Oral High-Dose Vitamin D Dissolved in Oil Raised Serum 25-Hydroxy-Vitamin D to Physiological Levels in Obese Patients After Sleeve Gastrectomy-A Double-Blind, Randomized, and Placebo-Controlled Trial. - Wolf E; Utech M; Stehle P; Büsing M; Helfrich HP; Stoffel-Wagner B; Egert S; Alteheld B; Riege R; Knapp A; Ellinger S (Obesity surgery, 2016)