Aging is an Inevitable Risk Factor for Insulin Resistance

The present work looks into the different aspects of glucose homeostasis in the elderly patients in comparison to healthy younger subjects and patients with type 2 diabetes mellitus, relying on intravenous glucose tolerance test. A clinicobiochemical study was carried out comprising forty apparently healthy non-diabetic non-obese old individuals (mean age 65 +/- 4.8 years). Forty type 2 diabetic patients compared to thirty 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 constant decay (K-G), glucose and insulin area 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 control, had non-significantly different fasting plasma glucose in senile group but it was higher in diabetic patients, while fasting serum insulin was significantly higher in the studied groups than in healthy control group. The senile group showed significant reduction in glucose tolerance (K-G 1.36 +/- 0.3%/ min), decreased insulin sensitivity index (5.19 +/- 1.4 10(-4) min(-1) /[uU/ml]) and marked reduction of first phase insulin response (2.45 +/- 0.78 uIU/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 less than of type 2 diabetic patients. This study revealed that the insulin resistance seems to be characteristic feature of normal aging process and senility could be considered as an inevitable risk factor for glucose intolerance and metabolic syndrome with its accompanying health hazards. Insulin secretion, insulin clearance and interaction between insulin and target tissues are defective in elderly subjects. These functions are intermediate between healthy controls and type 2 diabetic patients and may predispose the elderly population to the risk of impaired glucose tolerance or diabetes mellitus with its attendant macrovascular and microvascular complications.