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Abstract
Background: Vitamin D is one of the most common micronutrient deficiencies in the obese population awaiting Roux-en-Y gastric bypass (RYGB) surgery and often persists post-operatively despite routinely recommended supplementation, suggesting there may be variable response to this supplementation. However, there are no established indicators that allow clinicians to identify the non-responders, and factors contributing to poor vitamin D repletion after surgery remain unclear. In addition, a patient's nutritional status is an important factor in postoperative morbidity and mortality after any major surgery, but it is unknown how vitamin D status impacts patient outcomes after bariatric procedures. The aims of this study were to identify the predictors of responsiveness to vitamin D supplementation in recipients of RYGB surgery, and to compare patient outcomes as measured by hospital readmissions and emergency room (ER) visits, between responders and non-responders in the year following surgery. Methods: The medical records of patients who underwent RYGB at the University of Washington Medical Center from 2009-2011 and had insufficient vitamin D concentrations (<30 ng/mL) at baseline were reviewed. Non-responders were defined as those who maintained serum 25(OH)D concentrations <30 ng/mL after 1 year; responders were those whose concentrations increased to >30 ng/mL after 1 year. Demographic, anthropometric and clinical variables were compared between the two groups to identify predictors. The number of readmissions and ER visits in the year following surgery were also compared between non-responders and responders. Results: There were 40 total patients; 15 non-responders and 25 responders. Baseline serum albumin concentrations were significantly higher in responders than non-responders (3.8±0.2 g/dL vs 3.5±0.2 g/dL, p=0.001). Hospital readmissions did not vary significantly between groups, but non-responders had significantly more ER visits in the year following surgery than responders (1 vs. 0, p=0.021). Both baseline serum albumin (OR=1.70, 95%CI=1.18-2.46, p=0.005) and ER visits (OR=0.37, 95%CI=0.15-0.91, p=0.031) were found to be a predictor of being a responder post-RYGB in the unadjusted logistic regression analysis; after adjusting for age, sex, baseline 25(OH)D, season, comorbidities, baseline serum albumin, BMI and weight, 1 year weight loss and serum albumin, # of ER visits, only baseline serum albumin remained a significant predictor (OR=2.19, 95%CI=1.15-4.17, p=0.016). Conclusions: Serum albumin at baseline was a potential predictor of response to vitamin D supplementation following RYGB in a population with insufficient vitamin D concentrations at baseline residing in the Pacific Northwest. There was a significant difference in the effect of season on 1 year serum 25(OH)D concentrations between responders and non-responders, while supplement use did not significantly differ between non-responders and responders. Non-responders also sought treatment at an emergency room significantly more than responders in the year following surgery. These predictors may allow clinicians to better identify and tailor supplement dosages to avoid or correct preexisting vitamin D deficiency after Roux-en-Y gastric bypass.
