Evaluation of Colecalciferol Substitution in Dialysis Patients

Inclusion Criteria: 1. Serum 25-OH-Vit.D-levels \< 60 ng/ml 2. Age \> 18 years 3. dialysis treatment \> 3 Months 4. signed written informed consent 5. Serum-Calcium-levels \< 2,6 mmol/l within the last 4 weeks 6. Serum-Phosphate-levels \< 7,0 mg/dl within the last 4 weeks 7. Ca x P-Product \< 75 mg2/dl2 within the last 4 weeks Exclusion Criteria: 1. Serum 25-OH-Vit.-D-levels \> 60 ng/ml 2. concommitant participation in another interventional trial 3. psychiatric disorders preventing from valid informed consent 4. Hyperphosphatemia (\> 7,0 mg/dl) within the last 4 weeks 5. Hypercalcemia (\> 2,6 mmol/l) within the last 4 weeks 6. Ca x P-Product \> 75 mg2/dl2 within the last 4 weeks 7. pregnancy or lactation 8. known malignancy 9. liver disease, defined as 2-fold upper limit of ASAT-, or ALAT-levels 10. PTH levels \< 50 pg/ml 11. current clinically relevant infections treated with antibiotic therapy and raised hsCRP levels 12. Chronic viral Infectious diseases (e.g. HIV, Hepatitis B or C) 13. Immunosuppressant Medication 14. known hematologic disorders, other than renal anemia 15. age below 18 years 16. known anaphylactic reaction against the study medication or other ingredients of the study drug preparation 17. renal calculus 18. Pseudohypoparathyroidism 19. Medication including cardiac glycosides 20. Sarkoidosis