How Can One Be Severely Vitamin D Deficient But Still Have Normal Levels Of Calcium?

Question

Asked by MERF

How Can One Be Severely Vitamin D Deficient But Still Have Normal Levels Of Calcium?

According to one of my doctors, my Vitamin D level was "less than 1." I asked what the implications of such a low Vitamin D level are and he explained how vitamin D is essential to facilitate the absorption of calcium to prevent osteoporosis. My calcium level has always been well within normal limits; my thyroid and PTH levels have been normal; my DEXA was above normal indicating super strong bones.

I actually have several questions: How can my vitamin D be so low? Could this be a false reading? What happens when the Vit D is raised to where it should be? Will my calcium then be too high? What are the implications of hypercalcemia?

I have difficulty understanding how my Vitamin D could possibly be so low since I spend considerable time in the sun (often without sunscreen), eat vitamin D fortified cereals with fortified milk every weekday and have no evidence of hypocalcemia. Then again, I also endure symptoms of Vit D deficiency including bone pain and muscle weakness.

I look forward to any insight you can provide. Thanks!!

Answer

Your question about whether or not your seemingly normal calcium level will wind up too high if you start supplementing with vitamin D, is a good one, MERF. (Not everyone is aware of the important relationship between vitamin D and calcium to our bodies, so you are way ahead of the game! )

But, the relationship is not as simple as it may seem...

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!

Be well-

Hope