Reading Boosts Cognitive Reserve to Protect Against Lead Exposure

BALTIMORE, July 30 -- Reading the written word may be mightier than lead poisoning, investigators here reported.

They found that avid reading, which stimulated cognitive reserve, helped fend off the cognition-draining effects of lead exposure in a group of smelter workers.

Workers who scored high on a test of reading ability showed no ill effects of lead exposure on cognitive function, Margit L. Bleecker, M.D., Ph.D., of the Center for Occupational and Environmental Neurology, and colleagues, reported in the July 31 issue of Neurology.

In contrast, workers with low scores on the reading test also had significantly lower scores on neuropsychological tests compared with the good readers, the investigators reported.

The two groups of smelter workers had identical blood levels of lead, which affected motor function similarly in the groups. Collectively, the data supported the view that reading promoted development of greater cognitive reserve, which protected the brain from lead exposure.

"Even though the two groups had similar lead exposure, the cognitive effects of lead were 2.5 times greater in workers with low reading ability," said Dr. Bleecker. "In contrast, the effect on motor speed was comparable in both groups, as cognitive reserve does not apply to motor speed."

"This suggests that high cognitive reserve has a protective effect that allowed these workers to maintain their functioning, even though lead affected their nervous system as shown by its effect on their motor skills," she added.

The theory of cognitive reserve is based on the premise that cognitive performance can be maintained in the presence of ongoing brain pathology, the authors noted. A variety of factors may contribute to cognitive reserve, including genetic, neuroanatomic, social, and environmental factors, one of which is reading achievement.

Dr. Bleecker and colleagues evaluated the effects of lead exposure on cognitive function in employees at a Canadian lead-smelting facility. Occupational lead exposure has been associated with impaired cognition, motor speed, and dexterity.

The workers were stratified by scores on the Wide Range Achievement Test-R (which reflects reading achievement) into groups with low and high cognitive reserve. The investigators then matched workers from each group into 56 pairs according to total lifetime weighted blood lead (TWA).

"A reading test identifies those self-educated individuals that left school early for a variety of sociocultural reasons and those individuals who graduated high school but are functionally illiterate," the authors stated.

Moreover, they added, measures of reading achievement better reflect cognitive reserve compared with other common surrogates, such as education and occupational attainment, which are more easily affected by opportunity.

The workers completed a battery of 14 neuropsychological tests that were chosen as outcome variables because of their reported associations with lead exposure. Employees with low cognitive reserve had worse scores on all 14 tests, and the differences achieved statistical significance for all but three of the tests (P=0.04 to P=0.00).

Further analysis revealed a dose-effect relationship between lead exposure and measures of cognitive function, motor speed, and dexterity in the workers with low cognitive reserve. In the group with high cognitive reserve, the only dose-effect relationships involved motor speed and dexterity, areas not expected to be influenced by cognitive reserve.

The results suggest that cognitive reserve modified the impact of lead exposure in workers with high cognitive reserve and allowed cognitive performance to be maintained, even though lead did affect the nervous system, as indicated by scores on motor performance, the authors concluded.