The association between severity of vitamin D deficiency and Hashimoto's thyroiditis.

OBJECTIVE: The relation between vitamin D and autoimmune disorders has long been investigated regarding the important roles of this hormone in immune regulation. We evaluated 25-hydroxyvitamin D (25OHD) status in subjects with Hashimoto's thyroiditis (HT) and healthy controls.

METHODS: Group-1 included 180 euthyroid patients (123 females/57 males) with HT who were on a stable dose of L-thyroxine (LT). A total of 180 sex-, age-, and body mass index (BMI)-matched euthyroid subjects with newly diagnosed HT were considered as Group-2, and 180 healthy volunteers were enrolled as controls (Group-3). All 540 subjects underwent thyroid ultrasound and were evaluated for serum 25OHD, anti-thyroid peroxidase (anti-TPO), and anti-thyroglobulin (anti-TG) levels.

RESULTS: Group-1 had the lowest 25OHD levels (11.4 ± 5.2 ng/mL) compared to newly diagnosed HT subjects (Group-2) (13.1 ± 5.9 ng/mL, P = .002) and to control subjects (15.4 ± 6.8 ng/mL, P<.001). Serum 25OHD levels directly correlated with thyroid volume (r = 0.145, P<.001) and inversely correlated with anti-TPO (r = -0.361, P<.001) and anti-TG levels (r = -0.335, P<.001). We determined that 48.3% of Group-1, 35% of Group-2, and 20.5% of controls had severe 25OHD deficiency (<10 ng/mL). Female chronic HT patients had the lowest serum 25OHD levels (10.3 ± 4.58 ng/mL), and male control subjects had the highest (19.3 ± 5.9 ng/mL, P<.001).

CONCLUSIONS: We demonstrated that serum 25OHD levels of HT patients were significantly lower than controls, and 25OHD deficiency severity correlated with duration of HT, thyroid volume, and antibody levels. These findings may suggest a potential role of 25OHD in development of HT and/or its progression to hypothyroidism.