Authors: R. A. Shih, PhD, T. A. Glass, PhD, K. Bandeen-Roche, PhD, M. C. Carlson, PhD, K. I. Bolla, PhD, A. C. Todd, PhD and B. S. Schwartz, MD, MS

Source: NEUROLOGY 2006;67:1556-1562

Objective:  To determine if long-term exposure to high levels of lead in the environment is associated with decrements in cognitive ability in older Americans.

Methods: We completed a cross-sectional analysis using multiple linear regression to evaluate associations of recent (in blood) and cumulative (in tibia) lead dose with cognitive function in 991 sociodemographically diverse, community-dwelling adults, aged 50 to 70 years, randomly selected from 65 contiguous neighborhoods in Baltimore, MD. Tibia lead was measured with 109Cd induced K-shell X-ray fluorescence. Seven summary measures of cognitive function were created based on standard tests in these domains: language, processing speed, eye-hand coordination, executive functioning, verbal memory and learning, visual memory, and visuoconstruction.

Results: The mean (SD) blood lead level was 3.5 (2.2) µg/dL and tibia lead level was 18.7 (11.2) µg/g. Higher tibia lead levels were consistently associated with worse cognitive function in all seven domains after adjusting for age, sex, APOE-{varepsilon}4, and testing technician (six domains p ≤ 0.01, one domain p ≤ 0.05). Blood lead was not associated with any cognitive domain. Associations with tibia lead were attenuated after adjustment for years of education, wealth, and race/ethnicity.

Conclusions: Independent of recent lead dose, retained cumulative dose resulting from previous environmental exposures may have persistent effects on cognitive function. A portion of age-related decrements in cognitive function in this population may be associated with earlier lead exposure.