Hypocalcemia is a frequent adverse event after thyroidectomy. It is usually related to hypoparathyroidism, but preoperative hypocalcemia, hypomagnesemia or vitamin D deficiency contributes to it. This study aims to determine the frequency of vitamin D deficiency or insufficiency in patients submitted to thyroidectomy, to define the risk attributed to vitamin D deficiency to postoperative hypocalcemia, to identify other factors associated to postoperative calcium disorder, and to evaluate the benefit of preoperative treatment of vitamin D deficiency to prevent postoperative hypocalcemia.

Subjects to be submitted to total thyroidectomy will be included in the study. The investigators will evaluate serum levels of total calcium, ionic calcium, phosphorus, magnesium, creatinine, albumin, alkaline phosphatase, fasting glucose, thyroid stimulating hormone (TSH), free thyroxin (FT4), intact parathyroid hormone (PTH), 25 hydroxy vitamin D (25OHD), osteocalcin, C-terminal telopeptide (CTX) and procollagen type 1 amino-terminal propeptide (P1NP). Patients will be randomized to 3 groups: (1) 30 subjects with 25OHD < 20 ng/mL that will receive 100,000U of cholecalciferol weekly for 4 weeks before surgery, (2) 30 subjects with 25OHD < 20 ng/mL that will not receive cholecalciferol before surgery and (3) 30 controls with 25OHD >= 20 ng/mL that will not receive cholecalciferol before surgery. Afterwards, the investigators will evaluate immediate postoperative PTH and measure serum levels of total calcium, ionic calcium, magnesium, alkaline phosphatase, osteocalcin, CTX and P1NP in first and second postoperative days for further analysis.

Inclusion Criteria:

• patients that will be submitted to total thyroidectomy

Exclusion Criteria:

• < 18 year-old
• chronic renal failure (creatinine > 1.5 mg/dL)
• fasting glucose > 200 mg/dl
• albumin < 3.5 g/L
• preoperative use of calcium supplements, bisphosphonates, corticosteroids