The higher the exposure to lead in everyday life, the lower were the scores on a variety of cognitive tests in elderly men. Researchers from the Harvard School of Public Health, Boston, Massachusetts examined the link between mental skills and life-time lead exposure among a subgroup of subjects in the Normative Aging Study, a cohort of community-dwelling elderly men. None of the men studied had dealt with high levels of lead in their work. Lead concentrations in blood and bone were measured from 1991 through 1999. Cognitive testing was performed from 1993 through 2001. It was found that a total of 1089 men, average age 69 years, had blood lead measurements and 761 of them also had bone lead measurements. All had completed at least one cognitive test and over two thirds had at least one repeat test approximately 3.5 years later. At the beginning of the study, the average blood lead concentration was 5 micrograms (µg) per decilitre. The average lead concentration in the kneecap, measured by an x-ray technique, was 20 µg per gram of bone mineral. The investigators found that there were substantial associations between different lead exposure markers and scores on cognitive tests. As blood lead levels increased, vocabulary scores went down. Above concentrations of 10 µg per dL, scores declined about 1 point for every µg/dL increase in lead level. However, this result did not persist when outliers were removed. As bone lead increased, the change in performance worsened over time on nearly all tests. The strongest effects were observed on performance and reaction time scores on visuospatial and visuomotor tests. For example, with increasing levels of patella lead levels (up to 60 µg per gram of bone), responses on the pattern-comparison test worsened over time. These results are based on a testing interval of only 3.5 years. It is possible that follow-up over longer periods of time might reveal stronger effects.
Epidemiology,
February 2007