Why is Vitamin D important and how does it relate to the parathyroid glands?

Vitamin D (Vit D) is important for the regulation of calcium and phosphorus levels in the body. Some foods are fortified with vitamin D, such as milk and eggs. The primary source of vitamin D, however, is sunlight. While excessive sun exposure is not recommended, some exposure to sunlight (approximately 10 minutes a day on average) is necessary to supply with body with vitamin D. Vitamin D is initially formed in the skin after sun exposure. That vitamin D molecule must then travel through the liver and kidneys to be processed into its active form.

Vitamin D increases calcium levels in the blood through several actions. Vitamin D helps the body absorb calcium from the food we eat while the food is being digested in the intestines. Vitamin D also prevents too much calcium from being lost in the urine, helping the body hold on to the calcium it already has. Without vitamin D, calcium levels fall too low, and the body must find a way to raise the serum calcium level (the level of calcium in the blood) back to the required level. This is done by the parathyroid glands.

The parathyroid glands are small, pea-shaped glands located in the neck that make parathyroid hormone. Parathyroid hormone, like vitamin D, functions to raise the serum calcium level. They do this, however, in different ways. Parathyroid hormone first tries to increase the amount of vitamin D by increasing the amount processed by the liver and kidneys. It cannot, however increase the amount of vitamin D that is formed in the skin, so sun exposure or vitamin D supplements are still necessary.

Secondly, parathyroid hormone raises calcium in the blood by removing it from the bones. Calcium is an important part of bones and is necessary to provide strength to the bones. When the serum calcium level remains low for long periods of time, the parathyroid glands continuously produce high levels of parathyroid hormone, which keeps removing calcium from the bones. This will eventually lead to osteopenia, the condition of weak or brittle bones that fracture easily. This example illustrates why vitamin D is so important.