Smoking and risk of dementia and Alzheimer's disease in a population-based cohort study: the Rotterdam Study.
BACKGROUND
Previous studies suggested a protective effect of smoking on Alzheimer's disease, but most were case-control studies based on prevalent cases. The findings of prospective studies on the association between smoking and the risk of dementia are inconclusive.


METHODS
We did a population-based follow-up study of elderly people who were initially free of dementia. 6870 people aged 55 years and older agreed to take part. Smoking history was taken at baseline and participants were classified as never smokers, former smokers, and current smokers. During follow-up, we recorded all incident cases of dementia. We used never smokers as the reference category to calculate relative risks of dementia and Alzheimer's disease by Cox proportional hazards regression, after adjustment for age, sex, education, and alcohol intake. We also examined modification of risk by age, sex, and the apolipoprotein E (APOE) genotype.


RESULTS
During mean follow-up of 2.1 (range 1.5-3.4) years, 146 incident cases of dementia were detected, of which 105 were Alzheimer's disease. Compared with never smokers, smokers had an increased risk of dementia (relative risk 2.2 [95% CI 1.3-3.6]) and Alzheimer's disease (2.3 [1.3-4.1]). Smoking was a strong risk factor for Alzheimer's disease in individuals without the APOEepsilon4 allele (4.6 [1.5-14.2]), but had no effect in participants with this allele (0.6 [0.1-4.8]).


CONCLUSIONS
Smoking was associated with a doubling of the risk of dementia and Alzheimer's disease. Our finding that carriers of the APOEepsilon4 had no increased risk of dementia suggests an interaction between smoking and the APOEepsilon4 genotype in the aetiology of Alzheimer's disease.
Ott
A
A
Department of Epidemiology & Biostatistics, Erasmus University Medical School, Rotterdam, The Netherlands.
Slooter
A J
AJ
Hofman
A
A
van Harskamp
F
F
Witteman
J C
JC
Van Broeckhoven
C
C
van Duijn
C M
CM
Breteler
M M
MM
D017677:Age Distribution; D000368:Aged; D000544:Alzheimer Disease / Q000209:etiology*; D053327:Apolipoprotein E4; D001057:Apolipoproteins E / Q000235:genetics; D016022:Case-Control Studies; D003704:Dementia / Q000209:etiology*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D015994:Incidence; D008297:Male; D009426:Netherlands; D011159:Population Surveillance; D016016:Proportional Hazards Models; D012107:Research Design; D012306:Risk; D012307:Risk Factors; D017678:Sex Distribution; D012907:Smoking / Q000009:adverse effects*
D053327:Apolipoprotein E4; D001057:Apolipoproteins E