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Vitamin D and CKD
EasyLink Access #: 460
By Nadiya Lakhani, RD, LD
It’s seems that everyone is talking about vitamin D and for a good reason. Long winter months indoors and use of heavy sunscreen are some of the reasons that keep our bodies from absorbing the UV rays necessary to make healthy amounts of vitamin D leading to vitamin D deficiency. But for people with chronic kidney disease, it’s not just an issue of vitamin D deficiency but a deficiency in active vitamin D as well. Where Does Vitamin D come from and what does it do? Vitamin D is naturally found in food and is made in the body with the help of sunlight. In addition to sun, foods (fish, egg yolks, and milk) and dietary supplements are other sources of vitamin D. However to work in the body, vitamin D must be activated by the kidneys. It first goes through the liver and then the final stage of activation is completed by the kidneys. Next, this active vitamin D hormone works as a messenger telling the kidneys, bones, and intestines to balance calcium and phosphorus in the blood. Keeping calcium and phosphorus at the right balance is important to keep bones healthy and strong and to keep nerves and muscles working properly. When there is not enough active Vitamin D, the calcium in the body is not absorbed appropriately and bones get weak and brittle. What is Parathyroid Hormone (PTH)? PTH is another messenger needed for calcium and phosphorus balance. PTH is released by the parathyroid glands when 1) active vitamin D levels are too low or 2) when calcium levels are too low or 3) when phosphorus levels are too high. These glands continue releasing PTH until these levels are normal. PTH works by telling the kidneys to filter out extra phosphorus and to activate vitamin D. PTH also works on the bones to add calcium into the blood. What Happens in Chronic Kidney Disease (CKD)? As kidney function declines, the kidneys don’t respond to PTH and they are less able to balance calcium and phosphorus or activate vitamin D. Low calcium, high phosphorus, and low active vitamin D levels trigger the parathyroid gland to work “overtime” and continue releasing PTH in the blood. As the parathyroid gland continues to work overtime, this leads to too much PTH or a condition known as Secondary Hyperparathyroidism (SHPT). SHPT can be harmful to the body and if not treated early can lead to bone pain, nerve problems, itching, weak or brittle bones, calcium build up, and resistance to therapy. SHPT begins early in chronic kidney disease – well before dialysis is needed. So ask your physician about checking your PTH levels. Research shows that calcium and phosphorus levels are normal in CKD but this is only at the expense of PTH. PTH levels should be checked every three months and more frequently as kidney disease progresses. How Should SHPT Be Managed? During the early stages of CKD, the nephrologist may check Vitamin D levels, known as “25-hydroxy” as well as PTH levels and prescribe a vitamin D supplement, such as ergocalciferol or cholecalciferol. This is not active vitamin D. The body still needs to convert it to its active form in order to work properly. The nephrologist may then prescribe active vitamin D, such as Zemplar (Paricalcitol), Hectorol (doxercalciferol) or a branded generic known as Rocaltrol (calcitriol). These medications work to control the buildup of PTH. These are different from ergocalciferol or cholecalciferol (or from over the counter supplements you get at GNC) because they are not active and do not correct active vitamin D deficiency. Zemplar, Hectorol, and Rocaltrol all activate the vitamin D receptor but all have different side effects or impact on minerals such as calcium and phosphorus. Talk to your doctor about which one is best for you. In addition to following your treatment regime, it’s also important to follow your diet and know your numbers. You play the most important role in managing your SHPT and preventing bone disease. If you are not yet on dialysis, ask your doctor about medical nutrition therapy or RD counseling. A Registered Dietitian (RD) can talk to you about ways to slow down the progression of kidney disease and manage your SHPT.
About the Author
Nadiya Lakhani, works for Dallas Nephrology Associates as the Pre-Transplant dietitian along with seeing patients with CKD in office practice. Nadiya's background includes working as a Renal Dietitian for Fresenius Medical Care and as Clinical Dietition for various hospitals. She is also active within the renal community and serves as the Regional Representative for the National Kidney Foundation, Council for Renal Nutrition and American Dietetic Association, Renal Practice Group.
Last Updated October 2009
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