Cumulative exposure to lead and cognition in persons with Parkinson's disease

Dementia is an important consequence of Parkinson's disease (PD), with few known modifiable risk factors. Cumulative exposure to lead, at levels experienced in the community, may exacerbate PD-related neural dysfunction, resulting in impaired cognition. Among 101 persons with PD ("cases") and, separately, 50 persons without PD ("controls"), we evaluated cumulative lead exposure, gauged by tibia and patella bone lead concentrations, in relation to cognitive function, assessed using a telephone battery developed and validated in a separate sample of PD patients. We also assessed the interaction between lead and case-control status. After multivariable adjustment, higher tibia bone lead concentration among PD cases was associated with worse performance on all of the individual telephone tests. In particular, tibia lead levels corresponded to significantly worse performance on a telephone analog of the Mini-Mental State Examination and tests of working memory and attention. Moreover, higher tibia bone lead concentration was associated with significantly worse global composite score encompassing all the cognitive tests (P = 0.04). The magnitude of association per standard deviation increment in tibia bone lead level was equivalent to the difference in global scores among controls in our study, who were approximately 7 years apart in age. The tibia lead-cognition association was notably stronger within cases than within controls (P_difference = 0.06). Patella bone lead concentration was not consistently associated with performance on the tests. These data provide evidence suggesting that cumulative exposure to lead may result in worsened cognition among persons with PD.