【Abstract】Objectives To evaluate the relationship between serum 25(OH)D level and the changes of serum soluble α-Klotho and aortic arch calcification in hemodialysis (HD) patients. Methods This was a crosssectional study enrolled in 152 HD patients from the Dialysis Center of Beijing Friendship Hospital. Fasting blood samples were collected prior to hemodialysis at the second hemodialysis session in a week. Serum 25(OH)D and intact parathyroid hormone (iPTH) were assayed by an automatic electrochemiluminescence immunoassay instrument. Serum α-Klotho was determined using a sandwich enzyme-linked immunosorbent assay (ELISA) kit. Posterior-anterior chest X-ray examination was used to assess aortic arch calcification. Results The average serum 25(OH)D level was 19.97±8.30 ng/ml in the HD patients, in which vitamin D deficiency was found in 106 patients (69.7%). The average serum α-Klotho level was 421.69±185.28 pg/ml. Aortic arch calcification was found in 89 patients (58.6%). In patients with vitamin D deficiency, females were more than males (54.7% vs. 28.3%, c2=9.660, P= 0.006); serum α-Klotho levels were lower (399.16±179.62 pg/ml vs. 473.61±189.62 pg/ml, t=-2.308, P=0.022); and the prevalence of aortic arch calcification was higher but without statistical significance (63.2% vs. 47.8%, c2=3.127, P=0.077). Linear stepwise regression analysis showed that serum 25(OH)D level was independently correlated with serum α-Klotho level (P=0.022). Binary logistic regression analysis confirmed that age (OR=1.115, 95% CI=1.069- 1.163, P＜0.001) and serum 25

(OH)D (OR=0.948, 95% CI=0.901-0.998, P=0.041) were the independent risk factors for aortic arch calcification. Conclusions Vitamin D deficiency was prevalent in HD patients. Serum 25(OH)D was the independent risk factor for both circulating α- Klotho and aortic arch calcification. Therefore, serum 25(OH)D assay for HD patients is clinically valuable.