Hi Tulip
I think it's gonna depend on how deficient you might be in these two minerals. You might need 50mgs, or you might need 20.
Are you taking a multi-mineral as well? I just mention that because sometimes taking higher doses of individual minerals for prolonged periods of time may cause an imbalance...
Zinc for example interacts with copper, and too much zinc can lower copper levels. Too much vitamin C can lower copper levels as well. Also magnesium and calcium work together, but also need other trace minerals in order to really work properly (like boron, vitamin d, vitamin K, strontium, etc....)
just my two pennies.
d.