Objective: The aim of this study was to investigate vitamin D status by measuring serum 25(OH)D levels in euthyroid patients with Hashimoto's thyroiditis (HT) who lived and worked on the sunny island of Crete, Greece, and to evaluate whether vitamin D3 supplementation is beneficial for the management of HT patients with vitamin D deficiency.
Subjects and methods: We studied 218 HT patients, euthyroid Caucasian Cretan Greek citizens: 180 females and 38 males. Among these patients, 186 (85.3%) had vitamin D deficiency defined as serum 25(OH)D levels < 30 ng/mL. The mean age of all these 218 HT patients was 35.3 ± 8.5 years. The mean age of the 186 vitamin D deficient HT patients (173 females and 13 males) was 37.3 ± 5.6 years. The 186 vitamin D deficient HT patients received vitamin D3 (cholecalciferol, CF) orally, 1200-4000 IU, every day for 4 months aiming to maintain serum 25(OH)D levels ≥ 40 ng/mL. Anthropometric characteristics (height, weight, waist circumference), systolic and diastolic blood pressure, serum concentration of 25(OH)D, thyrotropin (TSH), free thyroxine (FT4), anti-thyroid peroxidase (anti-TPO), antithyroglobulin (anti-TG), calcium and phosphorus levels and thyroid and kidney sonographic findings were recorded and measured before and after CF administration.
Results: There was a significant negative correlation only between serum 25(OH)D levels and anti-TPO levels among all 218 HT patients. Also, anti-TPO levels were significantly higher in 186/218 vitamin D deficient HT patients compared to 32/218 HT patients with no vitamin D deficiency (364 ± 181IU/mL versus 115.8 ± 37.1IU/mL, P<0.0001). Supplementation of CF in 186 vitamin D deficient HT patients caused a significant decrease (20.3%) in serum anti-TPO levels. Although at the end of the 4 months period of the study body mass index (BMI), serum anti-TG and TSH levels decreased by 2.2%, 5.3% and 4% respectively, these differences were not significant. No changes in the sonographic findings were observed.
Conclusion: The majority (85.3%) of the Greek Caucasian patients with HT studied who lived and worked in Crete had low serum 25(OH)D levels inversely correlated with serum anti-TPO thyroid antibodies. After 4 months of CF supplementation in the 186 HT patients with vitamin D deficiency, a significant decrease (20.3%) of serum anti-TPO levels was found. These findings suggest that vitamin D deficiency may be related to pathogenesis of HT and that its supplementation could contribute to the treatment of patients with HT.