Vitamin D And Kidney Damage

According to the Centers for Disease Control and Prevention, as of 2009, there are at least 4.5 million American adults with some form of kidney disease. The kidneys have several responsibilities, including the production of the active form of vitamin D. If the kidneys suffer enough damage, this job cannot be done, and the result may be weak and brittle bones.

Functions of the Kidneys

The kidneys have many functions. They have the responsibility to remove waste products from the bloodstream, so toxic substances do not build up. They secrete renin, a hormone, to increase blood pressure and another hormone called erythropoietin to stimulate the production of red blood cells. The kidneys reabsorb glucose, amino acids and plasma proteins. They maintain the proper amount of acids and bases in the bloodstream. The kidneys also produce the active form of vitamin D, as explained by Elizabeth Corwin, Ph.D. in "Handbook of Pathophysiology."

Production of Vitamin D

When there are low levels of calcium in the bloodstream, the parathyroid gland releases the parathyroid hormone. At first, people have an inactive form of vitamin D from their diet or when it is made after sunlight shines on their skin. Elizabeth Corwin, Ph.D., writes how the parathyroid hormone will then stimulate the kidneys and liver to change the inactive form to the active form of vitamin D. Scientists call this active form 1,25-dihydroxyvitamin D3, and this form of the vitamin will stimulate the small intestines to absorb calcium, to increase the calcium levels in the bloodstream.

Kidney Damage

There are many disorders that can damage the kidneys, says Suzanne Watnick, M.D., in "Current Medical Diagnosis & Treatment." If the kidneys do not receive enough blood flow, they will not have enough oxygen to function, and this can lead to damage. If the urine flow from the kidneys is blocked, this can cause damage. Toxins, certain medications, specific diseases and cysts can all damage the kidneys, as well as bacterial, viral and fungal infections.

Effect of Kidney Damage on Vitamin D

Depending upon the amount of damage, the kidneys may not respond to the parathyroid hormone and make the active form of vitamin D. In that case, the blood calcium levels stay low. The consequences are explained by Larry Johnson, M.D., Ph.D., in "The Merck Manual for Healthcare Professionals." The parathyroid gland continues to release the parathyroid hormone, which results in a disorder called hyperparathyroidism. Trying to increase the calcium levels, the calcium comes from the bones. The kidneys excrete phosphate, and with the bones now losing calcium and phosphate, they become weak and brittle.

Evaluation

People with kidney problems may not have any specific symptoms or they may not have any symptoms at all until the kidney damage is severe, according to Seyed-Ali Sadjadi, M.D., of Loma Linda University School of Medicine. The evaluation includes any history of symptoms, a physical exam, complete blood count, blood chemistry levels and possibly ultrasound, CT or magnetic resonance imaging tests. A blood test can also determine the calcium and phosphate levels.