Calcium is a mineral that helps make strong bones and teeth. Most of the calcium in your body is in your bones. It takes about 25 to 30 years for your bones to reach their maximum size and strength (peak bone mass). When you are younger, taking in enough calcium helps you build strong bones. When you are older, getting enough calcium in your diet helps limit bone loss. Your body can't make calcium, so you must get it from foods or supplements.