Researchers find potential link between lifetime lead exposure and dementia

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Several studies indicate a downward trend in the incidence and prevalence of dementia, and researchers are now offering a new hypothesis suggesting the decline may be a result of generational differences in lifetime exposure to lead, according to a new study published in the Journal of Alzheimer's Disease.

Leaded gasoline was a ubiquitous source of air pollution between the 1920s and 1970s. As it was phased out, beginning in 1973, levels of lead in citizens' blood plummeted. Research from the 1990s indicates that Americans born before 1925 had approximately twice the lifetime lead exposure as those born between 1936 and 1945.

Lead is a known neurotoxin that crosses the blood-brain barrier. Animal studies and research on individuals occupationally exposed to lead suggest a link between lead exposure and dementia. Other studies have shown a higher incidence of dementia among older adults living closer to major roads and among those with a greater exposure to traffic related pollution.

For the current study, researchers were interested in a potential link between lifetime lead exposure and a recently identified subtype of dementia, Limbic-predominant Age-related TDP-43 Encephalopathy (LATE), whose pathological features have been identified in 20 percent of dementia patients over the age of 80.

Other plausible explanations for the improving trends in dementia incidence include higher levels of educational attainment, lower prevalence of smoking, and better control of hypertension among older adults today compared to previous generations. However, even when these factors are statistically accounted for, many studies still find incidences of dementia declining.

The authors suggest that next steps to assess the validity of this hypothesis could include comparing 1990s assessment of blood lead levels to current Medicare records, assessing lead levels in teeth and tibia bones, which serve as proxies for life-time exposure, when conducting post-mortems of brains for dementia, and examining the association between particular gene variants associated with higher lead uptake and dementia incidence.