Calcium absorption predominantly occurs in the duodenum and proximal jejunum and is dependent on vitamin D levels. Due to fat malabsorption, all fat-soluble vitamins (A, D, E and K) are at risk of deficiency among bariatric patients. Some investigators pointed out a deficient calcium intake and vitamin D deficiency after RYGB [60
]. Schafer et al. [61
] demonstrated that even patients with acceptable levels of vitamin D (≥ 30 ng/mL) and maintained under an adequate calcium intake (> 1200 mg/day) had a marked decrease in intestinal calcium absorption from 33% preoperatively to 7% after 6 months of RYGB. The common use of proton-pump inhibitors by bariatric patients may also affect calcium absorption contributing to the exacerbation of such deficiency [62
]. Clinical studies have also identified hypovitaminosis D in morbidly obese patients prior to RYGB [63
]. According to the Clinical Practice Guidelines for the Perioperative Nutritional, Metabolic, and Nonsurgical Support of the Bariatric Surgery Patient [65
], calcium supplementation should be at least 1200–1500 mg/day consisting of the usual consumption of calcium-rich foods like dairy products, seafood, almonds, green vegetables and other food items fortified with calcium. However, the consumption of milk and other dairy products have been associated with “Dumping syndrome” in some patients. The latter is due to the rapid emptying of food into the small intestine triggering rapid fluid shifts into the intestinal lumen and release of gastrointestinal hormones, causing gastrointestinal and vasomotor symptoms such as bloating, nausea, diarrhea, dizziness and sweating, among others [66
]. The natural sugar in dairy products (lactose) might worsen such symptoms which may appear soon after eating or later. Besides diet and especially for such patients, the use of adequate calcium supplements in the form of citrate salts is mandatory as gastric acid secretion might be reduced after BS averting the absorption of calcium carbonate. Furthermore, another advantage of calcium citrate supplementation is the reduction of urinary phosphate that, in association with the inhibitory effects of citrate, might protect against stone formation [67
]. In fact, a randomized, double-blind crossover study of RYGB patients, confirmed a better bioavailability of calcium citrate than calcium carbonate [68
]. The calcium bioavailability of a formulation of effervescent potassium calcium citrate after RYGB has been shown to be useful as well [69
]. Notably, hypercalciuria is not a frequent finding in post-BS patients [70
]. Nonetheless, taking the calcium supplements is preferable with meals, hence helping to prevent increases in urinary CaOx supersaturation. With respect to Vitamin D, a specific study in post-bariatric pregnant women reported that women after the first year of RYGB may present increased vitamin D demands compared to pregnant women who did not undergo surgery [71
]. According to the American guideline for BS, such patients should have nutritional surveillance and laboratory screening for deficiency every trimester [65
]. The minimal daily vitamin D supplementation for BS patients is at least 3000 international units (IU) until blood levels are greater than 30 ng/mL and in cases of severe vitamin D malabsorption, 50,000 UI for 1 to 3 times weekly to daily [65
]. The European Guideline also suggests a supplementation of 1200–1500 mg of elemental calcium (in diet and/or as citrate supplements in divided doses), and at least 3000 IU of vitamin D per day for post-BS patients [73
]. Regardless of the difficulties concerning the adequate intestinal absorption after BS, calcium supplementation and vitamin D repletion are essentially required to prevent both nephrolithiasis and bone disease.
In summary, the recommended amount of calcium intake after BS should be at least 1200–1500 mg/day, provided by diet or supplements and at least 3000 IU of Vitamin D per day adjusting to maintain adequate serum levels.