Hyperparathyroidism is an excess of parathyroid hormone in the bloodstream caused by overactivity of one or more of the body's four parathyroid glands. The parathyroid glands produce parathyroid hormone, which helps maintain an appropriate balance of calcium in the bloodstream and in tissues that depend on calcium for proper functioning. Hyperparathyroidism can cause hypercalcemia, osteoporosis, kidney stones but it can not cause gallbladder disease.