The relationship between subclinical hypothyroidism and vitamin D

Abstract

Aim: Vitamin D (vitD) is primarily responsible for bone formation and mineralization. However, in recent years, it has been suggested that vitD may play a role as an immune modulator in the development of numerous diseases, including autoimmune diseases. It has been observed that there is an association between chronic autoimmune thyroiditis (AIT) and vitD levels. This study aims to investigate whether there are differences in the levels of 25-hydroxy vitamin D [25(OH)D], calcium, and phosphorus in patients with subclinical hypothyroidism (SCH) due to AIT, in patients with antibody-negative subclinical hypothyroidism (ANSCH), and in healthy control subjects. Material and Method: Data from 50 newly diagnosed patients with SCH (35 of whom AIT) and 50 euthyroid and antibody-negative healthy controls who presented to the Department of Endocrinology and Internal Medicine at our hospital between 2018 and 2020 were retrospectively reviewed. Calcium, phosphorus, and 25(OH)D levels of patients and controls were compared. Results: Serum 25(OH)D levels were significantly lower in patients compared to controls (16.2±7.8 ng/ml and 20.4±8.2 ng/ml, respectively; p=0.024). Serum levels of calcium (p=0.081) and phosphorus (p=0.712) did not differ between groups. In a subgroup analysis, patients with AIT had significantly lower 25(OH)D values than controls (p=0.009). Compared to controls, 25(OH)D levels were comparable in the ANSCH group (p=0.096). 25(OH)D level was higher in the AIT group than in the ANSCH group (p=0.01). Conclusion: Our results show that patients with SCH have lower 25(OH)D levels than healthy controls. However, this difference is significant in patients with AIT. It is recommended to screen for vitD deficiency in patients with SCH due to AIT.