Does vitamin D improve the serum level of anti-TPO and anti-TG in Autoimmune thyroid diseases? A systematic review and meta-analysis

Objective: We aimed to review and update data on the effectiveness of vitamin D on thyroid auto antibodies, anti-TPO and anti-TG in adults. Methods: Scopus and PubMed search engines were used up to February 2018 for clinical trials without any restriction in time and language. The outcome parameters were thyroid auto antibodies, anti-TPO and anti-TG. We included studies which reported aim parameters. Results were summarized as mean differences (MD) with 95% confidence intervals (CI). Effect sizes were pooled using random-effects models (the DerSimonian-Laird estimator). Results: Eight trials involving 526 subjects were included in this meta-analysis. Vitamin D supplementation did not significantly changed the serum level of anti-TPO (MD: -46.901 IU/mL, 95% CI: -111.841, 18.039, p=0.157) and anti-TG (MD: -0.903 IU/mL, 95% CI: -2.208, 0.401, p = 0.175) with high heterogeneity (I2= 77.1%, p= 0.000, I2= 26.5%, p= 0.253). Anti-TPO reduction was considerable in mixed-sex and low quality trials, doses of ≥ 1000 IU, periods of ≥ 2 months , AITD patients and in subjects with lower initial serum levels of vitamin D and higher initial serum level of anti-TPO (p <0.0001). Conclusions: Vitamin D supplementation did not improve the serum levels of anti-TPO and anti-TG. The effects of vitamin D supplementing on AITD should be further investigated by conducting larger sample size and well-defined trials of long enough duration.