Vitamin D and the bariatric surgical patient: a review

Adiposity has been inversely associated with vitamin D concentration across a range of body mass index values and cultural groups. As obesity has increased markedly worldwide, a greater number of patients with severe obesity have been treated with gastric restrictive and/or malabsorptive surgical procedures. The purpose of this review was to describe current knowledge about vitamin D and severe obesity, and the impact of obesity surgery on vitamin D status.

A systematic review was conducted with search terms obesity, vitamin D, osteoporosis, bone disease, gastric bypass, and obesity surgery in various combinations. Publications were limited to those since 2000 to control for similarity in vitamin D assays and obesity prevalence levels.

Mean 25-hydroxy vitamin D was <80 nmol/l in more than 1,900 patients preoperatively, and was not restored to the optimal concentration of >80 nmol/l postoperatively. Both secondary hyperparathyroidism and bone loss were common, particularly when the obesity surgery included a malabsorptive component. Standard postsurgical supplementation with vitamin D and calcium have not been adequate to suppress secondary hyperparathyroidism or to restore 25-hydroxy vitamin D status.

The mechanisms behind vitamin D deficiency in severe obesity and evidence-based corrective actions have not been well-defined. Of particular concern are adolescents who qualify for and elect surgical treatment of their obesity, where subsequent metabolic bone disease may be long-standing.