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 RESULTS: Before surgery, 98.5% of patients had vitamin D insufficiency (25(OH)D <
30 μg/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.