Age obviously plays a big role. Maybe as we age you absorb fewer minerals. The body does all it can to keep the vital organs going at the expense of the other non-vital organs. It's the same thing that happens when one is exposed to freezing temperatures for a long time. The body shots down the circulation to the extremeties and as a result you would lose some toes so that you can stay alive longer. This way the vital organs can keep going longer.