• vitamin D;
  • calcium absorption;
  • osteomalacia;
  • malabsorption;
  • bariatric surgery;
  • liver disease


Vitamin D and calcium are critical for skeletal health. Their absorption from the intestine is negatively impacted by a number of gastrointestinal diseases and surgical procedures, leading to osteoporosis and/or osteomalacia. Diseases of the liver can impact the metabolism of vitamin D to its circulating form, 25(OH)D, as well as the production of carrier proteins, albumin and vitamin D–binding protein, that may alter the delivery of 25(OH)D and its active metabolite 1,25(OH)2D to target tissues, including the skeleton, again leading to bone disease. The clinician evaluating a patient with apparent osteoporosis and vitamin D deficiency/ insufficiency needs to consider a gastrointestinal etiology. Similarly, the clinician evaluating a patient with a gastrointestinal disorder needs to evaluate that patient for vitamin D deficiency and bone disease. Treatment involves adequate vitamin D and calcium supplementation to achieve normal serum 25(OH)D, PTH, and serum and urine calcium levels.