Vitamin D deficiency is not associated with early stages of thyroid autoimmunity.

Context: Vitamin D deficiency has been identified as a risk factor for a number of autoimmune diseases including type 1 diabetes and multiple sclerosis.
Objective: We hypothesized that low levels of vitamin D are related to the early stages of autoimmune thyroid disease (AITD).
Design: Two case-control studies were performed. In the cross-sectional study A, euthyroid subjects with genetic susceptibility for AITD but without thyroid antibodies were compared with controls. Cases were subjects from the Amsterdam AITD cohort (euthyroid women who had first- or second-degree relatives with overt AITD) who at baseline had normal TSH and no thyroid antibodies; controls were healthy women examined at the same period. In the longitudinal study B, subjects who developed de novo thyroid peroxidase antibody (TPO-Ab) were compared with those who did not. Cases and controls were subjects from the Amsterdam AITD cohort who at baseline had normal TSH and no thyroid antibodies and during follow-up developed TPO-Ab (cases) or remained without thyroid antibodies (controls). Controls in both studies were matched for age, BMI, smoking status, estrogen use, month of blood sampling, and in study B for the duration of follow-up.
Results: Serum 25(OH)D levels were as follows: study A: 21.0 ± 7.9 vs 18.0 ± 6.4 ng/ml (78 cases vs 78 controls, P=0.01); study B: baseline, 22.6 ± 10.3 vs 23.4 ± 9.1; follow-up 21.6 ± 9.2 vs 21.2 ± 9.3 ng/ml (67 cases vs 67 controls, NS).
Conclusions: Early stages of thyroid autoimmunity (in study A genetic susceptibility and in study B development of TPO-Ab) are not associated with low vitamin D levels.