Diseases of the parathyroid gland can disrupt the production and release of the parathyroid hormone. In some cases, too much parathyroid hormone may be released, which is often caused by a condition known as hyperparathyroidism. As more calcium is allowed to enter the bloodstream, bones can become less dense, and this may result in conditions such as osteoporosis.
There are also instances in which the parathyroid glands do not produce enough parathyroid hormone. When this occurs, there is not enough calcium in the bloodstream for the muscles and brain to function properly, while bones and connective tissues start to deteriorate and become weak. When the body's calcium levels begin to drop, this can cause a variety of symptoms including numbness and tingling in the extremities, muscle cramps and spasms, and the feeling of "pins and needles" throughout the body.