The "protective" influence of cigarette smoking on Alzheimer's and Parkinson's diseases. Quagmire or opportunity for neuroepidemiology?
The negative association between smoking and both Alzheimer's (AD) and Parkinson's (PD) diseases is a consistent epidemiologic finding. This observation has prompted many investigators to conclude that cigarette smoking must be "biologically protective" against AD and PD. Rather than suggesting some as-yet-undefined pathogenetic clue, however, this negative association more likely is indicative of the under-appreciated influence of differential survival in epidemiologic studies.
Department of Neurology, West Virginia University School of Medicine, Morgantown, USA.