Hyperglycaemia and its relation to cardiovascular morbidity and mortality: has it been resolved?
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Type 2 diabetes is preceded by long-standing asymptomatic hyperglycaemia. This prediabetic state is characterised by elevated post-prandial hyperglycaemia and yet normal fasting plasma glucose (FPG). The relationship between abnormal circulating glucose levels and the development of long-term diabetic complications became apparent 70 years ago, soon after the introduction of insulin and the prevention of early death due to ketoacidosis. The main issues regarding diabetes and the various target organs throughout the cardiovascular system, including coronary artery disease (CAD), peripheral vascular disease (PVD), increased intima-media thickness (IMT) and stroke, are as follows: CAD causes much of the serious morbidity and mortality in patients with diabetes, who have a 2- to 4-fold increased risk of CAD; epidemiological evidence confirms an association between diabetes and increased prevalence of PVD; and diabetes induces increased IMT and stroke by adversely affecting cerebrovascular circulation including the carotid artery, akin to its effects in the coronary and lower extremity vasculature. In diabetes, FPG and HbA1C are the main parameters of glucose metabolism used to monitor and control hyperglycaemia. Recently, particular emphasis has been placed on post-prandial plasma glucose as a parameter in the metabolic assessment of diabetic patients. Therefore, while addressing the question of hyperglycaemia and its relation to cardiovascular morbidity and mortality, we have to look for the possible mechanisms by which diabetic hyperglycaemia causes these complications. Then, we must examine the evidence on how the main parameters of glucose metabolism correlate with cardiovascular complications. This review addresses these issues.