Age-related increase in haemoglobin A1c and fasting plasma glucose is accompanied by a decrease in β cell function without change in insulin sensitivity:: evidence from a cross-sectional study of hospital personnel

Aims To examine the influence of age on glucose homeostasis in a population of healthy, non-diabetic hospital personnel. Methods One hundred and twenty female and 71 male non-diabetic individuals (fasting plasma glucose < 7.0 mmol/l) were fasted overnight prior to blood sampling. Glycated haemoglobin (HbA(1c)), fasting plasma glucose (FPG) and fasting plasma insulin (FPI) were measured using a BioRad Diamat automated HPLC, a Hitachi 747 analyser and a sensitive in-house radioimmunoassay, respectively. Mathematical modelling of the fasting glucose and insulin pairs (homeostasis model assessment (HOMA)) generated indices of pancreatic beta cell function, HOMA-B and tissue insulin sensitivity HOMA-S. Results Spearman rank correlation analysis showed that in the whole group there was a significant negative correlation between age and HOMA-B (r(s) = -0.218, P = 0.0022) and a significant positive correlation between age and both HbA(1c) (r(s) = 0.307, P = 0.0001) and FPG (r(s) = 0.26, P = 0.0003). There was no correlation between age and either FPI (r(s) = -0.08, P = 0.266) or HOMA-S (r(s) = 0.024, P = 0.75). Analysis by gender showed the above associations to be present in the females (r(s) = -0.243, P = 0.0076; r(s) = 0.304, P = 0.0007; r(s) = 0.32, P = 0.0004 for age vs. HOMA-B, HbA(1c), and FPG, respectively). Again there was no correlation of age with FPI or insulin sensitivity. In the males there was a significant correlation of HbA(1c) with age (r(s) = 0.35, P = 0.002), but no significant correlation of age with any of the other parameters. Conclusions Glycaemic control deteriorates with age in healthy, non-diabetic individuals. Age-related rises in FPG and haemoglobin A(1c) result from a small but steady decline in pancreatic beta cell function.