An association between hypovitaminosis D and insulin resistance has been highlighted. Effects of vitamin D are not only mediated via the vitamin D receptors by active vitamin D metabolites, but 25(OH)D(3) also acts through VDR-independent pathways directly. It was reported that acute and chronic intravenous 1,25-dihydroxycholecalciferol therapy corrects insulin resistance in dialysis patients. There are no studies in patients on dialysis which evaluated relationship between 25(OH)D levels and insulin resistance. The aim of this study was to evaluate relationship between serum 25 (OH) D levels and insulin resistance in nondiabetic patients on peritoneal dialysis (PD).
We studied 53 nondiabetic patients on PD and in 25 age-, gender- and body mass index-matched healthy controls. Insulin resistance was evaluated by the homeostasis model assessment method (HOMA-IR) using fasting glucose and insulin levels. Vitamin D deficiency was defined if 25(OH)D(3) levels are equal to or less to 15 ng/ml.
Mean HOMA-IR index in patients on PD (3.1 ± 3.3) was significantly higher than those of controls (1.7 ± 1.9) (P < 0.05). The mean 25 (OH)D level in PD patients was (21.1 ± 19.0 ng/ml) lower than those of controls (27.5 ± 9.3 ng/ml) (P < 0.05). Twenty-five (47.2%) PD patients had vitamin D deficiency [mean 25(OH)D: 7.2 ± 3.2 ng/ml], and in 28 of them (52.8%) 25 (OH)D levels were more than 15 ng/ml (mean 33.5 ± 18.7 ng/ml). In PD patients with vitamin D deficiency, mean HOMA-IR index (4.2 ± 3.8) was significantly higher than that of PD patients whose 25 (OH)D levels were more than 15 ng/ml (2.2 ± 2.4) (P < 0.05). Twenty-one (84.0%) of PD patients with vitamin D deficiency, and 22 (78.6%) PD patients whose 25 (OH)D levels were more than 15 ng/mL have been receiving active vitamin D compounds for parathyroid hormone (PTH) control (P > 0.05). There was no significant difference between two PD groups according to mean duration of PD, age, gender, PTH, serum calcium, phosphorus, percentage of fat, and body mass index. There was a negative correlation between HOMA-IR index and 25 (OH)D levels in PD patients (r: -0,368, P < 0,05). In multiple regression analyses, the independent predictors of HOMA-IR index were 25(OH)D3 levels, duration of dialysis, and percentage of fat (measured by bioelectrical impedance) in PD patients.
Our findings show a negative correlation of 25(OH)D levels with insulin resistance in PD patients. PD patients with hypovitaminosis D are at higher risk of insulin resistance even if they are on treatment with active vitamin D for PTH control. Further studies are required to explore the relation between vitamin D deficiency and insulin resistance in PD patients.