Hyperinsulinemia--how innocent a bystander?

Hyperinsulinemia is very much in the spotlight. Debate rages as to its significance and role in the etiology not only of NIDDM, but also other morphological and metabolic risk factors for atherosclerotic cardiovascular disease, including upper-body obesity, dyslipidemia, hypertension, and hyperuricemia. Epidemiological data support a key role for hyperinsulinemia in these disorders but it is far from conclusive except for the fact that hyperinsulinemia and insulin resistance may be present many years before the onset of impaired glucose tolerance and NIDDM, and clearly play a role in their etiology. The thrifty genotype hypothesis provides a plausible basis for a better understanding of how hyperinsulinemia and insulin resistance could lead to glucose intolerance and atherosclerotic cardiovascular disease, but the detailed biochemical mechanisms remain elusive. A role for increased sympathetic nervous system activity, resulting from hypothalamic stimulation as a primary event causing hyperinsulinemia, cannot be excluded as a cause of hyperinsulinemia. The current focus on hyperinsulinemia also has resulted in closer examination of the therapy of diabetes and hypertension, emphasizing the need to avoid hyperinsulinemia in both IDDM and NIDDM individuals because of the putative risk of atherosclerotic cardiovascular disease and hypertension. There is still a paucity of epidemiological data to support a role for hyperinsulinemia in the etiology of hypertension. However, clinical practice already is being influenced by the fact that ACE inhibitors have been shown to reduce insulin resistance in clinical research studies. The research reviewed here, particularly that relating to hyperinsulinemia, insulin resistance, and cardiovascular disease risk factors, has opened new vistas for the treatment and prevention of NIDDM and atherosclerotic cardiovascular disease. Appropriate exercise clearly is associated with improved insulin sensitivity, modification of CVD risk factors, and lower prevalence of NIDDM. Upper-body obesity, the latest culprit in the field, can also be reduced by exercise. Hyperinsulinemia and insulin resistance can be detected in children, adolescents, and young adults. NIDDM can be prevented, but clearly, intervention needs to commence in childhood, and intensive risk factor intervention in subjects with NIDDM can reduce the risk of atherosclerotic cardiovascular disease. It seems paradoxical that prevention of NIDDM and atherosclerotic cardiovascular disease are now possible even though the biochemical and molecular basis of these disorders is not fully understood.