Vitamin D Deficiency In Chronic Kidney Disease

Vitamin D is synthesized in the skin under direct sunlight; it occurs naturally as vitamin D3. Vitamin D is chiefly absorbed from food sources that contain vitamin D such as eggs, fish and cod liver oil. Initially, vitamin D is inactive and has to be processed into an active form. The kidneys are involved in the activation vitamin D; they convert hydroxyvitamin D from the liver to active vitamin D.

Chronic Kidney Disease

The kidneys are responsible for filtering metabolic wastes and removing excess fluid from the blood. Failure in this task leads to a buildup of metabolic wastes in the body, which can ultimately lead to death. The kidneys are also the final step in the activation of vitamin D. They convert hydroxyvitamin D from the liver to active vitamin D, which helps in the absorption of calcium in the gut. In chronic kidney disease, the kidneys gradually loose the ability to filter the blood and eventually the ability to activate vitamin D. Failure to activate vitamin D leads to low active vitamin D in the blood.

Complications

Chronic kidney disease prevents the activation of vitamin D; low active vitamin D in the blood leads to low blood calcium. In chronic kidney disease, there is an increased release of parathyroid hormone. Parathyroid hormone is released from the parathyroid gland and it causes the breakdown of bone, thereby releasing calcium from bone into the blood. Excessive release of parathyroid hormone leads to weakening of bone, thereby increasing the likelihood of fracture. Low blood calcium can also cause an irregular pulse; in severe cases, it can lead to irreversible heart failure.

Associated Symptoms

A very low blood calcium weakens the heart muscle. A weak heart causes shortness of breath while lying down; it also causes leg and belly swelling. Low blood calcium leads to tetany, which is a condition of uncontrollable muscle contractions. Tetany may cause strange sensations over the tongue and lips. Calcium is needed to strengthen bone; low blood calcium leads to weakening of bone. Excess parathyroid hormone release as a result of low blood calcium worsens an already weak bone. Bone and joint pain are major complaints when parathyroid hormone is in excess. Generalized weakness, abdominal pain and nausea can occur.

Diagnosis

A blood test is needed to diagnose vitamin D deficiency. The blood is tested for active vitamin D. A normal level of active vitamin D in the blood should be greater than 30 nanograms per milliliter, or ng/mL; if less than 30 ng/mL, it is abnormal or below normal. An active vitamin D level below 20 ng/mL is defined as vitamin D deficiency.

Management

Chronic kidney disease should be primarily addressed to avoid a build up of metabolic wastes in the blood. Vitamin D must be supplemented as well to prevent decrease in bone density and weakening of bone. The U.S. Department of Health and Human Services recommends the use of vitamin D at doses of 700 to 800 international units, or IUs, with 500 to 1,200 mg of calcium; this combination is effective in strengthening bone. Changes to diet should include increasing the intake of fish, eggs, vitamin D-fortified milk and cod liver oil; they are abundant sources of vitamin D.