Calcium is another one of the major minerals in the body and almost every cell uses calcium in some way. It helps muscles relax and contract; we all know our heart couldn't function without doing that. It is one of the most vital minerals for optimal cellular functioning, and the body keeps levels between a very narrow range.
Calcium is a cellular cement for bones and contributes to proper blood clotting. A decrease in calcium can lead to muscle cramps. As well, muscle twitches are due to insufficient calcium that helps with normal impulses (the messages between nerve fibres).
Did you know that as calcium levels drop the parathyroid hormone PTH sends the signals to release more calcium into the blood and helps to activate vitamin D which increases intestinal calcium absorption. Okay, I just find that fascinating (bit of a biology science nerd).
As we age we absorb less and less calcium from our diet and thus require more from our stores in our bones. Certain medicines, like antacids, also decrease calcium absorption and therefore more has to come from our bone stores. Too much calcium depletion in bones leads to osteoporosis and osteopenia.
So you can see how important it is to have your cellular calcium functioning at optimum levels and why it's a major mineral.