Association of Preoperative Serum 25-Hydroxyvitamin D with Longitudinal Body Mass Index After Bariatric Surgery-A Mediation Effect of Serum Albumin

Background The predictive ability of vitamin D for weight loss after bariatric surgery is not well-characterized. This prospective cohort study assessed the utility of preoperative serum 25-hydroxyvitamin D (25(OH)D) as a predictor of body mass index (BMI) at follow-up after bariatric surgery. Additionally, the mediation role of serum albumin was explored. Methods Patients scheduled for bariatric surgery were recruited from a single center. The final analyzed cohort consisted of 316 subjects (age, 40 +/- 10 years; 35.4% males; BMI, 42.6 +/- 7.2 kg/m(2)). The associations between preoperative 25(OH)D and baseline (pre-surgery) BMI or repeated measures of BMI collected at baseline, and 3-, 6-, and 12-month post-surgery were examined using linear regression or linear mixed model, respectively. The mediation effect of baseline albumin was evaluated using mediation analysis. Results Before surgery, 98.5% of patients had vitamin D insufficiency (25(OH)D < 30 mu g/L). Baseline BMI elevated progressively as severity of vitamin D insufficiency increased (P-trend = 0.025). Lower 25(OH)D levels were independently associated with higher preoperative BMI (coefficient, - 0.20; 95% CI, - 0.32 to - 0.08; P = 0.001) or less BMI reduction at follow-up (coefficient, - 0.15; 95% CI, - 0.25 to - 0.04; P = 0.007), after adjustment for baseline demographics, diabetes status, and/or surgical procedure. The association diminished after accounting for albumin, which emerged as a significant determinant (coefficient, - 0.61; 95% CI, - 0.83 to - 0.40; P < 0.001). Mediation analysis showed that reduced albumin explained 30% (P < 0.001) of the relationship between 25(OH)D and longitudinal BMI. Conclusions Lower preoperative 25(OH)D is associated with less BMI reduction over 1-year follow-up after bariatric surgery, potentially mediated by reduced serum albumin.