Parathyroid glands and vitamin D When most people think of calcium, they think it’s most important for bone health. But actually, calcium is most important for your nervous and muscular system. Your body needs a narrow range of serum calcium in your blood, or otherwise you couldn’t function and you wouldn’t survive. Your bones act as a reservoir for calcium, providing calcium for your blood when serum calcium (calcium in the blood) is low. So how does your body make sure it has the right amount of calcium in the blood? This involves vitamin D, calcium and a hormone called parathyroid hormone. The parathyroid glands are endocrine glands located in your neck near your thyroid glands (but no functional relation to). Their job is to secrete parathyroid hormone (PTH). PTH regulates serum calcium and phosphate, which in return regulate PTH. Your kidney produces vitamin D’s active form, which is called 1,25(OH)₂D. How much 1,25(OH)₂D your kidney decides to produce depends on how much PTH and calcium are in your body, but you also need good vitamin D intake to be able to produce adequate 1,25(OH)₂D. 1,25(OH)₂D helps you absorb calcium and also keeps your PTH levels in check.
This is how it all happens: When calcium in your blood is low, your parathyroid starts secreting PTH. PTH starts pulling calcium from your bones and into your blood. PTH also starts telling your kidneys to start making more 1,25(OH)₂D. You have vitamin D stores in your body called 25(OH)D that are ready for the kidney to produce 1,25(OH)₂D when needed, if you get adequate vitamin D intake. When the kidney starts producing 1,25(OH)₂D, it helps the gut absorb more calcium than usual, to make sure you get enough calcium into your body. When 1,25(OH)₂D increases and helps your body get to the right calcium balance, it tells your parathyroid to stop making so much PTH, and stop pulling calcium from your bones. On the other hand, when calcium in the blood is high, your parathyroid won’t release much PTH at all. The amount of calcium in your blood tells your parathyroid not to release any PTH, and in turn, PTH doesn’t tell your kidney to produce more 1,25(OH)₂D.
So you stop absorbing too much calcium and allows your body to lower its blood calcium. This interaction between calcium, parathyroid and vitamin D is happening constantly; 1,25(OH)₂D and PTH always adjusting to make sure you have the right calcium balance. When you get enough vitamin D from good sun exposure and supplementation habits and enough calcium from your diet, this allows you to maintain a healthy calcium level in your blood and keep good amounts of calcium in your bones. Healthy vitamin D and calcium habits also help keep your PTH levels in check. Don’t get too much vitamin D, though! While getting too little vitamin D will cause PTH to be too high and lead to poor bone health, getting too much can also be bad for your health. When your body gets too much vitamin D, it absorbs too much calcium and makes your calcium levels in the blood too high. This is called hypercalcemia. See our page, How do I get the vitamin D my body needs? Sometimes PTH can be too high or too low in certain conditions that affect the parathyroid, making getting the right amount of vitamin D really important.
These conditions are called hyperparathyroidism and hypoparathyroidism. Hyperparathyroidism is excessive secretion of PTH, or over-activity of parathyroid glands. There are two main types of hyperparathyroidism: primary and secondary. In these conditions, it’s important to work with a doctor to decide the best course of action to make sure your body has the right balance of vitamin D, calcium and PTH. In primary hyperparathyroidism, the parathyroid glands have gone “haywire.” The most common reason for this is because of a non-cancerous tumor on the parathyroid, called an adenoma. Because of the adenoma, the parathyroid can make too much PTH, which can cause calcium to be too high in the blood, and overtime, lead to poor bone health. Sometimes doctors decide to treat primary hyperparathyroidism surgically, by removing the adenoma. If you have primary hyperparathyrodism, you need to work with your doctor to see if you can take vitamin D. Since you may have high blood calcium, it’s important to make sure you’re under a doctor’s supervision if considering taking vitamin D.
Secondary hyperparathyroidism is caused by either long term vitamin D deficiency or kidney failure. With long term vitamin D deficiency, the body may not get enough vitamin D to absorb adequate calcium and keep PTH levels in check, leading to high PTH levels. This can be corrected by treating vitamin D deficiency. In kidney failure, sometimes the kidney has difficulty producing 1,25(OH)₂D, which can lead to poor absorption of calcium, low blood calcium, and too much PTH. Overtime, secondary hyperparathyroidism can lead to poor bone health, so it’s important to treat. If you have secondary hyperparathyrodism, you need to work with your doctor to see how much vitamin D you should be taking and if you need to take any other course of action, like taking activated vitamin D. Hypoparathyroidism is a disorder where there is too little parathyroid activity, where the parathyroid doesn’t make as much PTH as it should. The most common cause of hypoparathyrodism is surgical removal of a part of your parathyroid.
This can happen in two ways: Hypoparathyroidism can cause you to not having enough calcium in the blood, a condition called hypocalcemia, but this doesn’t always happen. Because of this, vitamin D supplementation can be very important in making sure you have the right balance of calcium in the blood. It’s important to work with your doctor if you have hypoparathyroidism, to see how much vitamin D you should be taking and if you may need to take any other course of action. Dusso AS and Tokumoto M. Biological and Molecular Effects of Vitamin D on the Kidney. In Vitamin D: Physiology, Molecular Biology and Clinical Applications (Second Edition), by Holick MF, 2010. Holick, MF et al. Guidelines for preventing and treating vitamin D deficiency and insufficiency revisted. Journal of Clinical Endocrinology & Metabolism, 2012. Silver, J and Naveh-Many T. Vitamin D and the Parathyroids. In Vitamin D: Physiology, Molecular Biology and Clinical Applications (Second Edition), by Holick MF, 2010.