Explaining Vitamin D Levels & Other Metabolic Issues
1) Vitamin D is a chemical that helps the body absorb calcium from food. Vitamin D is mostly made by our skin when we are exposed to sunlight. However, the body also absorbs some Vitamin D from the food we eat.
2) Whether Vitamin D comes from food or sunlight, it must be converted to an active form in the kidneys. An enzyme called 1α-hydroxylase is produced in the kidney and converts Vitamin D to the active form.
3) If you have decreased kidney function the kidney will not produce enough 1α-hydroxylase, which results in Vitamin D deficiency. This usually occurs when GFR is less than 40mL/min, but can happen above a GFR of 40mL/min as well.
4) If the Vitamin D level falls too low, the body cannot absorb calcium from the food we eat.
5) When the calcium level falls too low, the body produces Parathyroid Hormone (also known as PTH). PTH tries to keep the calcium level in the blood normal by increasing calcium absorption from food (which can only happen if you have enough vitamin D), but also takes calcium out of the bones. Overtime, this can lead to weak bones which results in osteoporosis and fractures. Additionally, the Parathyroid Glands, which produces PTH, can eventually work so hard that the Parathyroid Glands go out of control and make too much PTH. This can cause persistently high calcium levels.
Besides calcium, the other mineral that can be effected by decreased kidney function is phosphorous (also known as phosphate). The kidney excretes excess phosphorous. If the kidney function is decreased, it cannot excrete enough phosphorous, which results in high levels of phosphorous. Phosphate comes from diet, primarily diary products, nuts, and meat. Phosphate and calcium together make up most of our bones. Uncontrolled high phosphate levels cause calcification (hardening) of joints, vessels, and soft tissue when the calcium phosphorous product is too high (the calcium phosphorous product is the calcium level multiplied by the phosphorous level).
Other long-term complications of kidney disease is anemia. Anemia typically starts to develop when GFR drops below 50mL/min. The worse the kidney function becomes, the worse the anemia becomes. Anemia develops because the kidney produces erythropoietin. Erythropoietin is needed for development of Red Blood Cells. Anemia is monitored by checking hemoglobin and hematocrit.
Always check with your physician prior to starting any supplements or over-the-counter products.
Hamilton CW, ed. Renal Failure: Chronic. In: Wells BG, DiPiro JT, Schwinghammer TL, and Hamilton CW. Pharmacotherapy Handbook. 5th Ediction. New York, NY: McGraw Hill; 2003:802-812.
National Kidney Foundation. K/DOQI Clinical Practice Guidelines for Bone Metabolism and Disease in Chronic Kidney Disease.Am J Kidney Dis 42:S1-S202, 2003 (suppl 3).
-Karen Curzio, PharmD (a Medical Professional that is very supportive and also trying to help us in the research!)