This is a multicenter randomized, placebo-controlled trial of Vitamin D supplementation in patients on peritoneal dialysis to determine whether oral administration of vitamin D3 after curing an episode of peritonitis could reduce the risk of subsequent peritoneal dialysis-related peritonitis.

176 eligible patients on PD at one month after being cured from an episode of peritonitis will be enrolled and randomized into two groups, including the intervention group administered Cholecalciferol (produced by Xymogen Company) 4000 U (2 capsules) per day, and the control group administered placebo 2 capsules per day. All participants will be followed for 24 months, or till the occurrence of death, permanently transfer to hemodialysis, loss of follow-up, or withdrawal from the study, whichever comes first. The primary outcome is the occurrence of subsequent peritonitis. The study aims to identify whether oral administration of vitamin D3 after curing an episode of peritonitis could reduce the risk of subsequent peritoneal dialysis-related peritonitis.

Inclusion Criteria:

• Medically stable and receiving peritoneal dialysis for > 1 month
• Older than 18 years old
• Serum 25(OH)D < 30ng/ml
• Adequate dialysis on evaluation with weekly Kt/V ≥ 1.5, or (revised time: 2023-7-11) without clinical uremic symptoms

Exclusion Criteria:

• Receive Vitamin D2/D3 during the previous 1 month (revised time: 2023-7-11) ;
• History of allergic reaction to Cholecalciferol;
• Current or past malignant disease, active hepatitis or hepatic failure, active autoimmune disease, severe digestive malabsorption or an eating disorder, HIV/AIDS;
• Acute systemic infection, cardiovascular disease, surgery, or trauma in the last month;
• A high probability of receiving a kidney transplant or transferring to hemodialysis or drop-out due to socioeconomic causes within 6 months;
• History of kidney transplant;
• Hemodialysis combined with peritoneal dialysis currently;
• Pregnant or breastfeeding;
• Not suitable enrolled assessed by researchers, including patients who could not regular follow-up

Random number will be generated by statistician who is not involved in the study, and will be masked to all participants, caregivers, investigators and outcomes assessors. Only the drug dispensing personnel will have the decoding table. When an eligible patient is enrolled, he/she will be given a sequential patient number, according to block randomization. Such a patient number indicated its group allocation. The drug dispensing personnel will offer the corresponding drug, however with a random drug number. Serial Serum 25- hydroxy-Vitamin D levels, obtained every three months, will be declassified at the end of the study (24 months after enrollment), or till the occurrence of death, permanently transfer to hemodialysis, loss of follow-up, or withdrawal from the study, whichever comes first.