DPP4 and type 1 diabetes mellitus: Some case studies conducted in patients with T1D documented potential protective effects on beta-cell function deriving from the use of cholecalciferol in addition to anti-inflammatory or anti-hyperglycemic agents, such as omega-3 polyunsaturated fatty acids (PUFA) or dipeptidyl peptidase-4 (DPP-4) inhibitors.