Relationship between serum 1,25-dihydroxyvitamin D and mortality in patients with pre-dialysis chronic kidney disease

Background It is known that vitamin D has many functions besides involvement in calcium metabolism. It has recently been recognized that vitamin D deficiency is associated with mortality, especially in cardiovascular disease (CVD). Vitamin D deficiency is common in end-stage renal disease, but develops from the early stage of chronic kidney disease (CKD). So we investigated whether the serum level of the activated form of vitamin D (1,25-dihydroxyvitamin D) affected mortality in patients with CKD stages 3 and 4. Methods Between January 1, 1995, and June 30, 2006 we measured serum 1,25-dihydroxyvitamin D In 226 patients with CKD stages 3 and 4 and classified the results into two groups depending on whether the level was below (group I) or above (group II) 20 pg/ml. We ended the follow-up period on December 31, 2006. We compared all-cause and cardiovascular mortality between the two groups. We also examined predictors of mortality by using Cox proportional regression analysis. Results Two-hundred and twenty-six patients (67 men and 159 women, mean age 67.0) were registered in this study, and groups 1 and 2 comprised 84 and 142 patients, respectively. During the follow-up period 43 patients died. CVD was the major cause of death, followed by infectious disease. The Kaplan-Meier survival curve revealed that all-cause mortality was significantly higher in group I, but a significant difference between CVD mortality in the two groups was not demonstrated. By Cox proportional regression analysis, group I was related to all-cause mortality, but this was not proved to be an independent predictor. Conclusion The results suggested that serum level of 1,25-dihydroxyvitamin D was associated with all-cause mortality in patients with CKD stages 3 and 4.