Vitamin D status and clinical outcomes in incident dialysis patients: results from the NECOSAD study

Background. The majority of dialysis patients suffer from vitamin D deficiency, which might contribute to an adverse health outcome. We aimed to elucidate whether European dialysis patients with low 25-hydroxyvitamin D (25(OH) D) levels are at increased risk of mortality and specific fatal events. Methods. This was a prospective cohort study of incident dialysis patients in the Netherlands (the NECOSAD). We selected all patients with measured 25(OH) D at 12 months after the start of dialysis, the baseline for our study. By Cox regression analyses, we assessed the impact of 25 (OH) D levels on short-term (6 months of follow-up) as well as longer-term mortality (3 years of follow-up). Associations of 25(OH) D levels with cardiovascular and non-cardiovascular mortality were also determined. Results. The data from 762 patients (39% females, age 59 +/- 15 years, 25(OH) D = 18 +/- 11 ng/mL) were available. Fifty-one and 213 patients died during a follow-up of 6 months and 3 years, respectively. After adjustments for possible confounders, the hazard ratio (HR) (with 95% CI) for mortality was 2.0 (1.0-3.8) for short-term and 1.5 (1.0-2.1) for longer-term mortality when comparing patients with 25(OH) D levels <= 10 ng/mL with those presenting with 25(OH) D levels >10 ng/mL. Adjusted HRs for cardiovascular mortality were 2.7 (1.1-6.5) and 1.7 (1.1-2.7) for short- and longer-term mortality, respectively. For non-cardiovascular mortality, we observed no relevant association overall. The impact of 25(OH) D levels on clinical events was modified by parathyroid hormone (PTH) status, with low 25(OH) D levels meaningfully affecting outcomes only in patients with PTH levels above the median of 123 pmol/L. Conclusions. Vitamin D deficiency in dialysis patients is associated with an adverse health outcome, in particular with short- term cardiovascular mortality. Intervention studies are urgently needed to evaluate whether vitamin D supplementation improves health outcomes of dialysis patients.