Introduction McIntyre Powder (MP), a fine-sized aluminum and aluminum compound powder, was administered to Ontario miners from 1943 to 1979 as purported prophylaxis against silicosis. Aluminum has long been suspected of having a role in the development of neurological diseases. However, very few studies have examined the risk of neurological disease among miners with exposure to aluminum dust, and previous findings were inconclusive.

Objectives We estimated associations between respirable aluminum exposure through MP and neurological disease in a retrospective cohort of mining workers from Ontario, Canada. Outcomes included Alzheimer’s disease, Alzheimer’s with other dementias, Parkinson’s disease, parkinsonism, and motor neuron disease.

Methods The cohort was created by linking a database of mining workers’ work history to health care records. This analysis included 36,826 male miners potentially exposed to MP between 1943 and 1979, followed up for disease diagnosis between 1992 and 2018. Exposure was assessed using two approaches, self-reported and historical records. Neurological diseases were ascertained using physician billing and hospital discharge records. Poisson regression models were used to estimate associations between MP exposure and neurological outcomes using incidence rate ratios and 95% confidence intervals (RR, 95% CI).

Results Exposure to self-reported MP was associated with an elevated incidence rate of Parkinson’s disease (RR 1.34, 95% CI: 1.14, 1.57). The rate of Parkinson’s disease appeared to increase with the duration of exposure assessed by historical records. Ever-exposure to MP was positively associated with an elevated rate of Alzheimer’s with other dementias (RR 1.12, 95% CI 1.06, 1.19), but not Alzheimer’s disease alone.

Conclusion This study found that miners who were exposed to respirable aluminum, as McIntyre Powder, had elevated rates of Parkinson’s disease. The rate of Parkinson’s disease appeared to increase with the duration of exposure assessed by historical records.