This is specifically for "heavy drinking". In case folks are wondering how that's defined (per the study, computed based on volume of 60 g of ethanol), it's:
Not much for chronic alcohol abusers. Especially in countries where people produce their own wine and spirits. Every two-three hours one shot or glass of wine to take the edge off, calm the nerves. The person doesn't even look like an alcoholic, no tremors, just lowered inhibitions and inappropriate behavior. Come age 60 and they are at risk of early onset dementia. The ethanol dissolved the gray matter. Atrophy and enlarged ventricles clearly visible on brain scans.
People get dementia in their 50ies and 60ies, sometimes earlier. It's not the most common, but it happens. Also, the brain begins to degrade years before symptoms are noticed, usually subtle changes in behavior.
For reference that's 2/3 of a standard bottle of wine, or a little more if you drink white wine. And that would be a boot of german beer, or 3 1/3 pints of pale ale or lager.