Impact of cognitive reserve on the relationship of lead exposure and neurobehavioral performance

Background: Cognitive reserve (CR)-a construct studied in many neurologic disorders-refers to the maintenance of cognitive performance in spite of ongoing underlying brain pathology. Objective: We hypothesized that a dose-effect relationship would exist between chronic occupational lead exposure and cognitive effects in workers with low CR but not in workers with high CR and identical lead exposure, and that level of CR would not influence the relationship between lead exposure and motor performance. Methods: We stratified currently employed lead smelter workers by Wide Range Achievement Test-R for reading (WRAT), a recognized measure of CR, into loCR and hiCR groups. From these two groups we matched 56 pairs on working lifetime weighted blood lead (TWA). We performed a factor analysis on 14 neuropsychological outcome variables. Within each CR group regression analyses after adjusting for age, alcohol use, and depression scale score tested for dose-effect relationships between TWA and outcome variables. Results: Both CR groups had comparable age, years employed, alcohol use, and current blood lead levels. Factor analysis provided three factors and five tests used in the regression analyses. Significant dose-effect relationships between TWA and cognitive tests present only in the IoCR group included Attention Factor and Digit Symbol. Both CR groups demonstrated significant dose-effect relationships on the Motor Factor. Conclusion: This study found that cognitive reserve protects against the effect of chronic lead exposure on select measures of cognitive performance but not on motor performance.