Deterioration of glucose tolerance in non-diabetic non-IGT elderly population: potential role of Beta cell dysfunction and insulin insensitivity

Aim: As the human community develops, the group of aged individuals constitutes a larger percent of the total population. This particular group of people is characterized by increased incidence of macrovascular complications that are similar to those described in the metabolic syndrome or type 2 diabetes. Moreover, it is well known that the incidence as well as the prevalence of type 2 diabetes and impaired glucose tolerance is more common in old age people. The mechanism of age-related glucose intolerance is not yet completely clear. Subjects and A clinicobiochemical study was carried out comprising 20 apparently healthy non-diabetic nonobese old individuals [mean age 65 +/- 4.8 years] and 20 type 2 diabetic patients compared to 10 healthy young subjects. The senile group had no family history of diabetes. Cases with renal, hepatic, gastrointestinal, or endocrine abnormalities were excluded from the study. Intravenous glucose tolerance test [ivGTT] was done with sampling at 0, 5, 10, 15, 30, 45, and 60 min after glucose load and the following estimations were undertaken: glucose decay constant [kG], glucose and insulin areas under the curve, insulnogenic index, first phase insulin response, insulin resistance index and fractional insulin clearance. The senile and diabetic groups, when compared to the controls, had a ronsignificantly different fasting plasma glucose, but it was higher in diabetic patients. Fasting serum insulin was significantly higher in the studied groups than in the healthy control group. The senile group showed a significant reduction in glucose tolerance [KG 1.36 +/- 0.3%/min], decreased insulin sensitivity index [5.19 +/- 1.4 10-4 min-1 /[micro U/ml] and a marked reduction of first phase insulin response [2.45 +/- 0.78 micro U/ml per mg/dl], when compared with the control group. However, the degree of glucose intolerance and insulin insensitivity of the senile group was still significantly lower than that of type 2 diabetic patients. This study revealed that the insulin resistance seems to be a characteristic feature of the normal aging process and senility could be considered as an inevitable risk factor for glucose intolerance and metabolic syndrome with its accompanying health hazards. Conclusions: Insulin secretion, insulin clearance and interaction between insulin and target tissues are defective in elderly subjects. These functions are intermediate between healthy controls and NIDDM patients and may predispose the elderly population to the risk of impaired glucose tolerance or diabetes mellitus with its attendant macrovascular and microvascular complications