Vitamin D insufficiency, defined as serum 25-hydroxyvitamin (OH) D level less than 30 ng/ml, is highly prevalent not only in the general population but also in chronic kidney disease (CKD) population. Many guidelines including the National Kidney Foundation-Kidney Disease Outcomes Quality Initiative (NKF-KDOQI) have consistently recommended vitamin D supplementation in patients with pre-dialysis CKD with vitamin D insufficiency with ergocalciferol or cholecalciferol to achieve 25(OH)D level of more than 30 ng/ml using serum levels-based titration regimen. However, this protocol has not been studied in end stage kidney disease patients treated with maintenance dialysis.

The investigators plan to conduct a randomized study comparing the two different protocols between serum 25(OH)D level-based titration regimen and fixed dose of ergocalciferol supplementation among dialysis patients for a total period of 6 months. At the study completion, investigators also plan to compare the proportion of participants achieving serum 25(OH)D of more than 30 ng/ml, CKD-related metabolic and bone parameters as well as non-skeletal effect of vitamin D supplementation for each group.

Inclusion Criteria:

• age > 18 years
• on maintenance dialysis (hemodialysis or peritoneal dialysis) > 3 months
• 25(OH)D < 30 ng/ml
• able to provide inform consent form

Exclusion Criteria:

• current ergocalciferol or cholecalciferol treatment
• known allergy to ergocalciferol
• active inflammation or infection
• advanced stage of cancer
• pregnancy
• lactation
• on immunosuppressive drugs or corticosteroids