Renal function and long-term decline in cognitive function: the Baltimore Longitudinal Study of Aging.

BACKGROUND: Renal disease has been associated with greater risk of dementia and greater cognitive impairment. However, the relationship of lower renal function with long-term decline in specific domains of cognitive function remains unclear among community-dwelling, non-demented individuals.
METHODS: Stroke- and dementia-free participants (n = 2,116) were enrolled in the Baltimore Longitudinal Study of Aging, a community-based, prospective, longitudinal study. Renal function was estimated by the inverse of serum creatinine adjusted for age, sex and race and (in sensitivity analyses) estimated glomerular filtration rate (eGFR) using the MDRD formula. Outcome measures were changes in scores on 6 cognitive tests encompassing a range of cognitive functions, measured at 2-year intervals. Mixed-effects regression models examined the longitudinal relations of renal function with cognitive functions after adjusting for demographics, comorbidity and other potential confounders.
RESULTS: Mean age at initial testing was 53.9 years (SD 17.1), and 94 participants (4.4%) had an eGFR <60 ml/min/1.73 m(2) and 18.5% had at least one comorbidity. With increasing age, longitudinal increases in creatinine concentrations were associated with more rapid decline in performance on several cognitive measures, including the learning slope of the California Verbal Learning Test, a test of verbal learning (p < 0.01), and the Benton Visual Retention Test, a test of visual memory (p < 0.01). Associations were similar for changes in eGFRMDRD, which was also associated with the rate of decline in verbal memory.
CONCLUSION: In a community-based adult population, declines in renal function independently associated with greater long-term declines in visual memory and verbal memory and learning.