Trummer C, et al. - In this trial that consisted of healthy premenopausal women, researchers ascertained if vitamin D supplementation has any substantial impact on metabolic and endocrine parameters. This trial was conducted between March 2013 and October 2017 at the Medical University of Graz, Austria. For this investigation, 150 healthy premenopausal women with 25-hydroxyvitamin D (25[OH]D) levels < 75 nmol/L once weekly received either 20,000 IU of cholecalciferol or placebo (2:1 ratio) over 24 weeks. Approximately 85% of participants completed the study. The plasma glucose area under the curve (AUCgluc) was the primary outcome measure. A significant treatment effect of vitamin D supplementation on homeostatic model assessment-insulin resistance and quantitative insulin-sensitivity check index (QUICKI) was evident. On the other hand, no significant treatment effect on AUCgluc was observed.