The decline in glomerular filtration rate (GFR) associated with aging is one of the most important predisposing causes of kidney failure in old age. Identifying persons at risk for accelerated GFR decline is an essential first step in the development of preventive measures to preserve kidney function in the elderly. Heart rate (HR) has not yet been studied as a risk factor for GFR decline in the general population. In the RENIS-T6 (Renal Iohexol-Clearance Survey in Tromsø 6), we measured baseline ambulatory HR and GFR as iohexol clearance in a representative, middle-aged cohort of 1627 persons without self-reported diabetes mellitus, cardiovascular disease, or kidney disease. In the RENIS-FU (RENIS Follow-Up Study), we repeated the GFR measurements and calculated the rate of GFR decline in 81% of the participants after a median follow-up of 5.6 years. The unadjusted mean rate of GFR decline was 0.96 mL/min per year. In multivariable-adjusted linear mixed models, 10 bpm higher ambulatory 24-hour and daytime HRs and office HR were associated with steeper GFR decline rates of 0.20 to 0.21 mL/min per year ( P ≤0.01). The odds ratio for predicting a rate of GFR decline twice that of the population mean in a fully adjusted model was 1.24 ( P =0.01) for ambulatory 24-hour HR. Office HR was also an independent predictor of a steeper rate of GFR decline. HR may be a useful biomarker to identify persons at risk of accelerated GFR decline.
Background Although the relationship between manifest chronic kidney disease and reduced cognitive function is well established, limited data exists on GFR and cognitive function in the general population. Both the brain and kidneys have low-impedance vascular beds, rendering them susceptible to damage from pulsatile blood flow. An association between mildly reduced GFR and cognitive function in the healthy general population may reveal early disease mechanisms underlying low-grade impairment of both organs as well as the possibility for intervention. Our aim was to identify an early stage of low-grade impairments in both the brain and the kidneys in the general population. Methods This investigation was a population-based cross-sectional study that included 1627 participants aged 50–62 years who were representative of the general population in the municipality of Tromsø, Norway. The associations between GFR, measured as iohexol clearance, the urinary albumin-creatinine ratio and performance on five tests of cognitive function—the Digit Symbol Substitution Test, the finger tapping test, the Mini-Mental State Examination and the 12-word test parts 1 and 2 – were examined. The data were adjusted for factors known to be associated with both GFR and cognitive function, including cardiovascular risk factors, medications and education level. Results In multivariate adjusted linear regression analyses, we did not observe associations of the measured GFR or albumin-creatinine ratio with performance on any of the five cognitive tests. In an analysis without adjustment for the education level, an association of worse performance on the Digit Symbol Substitution Test with higher measured GFR ( p = 0.03) was observed. An exploratory analysis revealed an inverse relationship between mGFR and a higher education level that remained significant after adjusting for factors known to influence mGFR. Conclusions We did not find evidence of an association between low-grade impairments in either the kidneys or the brain in the middle-aged general population. A possible association between a high GFR and reduced cognitive function should be investigated in future studies. Electronic supplementary material The online version of this article (10.1186/s12882-019-1356-4) contains supplementary material, which is available to authorized users.
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