Differential Behavior of 25(OH)D and f25(OH)D3 in Patients with Morbid Obesity After Bariatric Surgery.

Background: Total 25-OH-vitamin D (25(OH)D) levels are decreased in patients with obesity, but few data exist regarding free-vitamin D3 (f25(OH)D3) concentrations. We aimed to evaluate the effect of bariatric surgery on 25(OH)D and f25(OH)D3 in a cohort of patients with morbid obesity.

Methods: Twenty-four patients submitted to sleeve gastrectomy (SG) (mean age 48 years, body mass index (BMI) 48.16±10.73k/m) were evaluated before and 1 year after surgery. Anthropometric data, parathormone (PTH), calcium, alkaline phosphatase, 25(OH)D, and f25(OH)D3 were recorded.

Results: 25(OH)D and f25(OH)D3 correlated well before and after SG. Baseline determinations did not correlate with BMI, but they inversely correlated with BMI 1 year after surgery (r=-0.46, p=0.02 and r=-0.60, p=0.002, respectively). Post-surgery % total body weight loss (%TBWL) was 27.4±13.8 %; f25(OH)D3 concentrations increased significantly (5.28±2.29 pg/mL vs 6.64±2.25 pg/mL; p=0.03), whereas 25(OH)D did not change. Patients who achieved a BMI <35 kg/m 1 year after surgery had significantly higher concentrations of f25(OH)D3 (7.9±1 pg/mL vs 4.8±1.1, p<0.001) and 25(OH)D (30.9±9.4 ng/mL vs 22.3±13.4; p=0.03) compared to those who remained with BMI >35 kg/m.

Conclusion: There is a significant inverse relationship between BMI and both f25(OH)D3 and 25(OH)D 1 year after surgery. Only f25(OH)D3 concentrations increased 1 year after surgery, which could be explained by a greater f25(OH)D3 sequestration before SG in the adipose tissue, potentially due to the more liposoluble nature of f25(OH)D3 than the protein-bound form 25(OH)D.