Can Alcohol Use or Abuse Cause or Aggravate Alzheimer's Disease?

While the MIND diet promotes moderate consumption of red wine as a preventative for Alzheimer's disease, we understand that chronic alcohol abuse can produce dementia-like symptoms.  So some (including me) wonder if chronic alcohol abuse can actually trigger the onset of Alzheimer's disease or if it can promote its progress.  I found a couple of studies that attempt to answer these questions.

This week, the journal Alzheimer's and Dementia published a study entitled "Association between alcohol consumption and Alzheimer's disease: A Mendelian randomization study."  The study looked at several different ways in which the progress of Alzheimer's disease and chronic alcohol abuse might be intertwined with each other that had (to me) some surprising results.

I wasn't willing to pay $36 to buy the article, and so I was unable to understand their methodology.  But I was able to read the synopsis.  They concluded the following:

• There was no association of alcohol consumption, alcohol dependence, or diagnosed alcohol use disorder with the occurrence of older onset (sporadic) Alzheimer's disease.  (Older onset Alzheimer's disease is the common type that becomes symptomatic at age 65 or later.)  
• The study identified an apparent protective effect of alcohol with respect to the age of onset survival for Alzheimer's disease (how long a subject lived after onset), but the researchers believed this was likely due to "survivor bias."  In other words, alcohol abuse could have eliminated part of the study population in a way that made those counted at the end of the study unrepresentative of the study population as a whole. 

Reading what I could of similar studies led me to an older study that pointed to some somewhat different conclusions.  This study was published in the journal Current Alzheimer's Research on July 25, 2017.  The study was entitled "The association between alcohol use and the progression of Alzheimer's disease," and it involved 360 early-stage Alzheimer's patients followed over 19 years.  (I'm not sure how many remained "early stage" throughout the study.)

The researchers tried to address a popular model of the disease from the time, that alcohol use and incidence of Alzheimer's disease could be depicted with a "U-shaped" curve.  In the curve, both non-drinkers and heavy drinkers experienced near-equal risk of developing the disease on their respective ends of the curve, while moderate drinkers in the middle received a protective effect.  The researchers wanted to determine if this picture might be more complicated than a simple relationship in which X amount of drinking equals Y probability of developing Alzheimer's disease.

For example, if moderate drinkers tended to drink red wine, and heavy drinkers drank beer and hard liquor, moderate drinkers would receive an unequal benefit from the resveratrol in red wine.  Resveratrol has nothing to do with alcohol content of the wine, but it appears to retard the development of Alzheimer's disease.

So what did they find?

• Cognition declined significantly faster in heavy drinkers than in moderate drinkers.  (Nothing in the paper suggested an effort to control for the cognitive effects due to alcohol abuse as differentiated from Alzheimer's disease, but I'm not sure how they would do that.) 
• They didn't find a significant difference in the rate of decline between mild-moderate drinkers and abstainers (like me).  So much for the U-shaped curve.
• All other factors being equal, subjects who consumed hard liquor declined more rapidly than those who consumed beer and/or wine.

So does drinking cause or aggravate Alzheimer's disease?  I guess it depends on who you ask.