I also agree with the caffeine thing. The reason I stay off it is not so much the immediate effect of caffeine on anxiety (I find none), but because caffeine increases mania. Ultimately mania (dealing with life frantically) causes the nervous system to respond poorly. And anxiety seems to be above all a disproportionate reaction of the sympathetic nervous system. There is also an effect on sleep regulation and a hard edge to withdrawal that can exacerbate anxiety. Incidentally, chocolate contains a related compound, but not caffeine itself. I've experimented with chocolate over what I would consider to be statistically significant periods of time, and I honestly couldn't detect any effect in moderation. Your mileage may vary.