My body doesn't seem to absorb some nutrients properly, no matter how much of it is present in the food I eat.
For example, my diet has PLENTY of potassium, and my blood tests always show adequate levels. Yet i will have regular cramps unless I supplement too. I just figure my potassium requirements are higher than 'average', or i absorb less of it.
I currently taking
Vit D3 (to combat chronic deficiency) with K2 to help the D3 work
Natural source vit C