Endocrine Abstracts

Total vitamin D levels are decreased in obese patients probably due to an increased volume of distribution mechanism. Recently introduced direct assays allow the measurement of free-vitaminD3 levels (fvitD3). Few data are available regarding fvitD3 levels in obese people and the effect of bariatric surgery upon its circulating concentration. We aimed to evaluate fvitD3 in a cohort of obese patients before and after bariatric surgery treatment and its relationship to phosphocalcic parameters.

Methods: Retrospective study including 24 patients (48 y, 20 women, initial weight of 124.66±30.76 kg, waist 131.65±14.19 cm and BMI 48.16±10.73 kg/m²) treated with sleeve gastrectomy. All patients received standard supplementation with daily 800IU of colecalciferol p.o. after surgical procedure. Evaluation was done before and one year after the intervention and samples for measurement were collected during summertime period. Data regarding body weight, BMI, waist, lipid profile, albumin-corrected calcium, phosphate, PTH, 25-OH-vitaminD and fVitD3 was recorded before and after surgery.

Results: Before surgery, 25-OH-vitaminD in obese patients was 22.08±11.54 ng/ml and fvitD3 was 5.28±2.29 pg/ml; 25-OH-vitaminD and fvitD3 levels showed a positive correlation between them (r_s=0.7, P<0.0001). 25-OH-vitaminD showed an inverse correlation with PTH levels (r_s=−0.46, P<0.04) but there was no correlation with fvitD3. Neither 25-OH-vitaminD, nor fvitD3 correlated with weight or BMI before surgery. One year after bariatric surgery (waist 102.64±15.41 cm, BMI 34.82±9.0 kg/m²), mean 25-OH-vitaminD was 27.31±11.83 ng/ml (p=n.s vs pre-surgery) and fvitD3 increased to 6.64±2.25 pg/ml (P=0.03 vs pre-surgery). There was no statistical correlation between the percent change of fvitD3 and the magnitude of weight loss although absolute concentrations of fvitD3 and 25-OH-vitaminD were inversely correlated with final weight (r_s=−0.60, P=0.002 and r_s=−0.46, P=0.02 respectively).

Conclusion: fvitD3 is correlated with 25-OH-vitaminD either, pre and post bariatric surgery in morbidly obese patients and it increases 1 year after surgical procedure. Weight and both 25-OH-vitaminD and fvitD3, reestablished a negative correlation after surgery, being the last one of higher magnitude in coincidence with its increased circulating concentrations in the follow up period. This finding may be related with a postsurgical reduction of the kidnaping effect of adipose tissue and affects preferentially the free form rather the total vitD.