1). The metabolizing machinery for vitamin D has been characterized in multiple tissues, and the vitamin D receptor (VDR) identified in many, if not all human tissue types.6 Dobnig et al. first observed that baseline hypovitaminosis D increased risks of all-cause and cardiovascular mortality in a population referred for elective angiograms. Those patients in the lowest quartiles of serum 25-OHD had a cardiovascular event rate over

twice that of those in the highest quartile after multivariate adjustment.7 Similar findings have been reported by Wolf and Wang in the dialysis populations,8,9 and subsequently Inaguma and others have reported that lower 25-OHD and 1,25-OHD levels are associated Autophagy Compound Library solubility dmso with increased all-cause mortality in CKD stages 1–4 (summarized in Table 1).5,10,11 Further support for vitamin D’s pivotal role in mediating heightened Alectinib ic50 cardiovascular risk in CKD has been provided by several investigators reporting a survival benefit with the use of active vitamin D, summarized in Table 2.8,18–25 In a study by Teng et al. cardiovascular event rates were almost halved by the use of supplements (7.6 per 100 person years vs 14.6 per 100 person

years, P < 0.001).22 Obviously both selection and indication bias has to be acknowledged, and may limit these epidemiological cohort studies. While VDR activation was once considered only possible by renally produced 1,25-OHD (which is the case for cardiac myocytes), it is now clear that 1,25-OHD can be produced in an autocrine or paracrine fashion by extra-renal

1α-hydroxylase (CYP27B1) expressed in a variety of tissues, including vascular smooth muscle cells, skin, breast, prostate, colon and cellular components of the immune system.31 To date, while renal CYP27B1 activity diminishes with advancing CKD stage,32 there is no evidence to suggest that extra-renal enzymatic activity is reduced, adding support to the assertion that circulating levels of 25-OHD (the substrate for extra-renal CYP27B1) are of vital importance when assessing the vitamin D status of an individual, especially with CKD. This was emphasized by Edoxaban the work of Ravani, who identified that both 25- and 1,25-OHD were inversely related to the risk of both death and dialysis in unadjusted analyses.5 However, after using time-adjusted variables to account for deterioration in kidney function, 25-OHD remained a significant predictor of patient and renal survival, whereas 1,25-OHD did not, suggesting that 25-OHD is a better risk marker than 1,25-OHD in CKD.5 Insulin resistance is a highly prevalent cardiovascular risk factor in CKD, and all stages of the insulin resistant spectrum have been associated with 25-OHD deficiency.