People with various intestinal malabsorption disorders, including Crohn's disease, are more prone to develop vitamin D deficiency due to their inability to absorb this fat-soluble vitamin.

Vitamin D deficiency causes a decrease in ionized calcium in
blood. This leads to an increase in the production and secretion of parathyroid hormone (PTH).

PTH stimulates the mobilization of calcium from the skeleton, reduces loss of calcium from the kidneys, and causes increased excretion of phosphorus from the kidneys. The result is a normal fasting serum calcium, and a low, or low-normal, serum phosphorus.

So, vitamin D deficiency is characterized biochemically by either a normal, or low-normal, serum calcium with a low-normal, or low-fasting, serum phosphorus and an elevated serum PTH.

You will not wind up with too much calcium in your bloodstream by receiving the needed vitamin D, because, right now, your vitamin D deficiency is causing a cascade of hormonal activity that is taking calcium from your bones in order to maintain a chemical balance in your blood-and, you sure don't want this "borrowing" of calcium from your bones to continue!

Hope