Type 2 Diabetes is closely associated with our daily diets and has become a global health problem with an increasing number of patients. Recent observational and randomized studies on vitamin D-3 suggested that higher plasma 25-hydroxyvitamin D-3 [25(OH)D-3] concentrations and more vitamin D-3 intake are associated with lower risk of type 2 diabetes, which is characterized by postprandial hyperglycemia due to inappropriate glucose stimulated insulin secretion (GSIS) and its age-dependent increase of onset. However, rapid action of dietary vitamin D-3 on the postprandial glucose profile has not been analyzed. When vitamin D-3 is orally ingested in mice aged 12-14 weeks during an oral glucose tolerance test (OGTT), the serum glucose profile was not changed. In contrast, when OGTT was performed with old mice aged 30-34 weeks, the glucose profile was dramatically improved with increased insulin secretion, suggesting that orally ingested vitamin D-3 potentiated GSIS in aged mice. Interestingly, there was also a significant increase in plasma GLP-1 in these aged mice. Our results suggest that orally ingested dietary vitamin D-3 in aged mice improves glucose metabolism as a GLP-1 enhancer. (C) 2015 Elsevier Inc. All rights reserved.