Calcium and Vitamin D
The primary source of vitamin D in our bodies comes from our diet. In addition, vitamin D is produced in our skin when exposed to the sun. Vitamin D from our diet or skin goes through an initial activation step in the liver where an enzyme (25-hydroxylase) converts vitamin D into 25-hydroxy-vitamin D. The next step in activation occurs in the kidneys where another enzyme (1-alpha-hydroxylase) converts 25-hydroxy-vitamin D into 1,25 dihydroxy-vitamin D (1,25 vit D), which is the active form. The 1,25 vit D regulates calcium levels in the blood by enhancing calcium absorption from our intestines and by increasing bone resorption to maintain a normal calcium level in the blood.
In patients with sarcoidosis, the granulomas contain cells called macrophages. Macrophages can have the enzyme 1-alpha-hydroxylase that converts vitamin D to its final active product, which then works to increase calcium levels in the blood and/or urine. About 5 percent of sarcoidosis patients have elevated calcium levels in their blood, and about 15 percent have elevated calcium levels in their urine. Chronically elevated calcium levels can increase the risk of developing kidney stones, can potentially affect kidney function, and weaken bones.
Your doctor usually checks your blood calcium level by doing routine blood tests and your urine calcium levels by checking the calcium levels in a 24 hour collection of urine. Your doctor may perform other tests to make sure there is no other cause for your elevated calcium levels.
If the calcium level is elevated in the blood and/or urine, then initial conservative measures such as decreasing vitamin D and calcium intake from diet or supplements and avoiding excessive sun exposure can potentially reduce the calcium levels. If these measures do not control the calcium level, then your doctor might start a medication to help control the calcium levels.