Effect of aging on glucose homeostasis: accelerated deterioration of beta-cell function in individuals with impaired glucose tolerance.
OBJECTIVE
To examine the effect of aging on insulin secretion (first- and second-phase insulin release) and insulin sensitivity in people with normal glucose tolerance (NGT) or impaired glucose tolerance (IGT).


METHODS
First- and second-phase insulin secretion and insulin sensitivity were assessed in hyperglycemic clamp experiments in 266 individuals with NGT and 130 individuals with IGT, ranging in age from approximately 20 to approximately 70 years. Changes in beta-cell function were compared using the disposition index to adjust for differences in insulin sensitivity.


RESULTS
As expected, both phases of insulin release and insulin sensitivity were reduced in individuals with IGT (all P < 0.01). Insulin sensitivity was not independently correlated with age in either group. In people with NGT, the disposition index for first- and second-phase insulin release decreased similarly at a rate of approximately 0.7% per year. In people with IGT, the disposition indexes for first- and second-phase insulin release decreased at greater rates ( approximately 2.2 and 1.4% per year, P = 0.002 and 0.009, respectively, vs. NGT), with the decrease in first phase being greater than that of second phase (P = 0.025).


CONCLUSIONS
Insulin secretion (both first and second phase) normally decreases at a rate of approximately 0.7% per year with aging; this decrease in beta-cell function is accelerated about two-fold in people with impaired glucose tolerance-first phase to a greater extent than second phase. Finally, aging per se has no effect on insulin sensitivity independent of changes in body composition.
Szoke
Ervin
E
Department of Medicine, University of Rochester School of Medicine, Rochester, New York, USA.
Shrayyef
Muhammad Z
MZ
Messing
Susan
S
Woerle
Hans J
HJ
van Haeften
Timon W
TW
Meyer
Christian
C
Mitrakou
Asimina
A
Pimenta
Walkyria
W
Gerich
John E
JE
D000328:Adult; D000368:Aged; D000375:Aging; D001786:Blood Glucose / Q000378:metabolism*; D015992:Body Mass Index; D005260:Female; D018149:Glucose Intolerance / Q000097:blood* / Q000378:metabolism / Q000503:physiopathology; D006706:Homeostasis / Q000502:physiology; D006801:Humans; D007328:Insulin / Q000097:blood; D050417:Insulin-Secreting Cells / Q000378:metabolism* / Q000473:pathology; D008297:Male; D008875:Middle Aged
D001786:Blood Glucose; D007328:Insulin