Association between serum vitamin D level and inflammatory markers in non-obese patients with type 2 diabetes

Objective To investigate the association between serum 25(OH)D3 and high sensitive C-reactive protein (hs-CRP), tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6) inflammatory markers in non-obese patients with type 2 diabetes mellitus (T2DM). Methods From June 2015 to September 2015, in this cross-sectional study, 120 non-obese patients with T2DM(female in 58 cases, male in 62 cases) in Taiyuan Central Hospital were selected as T2DM group, and 120 non-obese patients with T2DM and 96 healthy subjects(control group) were recruited.The serum concentrations of glucose, HbA1c, insulin, 25(OH)D3 and inflammatory markers including TNF-α, IL-6 and hs-CRP were measured.A homeostatic model of insulin resistance (HOMA-IR) was also evaluated.The clinical and biochemical characteristics of T2DM were observed in the group of vitamin D deficiency group, vitamin D insufficiency group and vitamin D normal group.And the relativities were analyzed between it with hs-CRP, TNF-α, IL-6, HOMA-IR, INF, FBG, BMI, WHR, and so on.The relativities were observed between 25(OH)D3 with all the factors. Results The mean serum concentration of 25(OH)D3 in the non-obese T2DM group was (10.65±3.55)ng/mL, which was significantly lower than (18.44±5.21)ng/mL in the normal control group (t=-6.84, P=0.012). The levels of serum TNF-α and IL-6 in the T2DM group were (15.51±4.87)ng/L and (18.12±4.13)ng/L, respectively, which were significantly higher than those in the control group [(8.99±2.54)ng/L, (8.89±2.07)ng/L](t=7.95, 10.04, P=0.017, 0.007). The proportions of deficiency, insufficiency and normal of vitamin D in T2DM patients were 60.83%, 31.67%and 7.50%, respectively .The levels of TNF-α and IL-6 in the serum 25(OH)D3 deficiency group were significantly higher than those in the normal 25(OH)D3 group [(17.93±4.94)ng/L vs.(10.30±4.52)ng/L, F=6.897, P=0.026; (20.14±4.99)ng/L vs.(16.39±5.06)ng/L, F=10.589, P=0.017]. There was a significant correlation between serum 25(OH)D3 and HOMA-IR(r=-0.041; P=0.030), TNF-α(r=-0.229; P=0.040) and IL-6 levels (r=-0.299; P=0.032), but there was no significant correlation with inflammatory factor hs-CRP and fasting blood glucose. Conclusion Vitamin D deficiency is common in patients with T2DM, and systemic chronic inflammation may also play an important role in the pathogenesis of T2DM.This study shows that vitamin D may play an important role in the pathogenesis of insulin resistance and chronic systemic inflammatory response, an important pathogenesis of T2DM. Key words: Diabetes mellitus, type 2; Vitamin D; Blood glucose; Tumor necrosis factor-alpha; Interleukin-6; C-reactive protrin; Body mass index