I know I sound like a pest... but you really need the actual B12 numerical result. Do not accept "normal" because in US the lab ranges are out of date and report lows as normal which the doctors then tell their patients. So therefore a level of 250 will be not flagged in US, however it is a seriously low level biologically.

You need to be at least at 400 US units. This level now appears in medical websites targeting doctors, for continuing ed.

Alcohol metabolism results in formation of by products which in some people are toxic. These are primarily aldehydes. So you don't have to be a heavy abuser (which often has poor diet associated), to have reactions. This is why the benfotiamine is useful for those drinkers. There are also congeners in it which people may react to.

http://banderasnews.com/0506/rr-congeners.htm

Also chronic alcohol use (doesn't have to be heavy) will have that diuretic effect and therefore cause losses in magnesium.
So taking a good magnesium supplement or eating foods rich in it may help. Poor magnesium levels are implicated in PN symptoms (nerve malfunction) in some people, and are very bad for health because about 300 systems use it as a cofactor. Estimates are that about 70% Americans are low in this vital mineral. Do not accept magnesium OXIDE however, as it is not absorbed, and is basically a laxative.