There is still the question of why so many people are deficient in B12, D, iron, and magnesium. Is it because they don't eat enough of those specific vitamins/m

There is still the question of why so many people are deficient in B12, D, iron, and magnesium. Is it because they don't eat enough of those specific vitamins/minerals or is it because their kidneys/livers/other organs have been damaged by a modern diet or by stress or through environmental pollutants. I'm willing to bet that in developed nations, it is less deficiency of vitamins or minerals in diet and more a defect of the body.