Magnesium. You should take magnesium any time you take calcium, since they need to be in balance, but when I get cramps it's much more likely to be magnesium that's the culprit.
Speed comes from what you put behind you. - Judi Ketteler
Magnesium worked for me when I had that issue. I don't think I've gotten a single nighttime foot cramp since I started taking it.