Vitamin D deficiency and mortality in patients receiving dialysis: the Comprehensive Dialysis Study

Objective: Although several studies have shown poorer survival among individuals with 25-hydroxy (OH) vitamin D deficiency, data on patients receiving dialysis are limited. Using data from the Comprehensive Dialysis Study (CDS), we tested the hypothesis that patients new to dialysis with low serum concentrations of 25-OH vitamin D would experience higher mortality and hospitalizations.

Design: The CDS is a prospective cohort study.We recruited participants from 56 dialysis units located throughout the United States.

Subjects and intervention: We obtained data on demographics, comorbidites, and laboratory values from the CDS Patient Questionnaire as well as the Medical Evidence Form (CMS form 2728). Participants provided baseline serum samples for 25-OH vitamin D measurements.

Main outcome measure: We ascertained time to death and first hospitalization as well as number of first-year hospitalizations via the U.S. Renal Data System standard analysis files. We used Cox proportional hazards to determine the association between 25-OH vitamin D tertiles and survival and hospitalization. For number of hospitalizations in the first year, we used negative binomial regression.

Results: The analytic cohort was composed of 256 patients with Patient Questionnaire data and 25-OH vitamin D concentrations. The mean age of participants was 62 (±14.0) years, and mean follow-up was 3.8 years. Patients with 25-OH vitamin D concentrations in the lowest tertile (<10.6 ng/mL) at the start of dialysis experienced higher mortality (adjusted hazard ratio 1.75, 95% confidence interval [CI] 1.03-2.97) as well as hospitalization (adjusted hazard ratio 1.76, 95% CI 1.24-2.49). Patients in the lower 2 tertiles (<15.5 ng/mL) experienced a higher rate of hospitalizations in the first year (incidence rate ratio 1.70 [95% CI 1.06-2.72] for middle tertile, 1.66 [95% CI 1.10-2.51] for lowest tertile).

Conclusion: We found a sizeable increase in mortality and hospitalization for patients on dialysis with severe 25-OH vitamin D deficiency.