Cross-Sectional and Longitudinal Relationships Between Cerebrospinal Fluid Biomarkers and Cognitive Function in People Without Cognitive Impairment From Across the Adult Life Span

IMPORTANCE Age-related cognitive decline among older individuals with normal cognition is a complex trait that potentially derives from processes of aging, inherited vulnerabilities, environmental factors, and common latent diseases that can progress to cause dementia, such as Alzheimer disease and vascular brain injury. OBJECTIVE To use cerebrospinal fluid (CSF) biomarkers to gain insight into this complex trait. DESIGN, SETTING, AND PARTICIPANTS Secondary analyses of an academic multicenter cross-sectional (n = 315) and longitudinal (n = 158) study of 5 neuropsychological tests (Immediate Recall, Delayed Recall, Trail Making Test Parts A and B, and Category Fluency) in cognitively normal individuals aged 21 to 100 years. MAIN OUTCOMES AND MEASURES To investigate the association of these cognitive function test results with age, sex, educational level, inheritance of the epsilon 4 allele of the apolipoprotein E gene, and CSF concentrations of beta-amyloid 42 (A beta 42) and tau (biomarkers of Alzheimer disease) as well as F-2-isoprostanes (measures of free radical injury). RESULTS Age and educational level were broadly predictive of cross-sectional cognitive performance; of the genetic and CSF measures, only greater CSF F-2-isoprostane concentration was significantly associated with poorer executive function (adjusted R-2 <= 0.31). Longitudinal measures of cognitive abilities, except Category Fluency, also were associated broadly with age; of the genetic and CSF measures, only lower baseline CSF A beta 42 concentration was associated with longitudinal measures of immediate and delayed recall (marginal R-2 <= 0.31). CONCLUSIONS AND RELEVANCE Our results suggest that age and educational level accounted for a substantial minority of variance in cross-sectional or longitudinal cognitive test performance in this large group of cognitively normal adults. Latent Alzheimer disease and other diseases that produce free radical injury, such as vascular brain injury, accounted for a small amount of variation in cognitive test performance across the adult human life span. Additional genetic and environmental factors likely contribute substantially to age-related cognitive decline.