Coffee helps erections? True or not true.

Another dinner discussion where the EF gang can weigh in.

We read that a cup of coffee (supposedly this does not work with caffeine soda like Coke, which to me makes NO sense), increases your blood flow ALL over...including the penis, and can help get a bigger, faster, harder erection if you are sleepy.

Any truth to that been experienced by anyone? If it IS true...why "only coffee"??? Some soda has WAY more caffeine, I thought.