Effects of vitamin D in thyroid autoimmune pathologies: literature review and own data

Abstract

Background. Vitamin D (VD) is a versatile steroid hormone that regulates the activity of several thousand genes. Over the past decades, numerous diseases associated with VD deficiency have been reported, including cancer and autoimmune thyroid disorders. Researches revealed that VD can influence the development and course of these diseases. The VD participation in modulation of the hypothalamus-pituitary-thyroid gland axis, both at the level of the pituitary gland and at that of the thyroid, has been shown. The effect of VD on autoimmune diseases, including thyroid autoimmune diseases, is widely studied. Most of the existing data support the relationship between VD deficiency and a greater tendency to develop and higher antibody titers associated with Hashimoto’s thyroiditis, Graves’ disease (GD) and postpartum thyroiditis. An important fact is that epidemiological studies have demonstrated a high prevalence of VD deficiency or insufficiency throughout the world. VD insufficiency is a potent dietary trigger that results in severe, chronic diseases. The question arises how reliable is the relationship between VD and autoimmune thyroid diseases (AITD). Although the results of the studies performed are somewhat contradictory, the vast majority of data indicates a link between VD deficiency and an increased risk of developing the disease, high antibody titers, and difficulties in treatment. Genetic polymorphisms associated with VD function and metabolism also have some influence on the risk of ATD. With regard to the precise nature of the relationship between VD and AITD, it is believed that VD plays a small but significant role in the AITD pathogenesis. After the AITD development, its consequence may be an increase in VD deficiency. It is the need to determine the effect of VD supplementation in the prevention and treatment of AITD and its optimal level directly for clinical practice. It is necessary for clinical practice to determine the effect of VD supplements in the prevention and treatment of AITD and its optimal level. A study, the purpose of which was to study the content of VD, namely 25(OH)D in 176 patients with GD complicated by autoimmune ophthalmopathy (AO) and to identify a correlation relationship with antithyroid antibodies (TPO, TSHR-Ab) was carried out at the State Institution “V.P. Komissarenko Institute of Endocrinology and Metabolism of the National Academy of Medical Sciences of Ukraine”. Materials and methods. The levels of 25(OH)D, TSH, TSHR-Ab, TPO were determined by enzyme immunoassay using standard kits from Siemens firm. During the study, 176 patients were divided into two groups, depending on the presence of AO: the first group consisted of patients with GD without AO (62 people), the second group included patients with GD and AO (114 people). Results. In GD, 91.78 % of patients (161 people) have an insufficient level of 25(OH)D content: a suboptimal level was recorded in 42 patients (23.86 %), and a deficit — in 119 patients (67.61 %). A significant negative correlation relationship was revealed between TSHR-Ab and 25(OH)D in the group of patients with GD and AO — with a lower level of 25(OH)D, the higher values of TSHR-Ab correlate. Compensation of the 25(OH)D deficiency leads to a significant (P< 0.05) decrease in the levels of TSHR-Ab and TPO in patients with GD. Besides, there is a large body of literature available lin-king vitamin D to thyroid autoimmunity as a result of cross-sectional studies and observations. Conclusions. Thus, there is still an urgent need for large multicenter studies to evaluate the effect of vitamin D supplementation on meaningful long-term clinical endpoints in AITD.