Regarding the vitamin & sugar connection, I also think there can be a lot to that. Not the whole thing--but certainly a piece of the puzzle.
I personally feel that my AH has a type of craving that I have never experienced when it comes to alcohol. And that first drink sets off a biochemical (and behavioral) cascade.
But when armed with the knowledge of how he reacts in the presence of alcohol, he also has free will. One time he said "If I had cancer, you wouldn't judge me." And I said, "If you had cancer, you'd run for chemotherapy."
It's all about what we choose to do in the gap between knowledge and response.