Vitamin D Deficiency & Elevated Alkaline Phosphatase
By M. Gideon Hoyle
, last updated March 19, 2012
Alkaline phosphatase, or ALP, is a specialized type of protein, called an enzyme, produced throughout your body. The specific chemical structure of this enzyme varies according to the type of tissue in which it resides. If you develop any one of a number of health disorders, your ALP levels can increase. Vitamin D deficiency is one potential cause of ALP elevation.
Because your body contains many types of ALP, it is classified as an isoenzyme, a term that describes enzymes that produce the same chemical reactions despite variations in their structure. ALP isoenzymes in your body support your basic function by triggering chemical reactions that cleave, or remove, a substance called phosphate from larger molecules and free that phosphate for use in other reactions. Areas of your body with particularly high amounts of ALP include your bones, liver and structures associated with your liver and gallbladder called bile ducts.
There are two types of ALP testing. If your doctor knows or suspects that you have a specific ailment, such as liver or bone disease, he will typically perform a blood test that calculates your total ALP. Normal findings on this test range from 44 to 147 IU/L. If your doctor doesn’t know if you have a specific disease, he can perform an ALP isoenzyme blood test, which can differentiate liver ALP from bone ALP. He can also use an ALP enzyme test to detect elevations associated with a vitamin D deficiency. Under normal circumstances, ALP isoenzyme blood levels in adults range between 20 and 140 IU/L.
ALP and Vitamin D
If you have a vitamin D deficiency, you can develop a condition called secondary hyperparathyroidism, which gets its name from the parathyroid glands located in your neck behind your thyroid gland. Along with the vitamin D in your body, a hormone from your parathyroid gland — called parathyroid hormone or PTH — helps regulate the levels and location of your internal supplies of the mineral calcium. Secondary hyperparathyroidism sets in when reductions in your vitamin D levels lead to reductions in your normal blood calcium levels. PTH in your blood offsets this calcium reduction by pulling abnormal amounts of calcium from your bones to your bloodstream. ALP isoenzyme testing does not directly uncover vitamin D deficiency. Instead, it is used to detect the presence of hyperparathyroidism.
ALP levels in developing bones are considerably higher than levels in fully grown bones, and normal ALP findings in growing children can range as high as 500 IU/L. Because of this natural variability in potential results, doctors don’t typically use ALP testing on children. Between the ages of 1 and 70, human beings need 600 IU of vitamin D per day. Infants need 400 IU per day, while older adults need 800 IU. Consult your doctor for more information on ALP elevation, ALP testing and vitamin D deficiency.