Dementia is a major health concern in individuals with Parkinson’s disease, but why some Parkinson’s patients develop dementia and some don’t is not understood. Emerging evidence suggests that exposure to toxicants, such as lead, may affect the risk of neurodegenerative conditions, like Parkinson’s disease and of poor cognitive function in adulthood, possibly by some of the same mechanisms.
A team of investigators from Harvard, Rush University and the University of Michigan, led by the Harvard-NIEHS Center’s Metals Research Core leader, Marc Weisskopf, investigated the effects of lead exposure in Parkinson’s disease patients with varying degrees of cognitive dysfunction.
They recruited 101 Parkinson’s Disease (PD) patients and 50 controls from an ongoing project at the Brigham & Women’s Hospital and the Beth Israel Deaconess Medical Center in Boston. Cumulative exposure to lead was assessed with a noninvasive imaging technique that measures lead content in bone, where it accumulates over the lifetime. To assess participants’ cognition, the researchers developed a novel telephone-based battery of tests aimed at evaluating mental abilities that typically decline in PD.
The tests were designed to be administered over the phone, which offers some practical advantages over in-person methods, notably enhanced participation. This advantage is especially important for studies involving participants who have mobility difficulties, such as those with PD.
“We found that higher cumulative exposure to lead, gauged by tibia bone lead concentration, is associated with worse cognition in persons with PD, independent of age, sex, race, education, and smoking history, the team reported in the journal, Movement Disorders (2013, Vol 28, 2: 176-182). Higher tibia bone lead concentration among PD patients was associated with worse performance on all of the individual telephone tests, especially tests of working memory and attention. Furthermore, they wrote, disease duration is unlikely to be a source of confounding in the data, because further adjustment for age at PD symptom onset did not change their findings.
This study is the first to identify an association between lead exposure and cognition among persons with PD. The results are also consistent with the possibility that lead exposure may lead to a particular form of PD that involves more-rapid onset of cognitive decline and dementia. If this represents a causal relationship, then, in addition to being a primary risk factor for PD, lead exposure would be among the few known modifiable risk factors for cognitive decline in general, and, potentially, PD-related dementia.