In a case-control study from Spain on the effects of smoking and alcohol use on the risk of Alzheimer’s Disease (AD), the authors found that the risk of AD was unaffected by any measure of tobacco consumption.  On the other hand, alcohol consumers showed a 47% lower risk of developing AD than did never consumers, with effects mainly among women and among never smokers.  No differences were noted by type of alcoholic beverage consumed.  
The authors conclude that mean daily total consumption of alcohol showed increasingly protective dose-response relationships in women.
The numbers in this analysis were rather small, and there is always the possibility of confounding by other lifestyle factors.  Still, the study supports a number of previous epidemiologic studies showing a lower risk of developing AD for moderate consumers of alcohol.
Reference: García AM, Ramón-Bou N, Porta M.   Isolated and joint effects of tobacco and alcohol consumption on risk of Alzheimer’s Disease.   Journal of Alzheimer’s Disease 2010;20:577–586. (DOI 10.3233/JAD-2010-1399).