Calcium makes our bones strong.
Bones tend to lose calcium when they stop doing work.
Calcium is essential to maintaining strong bones. Its loss weakens bones and causes them to break more easily. Calcium loss can also increase the threat of kidney stones as the mineral is excreted. Some humans have a tendency to lose calcium in their bones as they age. Running and jumping are not as effective in space as they are on Earth because a person's weightless limbs can provide little resistance.