Parathyroid hormone is secreted by the parathyroid glands, endocrine glands located in the upper neck area of the human body. This hormone helps regulate the levels of calcium within the blood and the bones by stimulating the secretion vitamin D, a steroid hormone which helps in calcium absorption. Parathyroid hormone and vitamin D are related by their functions of regulating calcium stores, which are essential for healthy bones and cells. Problems with the parathyroid glands can occur in some individuals, which directly affects vitamin D secretion and ultimately the healthy regulation of calcium around the cells.
Many of the metabolic pathways that work to stimulate calcium secretion and absorption through the parathyroid hormone remain relatively unclear to researchers. It is known, however, that parathyroid hormone and vitamin D work together to accomplish the goal of regulating blood and bone calcium. Normal vitamin D, when obtained through the sun or diet, is converted into an active form the body can use and provides the main function of moving calcium into the bones for strengthening, building, and repair. Without sufficient vitamin D, the bones can become brittle and a person can develop osteoporosis due to too little calcium absorption.
The parathyroid hormone, through means not fully known, stimulates the secretion of the active form of vitamin D from the kidney, where it is usually stored. Parathyroid hormone and vitamin D work together to stimulate the making of a calcium-binding protein within the blood and around the cells. This protein will bind to calcium receptors and facilitate the movement of calcium into the appropriate places within the body. These places include the cells, blood, and bones, as well as in the intestines. The parathyroid can then prevent the loss of calcium in the urine, conserving blood calcium so that it can move to the appropriate destinations.
In many cases in which a patient is suffering from problems with the parathyroid glands, his or her body can lose calcium through the urine, resulting in too little blood calcium. This can also lead to brittle bones, as the bones are not receiving the supply of calcium ions needed for proper formation. In many such patients, vitamin D levels are often lower than normal, indicating that this may be one of the problems related to a parathyroid disorder. Although not proven, many researchers believe that parathyroid hormone and vitamin D problem cases may be helped with vitamin D supplementation.