − 0.145, p = 0.029), TPOAb (r = − 0.216, p = 0.001) and TgAb (r = − 0.150, p = 0.024) levels were correlated with serum 25(OH)D levels. Further multivariable logistic regression analyses suggested that the length of DM history, presence of hyperthyroidism, presence of hypothyroidism and positive TPOAb were significantly associated with the presence of 25(OH)D deficiency in postmenopausal women with T2DM.
Conclusion: Hyperthyroidism, hypothyroidism and TPOAb positivity were significantly associated with the presence of 25(OH)D deficiency in postmenopausal women with T2DM.
Keywords: 25(OH)D, postmenopausal women, type 2 diabetes mellitus, thyroid disorder, thyroid peroxidase antibody, thyroglobulin antibody