Reviving this thread with something I just learned.
Potassium and magnesium compete for uptake, and therefore should not be taken at the same time. When shopping for supplements, I found several brands that nonetheless combined potassium and magnesium, and indeed, my current brand of potassium uses magnesium stearate as a filler.
Calcium is another mineral that limits the absorption of others, and should not be taken in combination with potassium, magnesium, zinc. Yet calcium is a very common filler for other minerals.
This is making me re-thing the usefulness of a daily multi-vitamin, especially since my diet is heavy in greens and raw vegetables.
What do you guys think?