There are three calcium regulating hormones in humans that play a critical role in regulating the calcium level in the body and maintaining healthy bones. These hormones are parathyroid hormone, calcitriol, and calcitonin. Parathyroid hormone stimulates bone formation and bone resorption and maintains the level of calcium in the body. Calcitriol, which is produced from vitamin D, stimulates the intestines to absorb sufficient amounts of calcium and phosphorus and also has a direct effect on bones. Calcitonin is responsible for inhibiting the breakdown of bones and protecting the body against abnormally high calcium levels.