Parathyroid hormone (PTH) is found to be elevated in morbid obesity due to the defective hepatic metabolism of vitamin D. Bariatric surgery is performed to help patients with BMI>40 kg/m2 to effectively lose weight, particularly in patients with obesity who are afflicted with complications such as NAFLD/NASH. Here, PTH is linked to obesity due to melanocortin 4 receptor deficiency.