Isolated and joint effects of tobacco and alcohol consumption on risk of Alzheimer's disease.

The roles of smoking and alcohol on the development of Alzheimer's disease (AD) remain unclear. We performed a case-control study on the effects of both exposures before the age of onset of the disease in the cases (and same reference age for their age-matched controls) on disease risk. Interviews were conducted with population controls (n=246) and relatives of cases (n=176) identified through local Alzheimer's Disease Associations. Logistic regression models were built adjusting by gender, age, residence, education, economic situation, employment, and history of dementia in close relatives. Risk of AD was unaffected by any measure of tobacco consumption. Alcohol consumers showed a lower risk of AD than never consumers (adjusted odds ratio, aOR = 0.53, 95% CI 0.32, 0.88), with differences by gender (women aOR =0.48, 95% CI 0.27, 0.84; men aOR=0.80, 95% CI 0.23, 2.80). Mean daily total consumption of alcohol and time consuming alcohol showed increasingly protective dose-response relationships in women. Lower AD risk was observed in alcohol drinkers of both genders who never smoked (aOR= 0.37, 95% CI 0.21, 0.65). All these associations were independent of the presence of apolipoprotein E4 allele(s) in the cases. Although the sample was small for some analyses addressing these interactions, our results suggest a protective effect of alcohol consumption, mostly in non-smokers, and the need to consider interactions between tobacco and alcohol consumption, as well as interactions with gender, when assessing the effects of smoking and/or drinking on the risk of AD.