smoking and PD

[mschild <mmoo@xxxxxxxxxxx>]

Duration of Smoking, not Intensity, Reduces PD Risk

Smoking has long been associated with a reduced risk of Parkinson's disease. A 
new study indicates the effect correlates with number of years a person smokes, 
not how much tobacco is consumed over that time.

The study population comprised over 300,000 participants in the NIH-AARP Diet 
and Health Cohort, a long-range study of the effect of diet and lifestyle on 
cancer risk. Of these, 1,662 had a confirmed PD diagnosis after 1995. 

Thirty-nine percent of non-PD subjects, and 43% of PD subjects, had never 
smoked. Just over half of each group had smoked in the past. Current smokers 
made up 9.8% of those without PD, versus 5.2% of PD patients.

The authors report, "Compared with never smokers, the multivariate odds ratios 
were 0.78 [i.e., risk reduced by 22%] for past smokers and 0.56 for baseline 
current smokers." Among past smokers, risk was lowest for those who had quit 
most recently.

When both number of cigarettes per day and years smoking were considered 
together, the number of cigarettes "was no longer significantly associated with 
PD risk." When changes in individual smoking history over the lifetime were 
analyzed, "Starting from earlier 20s, being a smoker in each of the life 
periods was associated with a lower PD risk.; however, those smoking more than 
20 cigarettes per day did not have a lower risk of PD than participants 
smoking less."

Regarding the failure of short-term trials of nicotine to have any beneficial 
effect on PD, the authors state "the current study suggests that years of 
smoking (and hence nicotine administration) may be needed for any reduction of 
PD risk."

An editorial by Beate Ritz and Shannon Rhodes accompanies the study.


Smoking duration, intensity, and the risk of Parkinson disease
H Chen, X Huang, X Guo, et al.
Neurology 2010;74:878-884

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