Parathyroid hormone

Parathyroid hormone is a natural substance your body makes in four tiny glands in your neck. These glands sit behind the thyroid gland. The hormone's main job is to control the amount of calcium in your blood. Calcium is a mineral your body needs for strong bones, working muscles, and healthy nerves.

When the calcium in your blood gets too low, the glands release this hormone. It tells your bones to release some stored calcium, tells your kidneys to hold onto calcium instead of flushing it out, and helps your body absorb calcium from food. Scientists have also made medicines from this hormone. These medicines are given as shots and can help build new bone in people whose bones are weak and break easily.

Most of what we know comes from studies of the injectable medicine, and its safety over very long use is still being studied. Researchers are also working on pill forms, because shots can be hard for people to take every day, but oral versions are still being tested. Anyone thinking about using it should talk to a doctor first, since changing calcium levels can be dangerous.