People with reduced kidney function (chronic kidney disease; CKD) develop changes in circulating blood levels of calcium and phosphorus. The kidney gradually loses the ability to remove phosphorus from the blood and cannot activate adequate amounts of vitamin D, to maintain normal levels of calcium. The parathyroid gland senses these changes and compensates to increase calcium by elevating production and release of parathyroid hormone. These metabolic changes alter bone metabolism to release calcium and accordingly lead to bone abnormalities including altered bone production. Consequently bone deformation, bone pain, and altered risks of fracture may occur.
Treatment for these mineral changes in CKD include replacing activated vitamin D to suppress parathyroid hormone release. Earlier activated vitamin D preparations (calcitriol and alfacalcidol) were associated with increased circulating calcium and phosphorus levels through their direct action on the vitamin D receptor. Newer agents have since been developed that similarly suppress parathyroid hormone but may limit increases in calcium and phosphorus. Avoidance of increased calcium and phosphorus is considered important as these minerals may activate calcification in arteries and tissues, potentially leading to heart disease and tissue damage.
We identified 60 studies of vitamin D preparations in people with CKD and requiring dialysis involving 2773 people. No studies were designed to understand the effect of vitamin D therapy on risks of death. Vitamin D agents suppress PTH significantly compared with no treatment, however also increase both circulating calcium and phosphorus levels. Intravenous vitamin D may lower PTH more than oral vitamin D. Few studies directly compare newer vitamin D therapies with earlier (and presently more common treatment options; calcitriol and alfacalcidol); newer treatment options therefore cannot be recommended as superior to established treatments.
In the future, new studies will required to know if vitamin D effects on parathyroid function improve survival, bone pain, and need for parathyroid removal by surgery. It is possible that vitamin D compounds are beneficial to patients regardless of their effects on parathyroid hormone. This can only be adequately evaluated by conducting specific studies that are large enough to be sure of any treatment differences.