Vitamin B12 (Cobalamin)
Vitamin B12 deficiency in the post-bariatric surgery patient is multifactorial. Reduction in gastric acid production impairs the ability to cleave vitamin B12 from bound protein. Production of intrinsic factor is impaired; it is produced by parietal cells of the stomach and is necessary for absorption of vitamin B12 in the terminal ileum. Vitamin B12 deficiency symptoms include paresthesia of the hands and feet and may occur in spite of normal serum B12 levels. With the complex pathway of normal B12 absorption disrupted, bariatric surgery patients may utilize passive absorption of vitamin B12 by taking oral crystalline B12 (500-1000 pg daily) or intranasal B12 (500 pg weekly). If B12 levels fail to respond, intramuscular injection of 1000 pg/month may be used.
Calcium and Vitamin D
Calcium and vitamin D deficiencies are of particular concern following bariatric surgery and may cause secondary hyperparathyroidism with resulting negative effects on bone health. Preoperative obesity has been associated with substantially higher rates of vitamin D insufficiency and deficiency compared to the nonobese population .
Vitamin D deficiency or insufficiency should be treated with increased oral doses of vitamin D3. Significant deficiency (<20 ng/mL) may require treatment with 50,000 IU once a week for 8 weeks.
Calcium is preferentially absorbed in the duodenum and proximal jejunum. Absorption of calcium is dependent on adequate levels of vitamin D and an acidic environment which makes absorption especially problematic after the RYGB. In light of this, calcium citrate is recommended for improved absorption in a hypo or achlorhydric environment.
In the presence of decreased dietary intake or impaired absorption of calcium, normal blood calcium levels may be maintained through bone resorption of calcium and decreased urinary calcium excretion. Because of such compensatory responses, serum calcium alone is not a reliable indicator of calcium status and other laboratory measures should be assessed, such as 24 h urinary calcium, parathyroid hormone, and alkaline phosphatase.