Vitamin D status in kidney transplant patients: need for intensified routine supplementation

BACKGROUND: A high prevalence of vitamin D insufficiency has been found in the general population and in patients with chronic kidney disease. OBJECTIVE: The aim was to examine vitamin D status and determinants and metabolic correlates of serum 25-hydroxyvitamin D in a population of adult Danish kidney transplant patients. DESIGN: This was a cross-sectional study of 173 adult kidney transplant patients with a mean (+/-SD) age of 53.4 +/- 11.7 y and a median graft age of 7.4 y (interquartile range: 3.3-12.7 y). Serum concentrations of intact parathyroid hormone (S-PTH), 25-hydroxyvitamin D [S-25(OH)D], and 1,25-dihydroxyvitamin D [S-1,25(OH)(2)D] were measured. Dietary and supplementary intake of vitamin D, avoidance of solar ultraviolet B exposure, and selected lifestyle factors were assessed in a subgroup (n = 97). RESULTS: Fifty-one percent of the patients had vitamin D insufficiency [S-25(OH)D 40-75 nmol/L], and an additional 29% had moderate-to-severe vitamin D deficiency [S-25(OH)D < or = 39 nmol/L]. In multiple regression analysis, sun avoidance (negative association) and vitamin D supplementation (positive association) were independent determinants of S-25(OH)D concentrations. Low S-25(OH)D concentrations were associated with 1) increased S-PTH concentrations (P = 0.0002), independently of S-1,25(OH)(2)D concentrations, and 2) decreased S-1,25(OH)(2)D concentrations (P = 0.002), independently of graft function. CONCLUSIONS: Hypovitaminosis D is common among Danish kidney transplant patients and is associated with reduced concentrations of S-1,25(OH)(2)D and increased S-PTH concentrations. Sun avoidance and vitamin D supplementation are important determinants of vitamin D status. The observed hypovitaminosis D might be corrected by intensified routine vitamin D supplementation as opposed to the current supplementation practice.