Vitamin D status of chronic kidney disease patients living in a sunny country.

BACKGROUND: Vitamin D nutritional status has been poorly investigated in chronic kidney disease (CKD) patients, especially those inhabiting a subtropical area where the sunlight incidence is abundant all year.
OBJECTIVE: The purpose of this study was to evaluate the status of vitamin D and to analyze the relationship of circulating 25-hydroxyvitamin D [25(OH)D] with other serum parameters of mineral metabolism in patients with CKD not yet on dialysis.
DESIGN: This cross-sectional study enrolled 144 nondiabetic CKD patients not yet receiving dialysis (stages 2 to 5 of CKD). Fasting blood samples were obtained for measurements of 25-hydroxyvitamin D [25(OH)D], 1,25-dihydroxyvitamin D [1,25(OH)(2)D], intact parathyroid hormone, phosphorus, and calcium.
RESULTS: In the entire sample, the serum concentration of 25(OH) was 34.3 +/- 18.3 ng/mL (+/-SD unless otherwise noted). A deficiency of vitamin D, i.e., 25(OH)D <15 ng/mL, was found in only one patient. Fifty-seven patients (39.6%) were considered vitamin D-insufficient (16 to 30 ng/mL). The vitamin D-insufficient group contained more females, a higher degree of proteinuria, and a lower serum concentration of 1,25(OH)(2)D. In multiple regression analysis, 25(OH)D was associated positively with 1,25(OH)(2)D, serum calcium, and proteinuria, whereas 1,25(OH)(2)D was associated only with 25(OH)D and phosphorus. The variables associated with intact parathormone were serum phosphorus and creatinine clearance, but not 1,25(OH)(2)D or 25(OH)D.
CONCLUSION: Despite an elevated prevalence of vitamin D insufficiency, the serum concentration of 25(OH)D was, on average, higher than that found in patients inhabiting higher-latitude regions. This higher serum concentration may have contributed to the differences found in the relationship between vitamin D metabolites and other serum markers of mineral metabolism in our CKD patients.