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Shots of vitamin B12 are the preferred treatment for patients who develop a deficiency following bariatric surgery, researchers found.

In a review of the literature, the strongest evidence supported intramuscular B12 (cobalamin) in this population, while high-dose oral supplementation can be given to asymptomatic patients who've had only the Roux-en-Y gastric bypass (RYGB) procedure, Shounak Majumder, MD, of the University of Connecticut in Farmington, and colleagues reported online in the journal Surgery for Obesity and Related Diseases.

But they cautioned that "before objective efficacy data on high-dose oral vitamin B12, intranasal, or sublingual formulations become available, the intramuscular formulation should remain the preferred route of B12 supplementation in patients undergoing RYGB."

Nutritional deficiencies are a common problem following bariatric surgery. It is estimated that 9% to 14% of this population has vitamin B12 deficiency going into surgery, and the condition is exacerbated by malabsorption following the procedure.

The American Society for Bariatric and Metabolic Surgery has guidelines for monitoring and treating micronutrient deficiencies, but objective data on proper dose and route of administration is limited, the researchers said.

Thus they conducted a review of trials involving the prevention and management of vitamin B12 deficiency in patients having bariatric surgery.

Overall, they found that intramuscular B12 continues to be the "gold standard" of therapy for vitamin B12 deficiency in these patients, at a typical dose of 1,000 mcg per months.

"Given the long-term experience with the intramuscular formulation and its proven efficacy, we believe that it should remain the preferred route of administration for the immediate postoperative period after bariatric surgery, until stable serum levels are achieved," they wrote.

High-dose oral cyanocobalamin, a B12 supplement, can be considered in select patients with asymptomatic B12 deficiency who've had RYGB, especially if there are concerns with adherence to intramuscular therapy or other compliance issues, the researchers reported.

But they cautioned that the effectiveness of high-dose oral vitamin B12 therapy hasn't been extensively evaluated in patients having RYGB.

"The presence of gastric mucosal atrophy, and possibly small intestinal mucosal atrophy, and accelerated food transit time in patients undergoing RYGB can potentially limit the effective absorption of vitamin B12 and can result in treatment failure," they wrote.

Their review also found that patients having procedures such as sleeve gastrectomy or gastric banding may be maintained postoperatively on a lower dose of daily vitamin B12 supplementation.

"Although definite recommendations are not currently available for patients undergoing sleeve gastrectomy or gastric banding, oral supplementation at recommended daily allowance (RDA) appears to be sufficient to prevent postoperative B12 deficiency in this population," they wrote.

Majumder and colleagues warned that there is a lack of efficacy data on nasal and sublingual routes for maintenance therapy, which precluded recommendations about these strategies.

They concluded that bariatric surgery patients need continuous education on proper nutrition and the risk of developing nutrient deficiencies, particularly B12 deficiency.

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