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)₂D], 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)₂D. In multiple regression analysis, 25(OH)D was associated positively with 1,25(OH)₂D, serum calcium, and proteinuria, whereas 1,25(OH)₂D 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)₂D 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.