You would think simple atomic particles such as sodium, magnesium and iron would be evenly distributed throughout the body, and that their blood levels would tell us whether we have enough of them in our bodies.

I already knew that this was not the case with sodium or magnesium, but I recently learnt that the same situation exists with iron.

Low sodium can be associated with swelling of the brain and rapid neurological deterioration, but if it develops slowly, the brain may not suffer as much as if it happens acutely.

Magnesium is shuffled from our tissues into the blood stream if our serum levels drop, which means even people with normal serum levels can have severe intracellular magnesium deficiency.