Vitamin D in adipose tissue and serum 25-hydroxyvitamin D after roux-en-Y gastric bypass

Vitamin D is stored in body fat. The purpose of this study was to determine vitamin D concentration in abdominal fat of obese patients who underwent roux‐en‐Y gastric bypass (RYGB), and to describe changes in serum 25‐hydroxyvitamin D (25(OH)D) levels in relation to loss of body fat. Subjects from a single clinic who were scheduled for RYGB were invited into the study. Abdominal subcutaneous, omental, and mesenteric fat were obtained at time of surgery. Adipose vitamin D₂ and vitamin D₃ concentrations were measured by high‐performance liquid chromatography (HPLC). Weight and serum 25(OH)D were assessed at baseline and every 3 months up to 1 year. Seventeen subjects were included, and fat samples were available from eleven. Total vitamin D content in subcutaneous abdominal fat was 297.2 ± 727.7 ng/g tissue, and a wide range was observed (4–2,470 ng/g). Both vitamin D₂ and vitamin D₃ were detected in some of the fat samples. At baseline, 25(OH)D was 23.1 ± 12.6 ng/ml. Average weight loss was 54.8 kg at 12 months, of which ～40 kg was fat mass. Despite daily vitamin D intake of ≥2,500 IU throughout the study, no significant increase in serum 25(OH)D was observed, with mean serum concentration of 25(OH)D at 1 year of 26.2 ± 5.36 ng/ml (P = 0.58). We conclude that vitamin D in adipose tissue does not significantly contribute to serum 25(OH)D despite dramatic loss of fat mass after RYGB.