Effect of low and high doses of vitamin D3 therapy on vitamin D3, antithyroid antibody and thyroid hormone levels in thyroid autoimmunity

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Aims: Vitamin D3 deficiency is more common in autoimmune thyroid diseases (AITD). Vitamin D3 supplementation in AITD is not questioned, but the required doses have been offered differently in several reports. This study attempts to provide a clinical answer as to what doses of vitamin D3 may be effective in AITD. Methods: Ninety-seven patients were included in the study: 44 with Hashimoto’s thyroiditis (HT), 26 with Graves ’disease (GD) and 27 controls. Serum vitamin D3, thyroid hormone and autoantibody levels against thyroid peroxidase (TPO) and TSH receptor were measured before and after treatment. Biochemical data were measured by a fully automated competitive chemiluminescence assay and presented as geometric mean(95% confidence interval). Results: Baseline vitamin D3 deficiency was detected in 22 out of 44 HT, 13 out of 26 GD and 19 out of 27 controls, and improved after vitamin D3 therapy. Vitamin D3 therapy significantly increased serum vitamin D3 levels in all patient groups [46.07(16.55-128.29) vs. 71.05(40.61-124.3) nmol/l, p<0.0001 for HT, 44.27(8.98-218.25) vs. 64.22(38.85-106.16) nmol/l, p<0.0207 for GD, and 39(15.57-97.73) vs. 59.32(27.27-129.03) nmol/l, p<0.0003 for controls]. The increass in vitamin D3 levels was found after low-dose vitamin D3 therapy (<7000 NE/week) in HT (p<0.0001) and controls (p<0.0002), but not in GD. The success of vitamin D3 therapy was dependent on high doses of vitamin D3 (>7000 NE/week) in GD, but levels were lower in Graves’ ophthalmopathy (p<0.0302). Anti-TPO antibody and TSH levels were decreased by low doses of vitamin D3 in HT, but FT4 and FT3 decreased, and TSH levels increased only by high doses in GD. Conclusion: The efficacy of vitamin D3 therapy was demonstrated in all patient groups. The greatest improvement in vitamin D3 status was seen in HT. A dose-dependency of vitamin D3 therapy was rather related to the improvement in GD.