Bariatric surgery is associated with a postoperative reduction of 25(OH) vitamin D levels (25(OH)D) and with skeletal complications. Currently, guidelines for 25(OH)D assessment and vitamin D supplementation in bariatric patients, pre- and post-surgery, are still lacking. The aim of this work is to analyse systematically the published experience on 25(OH)D status and vitamin D supplementation, pre- and post-surgery, and to propose, on this basis, recommendations for management. Preoperatively, 18 studies including 2,869 patients were evaluated. Prevalence of vitamin D insufficiency as defined by 25(OH)D < 30 ng/mL (75 nmol/L) was 85%, whereas when defined by 25(OH)D < 20 ng/mL (50 nmol/L) was 57%. The median preoperative 25(OH)D level was 19.75 ng/mL. After surgery, 39 studies including 5,296 patients were analysed and among those undergoing either malabsorptive or restrictive procedures, a lower rate of vitamin D insufficiency and higher 25(OH)D levels postoperatively were observed in patients treated with high-dose oral vitamin D supplementation, defined as ≥ 2,000 IU/daily (mostly D3-formulation), compared with low-doses (< 2,000 IU/daily). Our recommendations based on this systematic review and meta-analysis should help clinical practice in the assessment and management of vitamin D status before and after bariatric surgery. Assessment of vitamin D should be performed pre- and postoperatively in all patients undergoing bariatric surgery. Regardless of the type of procedure, high-dose supplementation is recommended in patients after bariatric surgery.

Osteosarcopenic obesity is a unique clinical condition where low bone and muscle mass coexist in individuals with obesity. Alterations in adipose tissue, skeletal muscle and bone are strictly interconnected, and vitamin D plays key roles in several metabolic pathways that are involved in maintaining musculoskeletal health and glucose homeostasis. We reviewed the available literature on mechanisms underlying osteosarcopenic obesity, with a focus on the role of vitamin D in the pathogenesis and treatment of the condition. We found that, although evidence from large observational studies and pre-clinical experiments strongly supports a role of vitamin D deficiency in the pathogenesis of osteosarcopenic obesity, the common belief that vitamin D improves musculoskeletal health lacks solid clinical evidence, as trials specifically aimed at assessing the effects of vitamin D supplementation in patients with osteosarcopenic obesity are not available, and trials that investigated the role of vitamin D on muscle and bone health in other patient populations either showed no or even detrimental effects. We conclude that large observational and interventional studies including individuals with osteosarcopenic obesity representative of different sex, age and race are needed to better define the role of vitamin D in the pathogenesis and treatment of this condition.

Luigi di Filippo, Andrea Giustina; Vitamin D deficiency and type 2 diabetes: the dangerous link between two modern pandemics, The Journal of Clinical Endoc