Effects of Vitamin D Supplefmentation on Outcome of Low-Calorie Diet in Workers Presenting Obesity or Overweight: A Retrospective Observational Study

Aim: Growing evidence underscores the inverse association between serum vitamin D (vit D) and chronic conditions such as metabolic syndrome, diabetes and obesity. The aim of this retrospective study was to compare weight loss and metabolic serum biomarkers in subjects on low-calorie diet receiving vit D supplementation versus those not receiving it. Methods: The study considered 405 indoor sedentary workers with overweight/obesity and vit D insufficiency, who participated to a health fitness program between 2011-2013. Participants were recommended a moderately-low calorie diet plus vit D supplementation with 150,000 or 900,000 IU cumulative over 6 months in case of hypovitaminosis D (according to the guidelines at the enrollment), while those with optimal levels were recommended only diet. Participants were evaluated at baseline (T0), and after 6 months (T1). Anthropometric parameters, BMI, waist circumference (WC), serum 25-hydroxyvitamin D concentration ([25(OH)D]) and glycated hemoglobin (HbA1c) were assessed at T0 and T1. Results: Participants fell into one of three groups: (A) not supplemented, (B) receiving 150,000 IU and (C) receiving 900,000 IU cumulative over 6 months. Overall, the supplementation was associated with increased [25(OH)D], but only the dosage of group C was associated with the achievement of optimal vit D status. A significantly greater weight decrease was observed in group B (-4.1 kg) and C (-4.5 kg) compared to untreated (-1.2 kg). WC reduction was higher in the vit D groups (group B: −3.95 cm; group C; −6.20 cm; untreated: −3.21 cm; p < 0.05). When setting the threshold for obesity at BMI > 30kg/m2, [25(OH)D] no longer correlated with body fat or weight. [25(OH)D] inversely correlated with the Homeostatic Model Assessment for Insulin Resistance and remained significant after adjustment for BMI. Conclusions: Higher [25(OH)D] levels were associated to a greater weight loss and enhanced the beneficial effects of a reduced-calorie diet in individuals with BMI > 30 kg/m2.