Relationship between glucose tolerance and glucose-stimulated insulin response in 65-year-olds.

BACKGROUND Decreased insulin secretion may contribute to the deterioration of glucose tolerance associated with aging. METHODS We studied the insulin response to a 3-hour hyperglycemic clamp (10 mM) of 19 young (24 +/- 1 y) subjects with normal glucose tolerance and 60 older (65 +/- 1 y) subjects with various levels of glucose tolerance. RESULTS The noninsulin dependent diabetic (NIDDM) group had a diminished first phase immunoreactive (IR)-insulin response compared to young and nondiabetic older groups (p < .05). The older groups had a lower rate of change in IR insulin concentration during the third hour of hyperglycemia compared to the young group (p < .05). This was not, however, a universal finding, because a decreased third hour response was not seen in a subgroup of older subjects whose glucose tolerance was similar to that of the young group. Another subgroup of older subjects with a decrease in glucose tolerance mild enough to be considered normal by the National Diabetes Group Criteria tended to have both an increase in the early insulin response and a decrease in the third hour response. More severe decreases in glucose tolerance were associated with blunting of the early response. CONCLUSION Aberrations in early and late phase glucose-stimulated insulin responses appear to be present in older subjects with even mildly decreased glucose tolerance. Some individuals, however, show no evidence of deterioration of glucose tolerance or insulin response to glucose with aging, at least up to age 70 years.