Associations of postoperative vitamin D with body composition changes after bariatric surgery: a prospective cohort study

Objective To clarify associations between vitamin D and body composition in individuals with obesity after bariatric surgery, and explore the predictive value of preoperative vitamin D for postoperative body composition. Methods A total of 113 individuals with obesity undergoing bariatric surgery were included. Anthropometric, biochemical and quantitative computed tomography (QCT)-assessed body composition variables were collected at baseline and 1-year postoperatively for pre-post comparisons. Patients were divided into postoperative serum 25-hydroxyvitamin D [25(OH)D] deficient and normal groups for comparisons. Spearman correlation analysis was applied to explore correlations of postoperative 25(OH)D and its changes (△) with postoperative indicators. Linear regression analysis was applied to evaluate the predictive value of preoperative 25(OH)D for postoperative body composition. Results Postoperative 25(OH)D increased significantly (11.92 vs. 21.24 ng/mL, P < 0.001), but 72.6% of patients remained deficient. The deficient group had significantly higher erector spinae muscle fat (ESMF), ESMF fraction (ESMFF), psoas major muscle fat fraction (PMMFF), visceral adipose tissue (VAT) and VAT index (VATI) than the normal group ( P < 0.05). Postoperative 25(OH)D was negatively correlated with ESMF, ESMFF, PMMFF, VAT and VATI (false discovery rate-adjusted P < 0.05). No correlations between △25(OH)D and changes in body composition remained significant. Preoperative 25(OH)D does not predict postoperative body composition parameters ( P > 0.05). SG-only sensitivity analyses showed similar cross-sectional findings. Conclusions Vitamin D deficiency was prevalent postoperatively. Higher postoperative 25(OH)D was associated with lower muscle fat infiltration and visceral adiposity. Postoperative 25(OH)D and body composition monitoring are recommended to optimize long-term clinical outcomes.