Background

Cardiovascular (CV) events are common in patients with chronic kidney disease (CKD) but inadequately explained by traditional risk factors. Vitamin D deficiency is highly prevalent in CKD and has been proposed to be a non-traditional risk factor, but its relationship with vascular function is unknown.

Methods and results

The aim of this study was to investigate the relationship between vitamin D levels and endothelial function in non-diabetes patients with mild to moderate CKD. Endothelial function was measured non-invasively using brachial artery flow mediated dilation (FMD). 25 hydroxy vitamin D levels were measured using electrochemiluminescence immunoassay.

In 50 CKD patients (age 56 ± 11 years, BMI 25 ± 4 kg/m², 46% females, 14% smokers, 86% hypertensives, 52% with dyslipidaemia) the mean vitamin D level was 53 ± 33 nmol/L (21 ± 13 ng/L). The mean FMD was 3.8 ± 2.4%. Decreasing 25 hydroxy vitamin D levels were associated with decreasing FMD [r = 0.44, p = 0.001]. In multivariate analysis the association remained independent after adjustment with traditional risk factors (adjusted beta 0.451; t = 3.46; p < 0.002).

Patients with low vitamin D (≤37.5 nmol/L) demonstrated low FMD compared to patients with vitamin D values >37.5 nmol/L (4.4 ± 2.5% vs. 2.5 ± 1.6%; p = 0.007); however the traditional risk factors were similar between the two groups.

Conclusion

This is the first demonstration of an association of vitamin D deficiency with abnormal vascular endothelial function in non-dialysis CKD patients. Further studies with intervention and exploration of the mechanism are needed to establish a cause effect relationship.