This is a randomized, double-blind pilot study of Nicotinamide Riboside (NR) in Pediatric-onset Ulcerative Colitis (UC).

The investigators hypothesize that NR will alleviate mitochondrial dysfunction and restore metabolic homeostasis in the intestinal epithelium in pediatric patients with UC.

The purpose of the study are:

1. To establish the feasibility of an Randomized Clinical Trial (RCT) investigating the effects of NR in pediatric patients with UC.
2. To evaluate the effects of Nicotinamide adenine dinucleotide (NAD)+ repletion on intestinal epithelial mitochondrial structure and function in human UC patients. The investigators hypothesize that daily NR supplementation will restore NAD+ levels, enhancing Peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC1α) activity and mitochondrial structure/function.

Inclusion Criteria:

• Pediatric patients (≤18yo);
• Diagnosis of mild to moderate ulcerative colitis as determined by Pediatric Ulcerative Colitis Activity Index (PUCAI) and endoscopic scoring (Mayo) at the time of colonoscopy;
• Although the investigators will target newly diagnosed patients (therefore, treatment naïve), patients with established disease will also be enrolled.

Exclusion Criteria:

• Patients with acute severe ulcerative colitis;
• Concurrent gastrointestinal infection (ie. Clostridium difficile, Cytomegalovirus, etc.);
• A diagnosis of Crohn's disease;
• Indeterminate colitis/IBD-U;
• In general, patients that have been treated with steroids or antibiotics in the past three months. Patients on Biologic medications may be enrolled if their dose has been stable for at least three months. Final determination of eligibility will be at the discretion of the treating investigator. After the initiation of the study, subjects may receive any medication to treat their disease as dictated by their care providers;
• Patients who have other chronic inflammatory/autoimmune disorders or prior malignancy;
• Pregnant women (All women of childbearing age will be required to use contraception at the time of inclusion).
• Patients with existing renal or hepatic dysfunction;
• Per standard of care guidance, subjects with platelets <50,000 do not undergo endoscopy and, therefore, are not eligible.

De-identified data and samples may be shared with the funding agent, other researchers or federal repositories in the future under and approved agreement.

6 months after publication of the results of the study. Date will be available for 1 year.

Prior to any sharing of any data, the research data/documents will be coded and all subject identifiers will be completely removed. Only the PI and co-investigators will have access to the coding. All others will have access to the completely deidentified data only.

A data use agreement will be obtained and finalized prior to any of the data leaving the institution, and prior to any access by outside entities.