Core Idea

With a rapidly aging population, it’s no surprise that severe dementia is a topic of great concern.  Nevertheless, as these authors point out, milder forms of cognitive impairment are more common and are very detrimental.  Furthermore, these milder forms of cognitive impairment may be more susceptible to prevention and treatment.  For instance, a great deal of research has focused on lead exposure as a potential modifiable risk factor, in which a link was found between lead and declined cognitive function in children as well as adults who are exposed to it in work settings.  Limited research however, has looked at this association – lead exposure and cognitive impairment – with an adult population in a non-occupational setting and for changes in cognitive performance over time. Doing so was the goal of this study.

What they say

The researchers used a sub-group of the VA Normative Aging Study.  These participants were healthy men from the general population in the Greater Boston area.  From 1991-1999 measures of their bone lead were collected, and from 1993 through 2001 their scores on a series of cognitive tests were measured, with blood lead levels taken at each time they took the series of tests.  These measurements were then analyzed using complex statistical methods.

Although the researchers found some nonlinear associations between test scores and blood and bone lead with a cross-sectional analysis of the data, the more significant and stronger finding was the inverse relationship between bone lead and cognitive test performance for almost all cognitive tests over time; that is, the researches found that the more bone lead there was, the lower the cognitive performance.  This finding was especially strong for visuospatial and visuomotor tests.

What it means

Although there have been numerous studies of the association between lead exposure and cognitive performance, most were done on participants in occupational settings, they did not take into great consideration the different effects on each cognitive domain, they only used lead in the blood as a biomarker, and they mainly looked at the relationship with a cross sectional analysis, rather than in change over time (a longitudinal analysis).  However, when looking at this relationship among older men in a non-working setting, using both lead in the blood and lead in the bone as biomarkers, measuring performance on a number of cognitive tests, and taking these measurements over time, the researchers found an inverse relationship between bone lead and cognitive test performance for almost all cognitive tests. They conclude that lead exposure, even in a setting and population that’s exposed to it in a lesser degree, may lead to a decline in cognitive function, and may be especially a threat to the visuospatial/visuomotor domain. 

The authors noted several limitations of this study.  They are 1) although they tried to control for factors that could affect lead concentrations and cognitive performance, e.g. age and education, test performance could be derived by a multitude of factors, thus the results could be biased by the extent the researchers did not control for these factors, 2) in repeated-measures analyses a number of the subjects did not take all the tests twice, and 3) their results for change in cognitive test scores over time are based on an average of only 3.5 years between tests, and it is possible that follow-up over longer periods of time would lead to other effects.  They recommend that further research should be taken on the relationship between lead and cognitive performance, as lead could be a potential modifiable risk factor in terms of cognitive impairment.

Reference

Weisskopf, M., Proctor, S., Wright, R., et al.  (2007).  Cumulative Lead Exposure and Cognitive Performance Among Elderly Men.  Epidemiology, 18(1), 59-66.