The American Association of Endocrine Surgeons, Patient Education Site

Parathyroid Glands: Vitamin D and calcium levels

Does vitamin D affect calcium levels and the parathyroid glands?

Vitamin D helps the intestines absorb calcium. However, the vitamin D must first be activated or "turned on" by parathyroid hormone (PTH). Once activated, vitamin D acts to greatly increase the amount of calcium that the intestines can absorb from food, sometimes by as much as two to four times. The body can either make its own vitamin D using a process that requires sunlight or obtain vitamin D directly from the diet (e.g. in fortified milk or vitamins). Many people across the world have vitamin D deficiency — experts estimate that one-third of Americans are vitamin D deficient.

For patients with vitamin D deficiency, it is difficult for the body to obtain calcium from the diet. This often leads to a rise in the PTH level, since the parathyroid glands must increase the PTH production in order to increase calcium levels by "stealing" it from the bones. Therefore, people with a normal blood calcium levels and a high PTH level may have secondary hyperparathyroidism(see Special Cases: Secondary Hyperparathyroidism), which means that the high PTH level is a normal response of healthy parathyroids glands to another problem (like vitamin D deficiency or kidney failure).

It is quite common for a person to have both primary hyperparathyroidism and vitamin D deficiency, since primary hyperparathyroidism can lead to decreased vitamin D stores. This can sometimes make it difficult to establish the diagnosis of primary hyperparathyroidism. It is generally advisable to have the blood vitamin D levels checked during the work-up of parathyroid disease. For people who may have both primary hyperparathyroidism and vitamin D deficiency, some are best treated with surgery first, and others are best treated with vitamin D first. This decision should be made with your physician.

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