Too little calcium in the body can cause tetany. This is a serious condition where the low level of calcium in the blood causes painful, long lasting muscle contractions that can be serious. Too little calcium can also cause osteoporosis. Women after the age of menopause are at high risk for this condition. The bones weaken and become brittle and can easily fracture. Height is lost and posture can become stooped. Older men are also at risk for this condition. Too much calcium can be dangerous. If kidney function begins to decline, excess calcium that the bones didn't use becomes difficult to excrete. That, along with excess phosphorus can lead to calcifications(hard deposits) forming in soft tissue in the body. These can block blood vessels, cause heart and lung disease and joint pain. Whenever homeostasis is upset in the body, the results can be life-threatening.
Blood needs to have calcium since it is responsible for the transmission of messages by the nerves, for muscle contractions and for blood to clot. A decline of blood calcium level will enable the parathyroid gland, located in the throat to release parathyroid hormone, which has the capacity to activitae osteoclast. Then osteoclasts or bone-destroying cells would break down bone matrices to release calcium in the blood.
However, if there is too much blood calcium level, also known as hypercalcemia, the excess amount of calcium are just deposited into bone matrix as hard calcium salts.