Occupational risk factors in Alzheimer's disease:: a review assessing the quality of published epidemiological studies

Epidemiological evidence of an association between Alzheimer's disease (AD) and the most frequently studied occupational exposures - pesticides, solvents, electromagnetic fields (EMF), lead and aluminium - is inconsistent. Epidemiological studies published up to June of 2003 were systematically searched through PubMed and Toxline. Twenty-four studies ( 21 case - control and 3 cohort studies) were included. Median GQI was 36.6% (range 19.5 - 62.9%). Most of the case - control studies had a GQI of <50%. The study with the highest score was a cohort study. Likelihood of exposure misclassification bias affected 18 of the 24 studies. Opportunity for bias arising from the use of surrogate informants affected 17 studies, followed by disease misclassification ( 11 studies) and selection bias ( 10 studies). Eleven studies explored the relationship of AD with solvents, seven with EMF, six with pesticides, six with lead and three with aluminium. For pesticides, studies of greater quality and prospective design found increased and statistically significant associations. For the remaining occupational agents, the evidence of association is less consistent ( for solvents and EMF) or absent ( for lead and aluminium).