An update on vitamin D as related to nephrology practice: 2003.

In this article, an up-to-date consideration of vitamin D therapeutics in nephrology is reviewed. The condition of vitamin D insufficiency is defined as the level of serum 25(OH)vitamin D at which vitamin D2 or D3 supplementation leads to a reduction of levels of parathyroid hormone (PTH). The risks of such vitamin D insufficiency in the normal population and likely risks in individuals with chronic kidney disease (CKD) stages 3 and 4 are reviewed. The potential for its safe treatment and prevention using moderate supplements of vitamin D2 or vitamin D3 are outlined. The role of altered "vitamin D nutrition" in leading to the observed greater incidence of secondary hyperparathyroidism in African Americans with ESRD compared to other racial groups is considered. The actions of active vitamin D sterols to augment intestinal absorption of both calcium and phosphorus, the effect to reduce levels of PTH, and to be a factor contributing to the rising incidence of low bone turnover (adynamic bone) are discussed. Growing evidence for contributions of elevated levels of serum calcium, serum phosphorus, and the calcium x phosphorus product as factors contributing to vascular and cardiac calcification in ESRD patients are cited. Questions are raised about whether the current practice of vitamin D usage in ESRD patients might be a contributing factor to such vascular abnormalities. The economic factors that likely affect the usage of intravenous vitamin D sterols in the United States are reviewed. It is recommended that potential adverse vascular effects of vitamin D sterols related to the increments of serum Ca and P be carefully evaluated.