It takes Vitamin B to "digest" the coffee. Same as with beer :-) Doesn't matter when they're taken; if you haven't taken your B vitamin before you drink your coffee, it will just "use" what B you have in your body. That's the "problem." But taking additional, since B is a water soluable vitamin, if your pee turns yellow you have "too much" for your body to use so heck, I don't mind "wasting" mine on a little coffee in the morning, I need my coffee almost as much as I need my B

Look at paragraphs 2 and 3 of this: http://www.ajcn.org/cgi/content/full/79/5/713