Table 1.

Inclusion and exclusion criteria for eligibility of the study.

Inclusion criteria	Exclusion criteria
Age between 18 and 60 years	Currently using pharmacological (e.g., hormone replacement therapy) or supplementation treatment to influence VD metabolism
Caucasian ethnicity	Disease influencing calcium metabolism, polyendocrinopathy or autoimmune disease and other causes of secondary hyperparathyroidism∗
BMI >40 kg/m2 or 35–40 kg/m2 with obesity-associated comorbidity	History of cancer
Availability and willingness to comply with 18-month outpatient follow-up	Prior head or neck surgery
Availability and willingness to have blood samples tested for calcium, 25-hydroxy vitamin D, and PTH levels.	Prior abdominal or bariatric surgery
Availability to take oral supplements, if needed	Lack of calcium metabolism documentation
Normal preoperative renal function	Lost to follow-up

^∗Causes of secondary hyperparathyroidism according to Fraser [22]: (i) steroid therapy; (ii) patients overclothing; (iii) bisphosphonate therapy; (iv) osteolytic lesions; (v) diuretic therapy; (vi) previous acute pancreatitis; (vii) state of sepsis; (viii) chronic kidney disease and hypercalciuria; (ix) intake of drugs that interact with vitamin D (e.g., phenobarbital and phenytoin); and (x) use of antacids containing aluminum that interfere with phosphate absorption.