Bariatric surgery can cause vitamin deficiencies in one of two ways: by reducing food intake or by causing malabsorption of vitamins. Sleeve gastrectomy is an example of the first way. Sleeve gastrectomies reduce stomach size, which reduces appetite and means the patient’s food intake decreases. This in turn means a reduced vitamin intake, so the patient ingests less vitamins than they did before surgery. Patients who already eat a diet low in vitamins are at more risk of vitamin deficiencies. This type of diet includes such as extrinsic sugar, potato chips, processed meats, cream, butter and soft drinks. The patient may have to change their diet as well as take vitamin supplements. The second way bariatric surgery causes vitamin deficiencies is malabsorption. Malabsorption of food is actually the aim of intestinal bypasses. It causes weight loss because the body absorbs less calories than before surgery. The risk of vitamin deficiencies is actually higher in procedures involving an intestinal bypass. This means that procedures like sleeve gastrectomy cause less vitamin deficiencies, because they leave the intestine unaffected.
The main vitamin deficiencies that occur in postoperative patients are vitamin B12, vitamin D, and fat-soluble vitamins. These deficiencies are described in more detail below.
The first vitamin deficiency this review will discuss is vitamin B12 (cobalamin). The cause of vitamin B12 deficiency in post-surgery patients is decreased stomach acid. Stomach acid helps release vitamin B12 from food, but bariatric surgery limits this function by weakening the stomach’s acidic environment. This means vitamin B12 deficiencies are common after bariatric surgery. According to a study in 1986, 33% of patients have a vitamin B12 deficiency after roux -en-Y gastric bypass.
However, the risk of B12 deficiency depends greatly on the type of bariatric surgery.
An additional finding was that patients developed B12 deficiencies even though they were supposed to take a daily supplement. So why did these patients still develop deficiencies? Perhaps the reason was that many patients did not actually take their supplements. Dolan et al. found that a fifth of patients did not take vitamin supplements, even though they had vitamin deficiencies Therefore, physicians should regularly assess post-surgery patients for compliance with vitamins supplementation.. Levels below <300pg/ml are subnormal for vitamin B12.
Another common deficiency after bariatric surgery is vitamin D deficiency. The researchers analysed 355 obese patients who had undergone a sleeve gastrectomy or roux-en-y gastric bypass. They found that four years after surgery, the 44% of sleeve gastrectomy patients and 51% of roux-en-y gastric bypass patients had a vitamin D deficiency. The next most common vitamin deficiency was for vitamin B-6; 4-17% of patients had a deficiency in B-6. Another study found that 51% of patients had vitamin D deficiency after a distal roux-en-y gastric bypass. These studies demonstrate the widespread prevalence of vitamin D deficiencies in post-surgery patients. This is One of Vitamin D’s main roles is to promote the absorption of calcium by the intestines. It also helps regulate cells and the immune system. Physicians should ensure that patients do not fall below the serum 25(OH) vitamin D range of 20ng/ml..
Deficiencies of the fat-soluble vitamins (A, E and K) are also common after bariatric surgery. They are particularly common after biliopancreatic diversions with duodenal switch . One study measured the serum level of fat-soluble vitamins in 170 patients, four years after their biliopancreatic diversion surgery. The study found that occurrence of vitamin E did not increase significantly after the surgery. However, the incidence of vitamin K deficiency increased by 68% after surgery, and the incidence of vitamin A deficiency increased by 69%.These findings clearly demonstrate the need for long-term nutritional monitoring of these vitamins. Physicians should regularly test post-surgery patients for vitamin A, E and K deficiencies.