Childhood cardiorespiratory fitness and the early markers of kidney disease in middle age: A population-based cohort study

ObjectivesTo investigate the relationship of childhood cardiorespiratory fitness with early markers of chronic kidney disease, glomerular hyperfiltration and albuminuria, in midlife.DesignProspective cohort study.MethodsThis study included 1371 participants aged 36–49 years who participated in the 1985 Australian Schools Health and Fitness Survey when they were 7–15 years of age. Childhood cardiorespiratory fitness was estimated by the time taken to complete a 1.6- km run. Blood and urine samples were collected at follow-up. Log-binomial regression was used to determine the associations of childhood cardiorespiratory fitness with glomerular hyperfiltration [estimated glomerular filtration rate (mL/min/1.73 m²) > 95th percentile standardized for age and sex] and albuminuria (urine albumin-to-creatinine ratio ≥ 2.5 mg/mmol in males or ≥3.5 mg/mmol in females) in midlife.ResultsCompared with women with high childhood cardiorespiratory fitness, those with lower childhood cardiorespiratory fitness had a higher risk of glomerular hyperfiltration in midlife after adjusting for childhood age, the duration of follow-up, and midlife smoking status [adjusted relative risk = 2.86, 95% confidence interval, 1.04–7.86 for individuals with moderate childhood cardiorespiratory fitness (P = 0.04), and adjusted relative risk = 3.38, 95% confidence interval, 1.13–10.14 for individuals with low childhood cardiorespiratory fitness (P = 0.03)]. Further adjustment for childhood and midlife body mass index resulted in a slightly attenuated and statistically non-significant association. No significant associations were found with glomerular hyperfiltration in males or albuminuria in either males or females.ConclusionsLow cardiorespiratory fitness in childhood may increase the risk of glomerular hyperfiltration in midlife in females, possibly via a path through adult cardiorespiratory fitness.