CIGARETTE-SMOKING AND PROTECTION FROM PARKINSONS-DISEASE - FALSE ASSOCIATION OR ETIOLOGIC CLUE

We reviewed 46 published reports associating cigarette smoking and Par kinson's disease. Although the majority indicated an approximate halvi ng of smoking frequency in persons with Parkinson's disease, many obse rvers have suggested that the effect could be a spurious result. That the association may be real is suggested by at least six observations: (1) the consistency of findings between independent studies of differ ent design, conducted by different investigators, in different nations , over 35 years; (2) the association's predominance and strength in pr ospective studies; (3) the apparent detection of a dose-response relat ion; (4) the inability to explain the association by confounding varia bles; (5) the flaws in certain arguments against the association's val idity; and (6) the identification of a similar association, of similar magnitude, between smoking and reduced occurrence of Alzheimer's dise ase. A protective association of cigarette smoking for Parkinson's dis ease may constitute an important etiologic clue.