TPO and multinodular goiter: 25(OH)D: 25-hydroxyvitamin D; anti-TPO: anti-thyroid peroxidase; anti-Tg: anti-thyroglobulin; AITD: autoimmune thyroid disease; HT: Hashimoto’s thyroid disease; GD: Grave’s disease; VDS: vitamin D sufficient; VDD: Vitamin D deficient; PTC: papillary thyroid carcinoma; LMN: lymph node metastasis; ETE: extrathyroidal extension; FTC: follicular thyroid cancer; ATC: anaplastic thyroid cancer; MNG: multinodular nontoxic goiter; TSH: thyroid-stimulating hormone; T4: thyroxine; T3: triiodothyronine