Diabetes mellitus type 2 (T2DM) is a worldwide pandemic disease. T2DM and hypertension (HT) are closely related and classified as non-communicable diseases. These conditions represent as part of metabolic syndrome. Ageing is an independent risk factor of both diseases. Accumulation of reactive oxygen species (ROS) or imbalance of ROS and antioxidant system, which cause endothelial dysfunction (ED) through depletion of nitric oxide (NO), is likely to be the main risk factor in ageing, T2DM and HT. The organ that is rich in capillary blood supply like the islets of Langerhans and renal glomeruli, is theoretically prone to ED after long exposure to accumulation of various oxidants derived from dietary products, such as superoxide radical (O2-), hydroxyl radical (OH), malondialdehyde (MDA) and peroxynitrite (ONOO-), a potent long lived oxidant and cytotoxic. Preventive measures to correct imbalance of oxidant and antioxidation pathways and the sequential effects should be implemented since birth or childhood period by ways of proper diet, exercise, adequate supply of natural antioxidants and lifestyle modifications.