The parathyroid glands are four glands at the front and base of the neck at the 4 corners of the thyroid gland. These glands produce the parathyroid hormone that regulates the calcium, phosphorus, and magnesium balance within the blood as well as normal bone mineralization.
Source: GreenFacts
Excessive production of this hormone caused by increased activity of these glands is known as hyperparathyroidism. When this occurs in response to low blood calcium caused by another condition, the condition is called secondary hyperparathyroidism. This is seen when vitamin D levels are low or when calcium is not absorbed from the intestines. Correcting the calcium level and the underlying problem will bring the parathyroid levels in the normal range.
Source: GreenFacts