What Is Calcium, and Where Do We Get It?
“Calcium is a mineral that the body needs for numerous functions, including building and maintaining bones and teeth, blood clotting, the transmission of nerve impulses, and the regulation of the heart’s rhythm. Ninety-nine percent of the calcium in the human body is stored in the bones and teeth. The remaining 1 percent is found in the blood and other tissues.
The body gets the calcium it needs in two ways. One is by eating foods or supplements that contain calcium. Good sources include dairy products, which have the highest concentration per serving of highly absorbable calcium, and dark leafy greens or dried beans, which have varying amounts of absorbable calcium. Calcium supplements often contain vitamin D; taking calcium paired with vitamin D seems to be more beneficial for bone health than taking calcium alone. (Read more about calcium and osteoporosis.)
The other way the body gets calcium is by pulling it from bones. This happens when blood levels of calcium drop too low, usually when it’s been awhile since having eaten a meal containing calcium. Ideally, the calcium that is “borrowed” from the bones will be replaced at a later point. But, this doesn’t always happen. Most important, this payback can’t be accomplished simply by eating more calcium.”
The benefits of calcium
“Your body needs calcium to build and maintain strong bones. Your heart, muscles and nerves also need calcium to function properly.
Some studies suggest that calcium, along with vitamin D, may have benefits beyond bone health: perhaps protecting against cancer, diabetes and high blood pressure. But evidence about such health benefits is not definitive.” 
6 other surprising health benefits of calcium
“You may have heard that calcium keeps your bones strong, but did you know that it boasts many other benefits as well? Here's how calcium keeps you healthy
It can help you lose weight
It fights colon cancer
It decreases your risk for type II diabetes
It makes you fertile
It helps you beat PMS symptoms
It keeps your mouth healthy” 
 Harvard School of Public Health - Calcium, what’s best for your bones and health.
 The Mayo Clinic - Calcium and calcium supplements: Achieving the right balance.
 Best Health Magazine Canada - 6 Surprising Health Benefits of Calcium