Cumulative exposure to lead in relation to cognitive function in older women

Abstract

Background: Recent data indicate that chronic low-level exposure to lead is associated with accelerated declines in cognition in older age, but this has not been examined in women.

Objective: We examined biomarkers of lead exposure in relation to performance on a battery of cognitive tests among older women.

Methods: Patella and tibia bone lead--measures of cumulative exposure over many years--and blood lead, a measure of recent exposure, were assessed in 587 women 47-74 years of age. We assessed their cognitive function 5 years later using validated telephone interviews.

Results: Mean +/- SD lead levels in tibia, patella, and blood were 10.5 +/- 9.7 microg/g bone, 12.6 +/- 11.6 microg/g bone, and 2.9 +/- 1.9 microg/dL, respectively, consistent with community-level exposures. In multivariable-adjusted analyses of all cognitive tests combined, levels of all three lead biomarkers were associated with worse cognitive performance. The association between bone lead and letter fluency score differed dramatically from the other bone lead-cognitive score associations, and exclusion of this particular score from the combined analyses strengthened the associations between bone lead and cognitive performance. Results were statistically significant only for tibia lead: one SD increase in tibia lead corresponded to a 0.051-unit lower standardized summary cognitive score (95% confidence interval: -0.099 to -0.003; p = 0.04), similar to the difference in cognitive scores we observed between women who were 3 years apart in age.

Conclusions: These findings suggest that cumulative exposure to lead, even at low levels experienced in community settings, may have adverse consequences for women's cognition in older age.

Keywords: KXRF bone lead; aging; blood lead; cognitive function; epidemiology; women.

Figure 1

Adjusted mean difference (95% CI) in specific standardized cognitive test scores per SD increment in lead biomarker. Values are adjusted for age and age-squared at lead assessment, age at cognitive assessment, education, husband’s education, alcohol consumption, smoking status, physical activity, aspirin use, ibuprofen use, use of vitamin E supplements, menopausal status and postmenopausal hormone use, lead substudy source, and cognitive substudy source. Numbers left of bars indicate p-values. aAverage of zscores from the immediate and delayed recall of both the EBMT and the TICS 10-word list.