Pooled analysis of tobacco use and risk of Parkinson disease.
BACKGROUND
Epidemiologic studies have reported that cigarette smoking is inversely associated with Parkinson disease (PD). However, questions remain regarding the effect of age at smoking onset, time since quitting, and race/ethnicity that have not been addressed due to sample size constraints. This comprehensive assessment of the apparent reduced risk of PD associated with smoking may provide important leads for treatment and prevention.


OBJECTIVE
To determine whether race/ethnicity, sex, education, age at diagnosis, and type of tobacco modify the observed effects of smoking on PD.


METHODS
We conducted the first ever pooled analysis of PD combining individual-level data from 8 US case-control and 3 cohort studies (Nurses' Health Study, Health Professionals Follow-Up Study, and Honolulu-Asia Aging Study) conducted between 1960 and 2004. Case-control studies provided data for 2328 PD cases and 4113 controls matched by age, sex, and ethnicity; cohort studies contributed 488 cases and 4880 controls selected from age- and sex-matched risk sets.


METHODS
Incident PD.


RESULTS
We confirmed inverse associations between PD and smoking and found these to be generally stronger in current compared with former smokers; the associations were stronger in cohort than in case-control studies. We observed inverse trends with pack-years smoked at every age at onset except the very elderly (>75 years of age), and the reduction of risk lessened with years since quitting smoking. The risk reductions we observed for white and Asian patients were not seen in Hispanic and African American patients. We also found an inverse association both for smoking cigars and/or pipes and for chewing tobacco in male subjects.


CONCLUSIONS
Our data support a dose-dependent reduction of PD risk associated with cigarette smoking and potentially with other types of tobacco use. Importantly, effects seemed not to be influenced by sex or education. Differences observed by race and age at diagnosis warrant further study.
Ritz
Beate
B
Department of Epidemiology and Environmental Health Sciences, UCLA School of Public Health, 650 Charles Young Smith Dr S, Los Angeles, CA 90095-1772, USA. britz@ucla.edu
Ascherio
Alberto
A
Checkoway
Harvey
H
Marder
Karen S
KS
Nelson
Lorene M
LM
Rocca
Walter A
WA
Ross
G Webster
GW
Strickland
Daniel
D
Van Den Eeden
Stephen K
SK
Gorell
Jay
J
D017677:Age Distribution; D017668:Age of Onset; D000368:Aged; D016022:Case-Control Studies; D015331:Cohort Studies; D015897:Comorbidity; D004305:Dose-Response Relationship, Drug; D005006:Ethnicity; D005260:Female; D006801:Humans; D008297:Male; D015201:Meta-Analysis as Topic; D008875:Middle Aged; D016017:Odds Ratio; D010300:Parkinson Disease / Q000453:epidemiology* / Q000208:ethnology / Q000503:physiopathology; D044469:Racial Groups; D012307:Risk Factors; D017678:Sex Distribution; D016540:Smoking Cessation / Q000208:ethnology / Q000706:statistics & numerical data; D014029:Tobacco Use Disorder / Q000453:epidemiology* / Q000208:ethnology / Q000503:physiopathology