['The worldwide increase in end-stage renal disease has been alleged to be associated with insulin resistance-related conditions. Insulin resistance and the concomitant compensatory hyperinsulinaemia may accelerate age-related decline in renal function through inducing glomerular hyperfiltration, even in non-diabetic subjects. This population-based study is the first to investigate whether fasting insulin concentrations modify the relationship between age and renal function in a general non-diabetic population.', 'Fasting insulin was measured in 3432 subjects, representing the general population. Cross-sectional analyses of the association between age, renal function and its modification by insulin were performed by means of linear regression. Renal function was assessed as 24-h creatinine clearance (CrCl) and 24-h urinary albumine excretion (UAE).', 'Age was 48 +/- 12 (range: 28-75) years, 44% were male, CrCl was 100 +/- 26 ml/min and UAE was 7.0 (5.4-10.7)] mg/24 h. The results confirmed a parabolic relation between age and renal function. Fasting insulin modified these parabolic relationships of age with CrCl and UAE (P < 0.001 for both interaction terms), in such a way that hyperinsulinaemia is associated with a stronger inverse parabolic relation between age and CrCl, and stronger positive parabolic relation between age and UAE at an older age than lower insulin concentrations.'] Does fasting insulin modify the relation between age and renal function?