Affiliations: Department of Preventive Medicine and Public Health,
Faculty of Medicine, University of Cordoba, Cordoba, Spain | Institute of General Practice & Primary Care,
University of Sheffield, Sheffield S5 7AU, UK
Note: [] Corresponding author. Mohamed Farouk Allam, Department of
Preventive Medicine and Public Health, Faculty of Medicine, University of
Cordoba. Avda. Menéndez Pidal, s/n Cordoba 14004, Spain. Tel.: +34 957
218 278; Fax: +34 957 218 573; E-mail: [email protected]
Abstract: Our aim was to estimate the pooled risk of current and former
smoking for Parkinson's disease (PD).We have reviewed all observational studies
that evaluated the association between PD risk and smoking habit. Twenty six
studies were identified: 21 case-control, 4 cohort and 1 cross-sectional. The
cross-sectional study did not compare former with never smokers. These studies
were carried out between 1968 and 2000. There was an obvious protective effect of current smoking in the
pooled estimate [risk estimate 0.37 (95% confidence interval 0.33 to 0.41)].
Former versus never smokers had pooled risk estimate of 0.84 (95% confidence
interval 0.76 to 0.92). Current and former smoking do not, therefore, exert the
same protective effect against PD so that it is unnecessary to postulate a
biological mechanism through which smoking protects against PD. The results
show that the reverse direction of causation is a more probable explanation,
i.e. movement disorders of PD protect against smoking. Another explanation is
that failure to develop strong smoking habits in early adult life might be a
prodromal symptom of the disease and could perhaps be its first clinical
manifestation.
