NAD Supplementation in Parkinson's Disease

The goal of this clinical trial is to learn whether Nicotinamide Riboside, a form of Vitamin B3 also known as NR, can improve blood vessel health in the brain, memory, and physical function in eligible study participants. NR is considered investigational for this study because it is not yet established for this specific use. The main questions it aims to answer are: Can NR improve non-invasive measures of blood vessel health in the brain? Can NR improve memory testing results and physical function? Researchers will compare participants who receive NR with participants who receive a placebo, an inactive substance that looks like the study drug, to see if NR has beneficial effects. Participants will be randomly assigned to receive either NR or placebo. They will complete 3 study visits over 13 weeks at the Translational Geroscience Laboratory at the University of Oklahoma Health Campus. During the visits, participants will complete questionnaires, memory testing, non-invasive blood vessel measurements, physical function tests, and a blood draw.

Inclusion Criteria: * Clinical diagnosis of Parkinson's disease according to Movement Disorder Society clinical diagnostic criteria (59), Hoehn and Yahr stages I-III at enrollment (ON medication state when applicable) (60). * Age ≥55 years at enrollment. * Adequate hearing and visual acuity to participate in the examinations * Ability to provide written informed consent in English. * Ability to complete study procedures, including seated tasks and walking tasks (with or without an assistive device, if needed for safety). * Stable antiparkinsonian medication regimen for ≥4 weeks prior to baseline (or drug-naive). Exclusion Criteria: * Not able to communicate or follow instructions due to aphasia or severe cognitive impairment. * Active CNS disease including multiple sclerosis, uncontrolled seizures, active cancer. * Cerebrovascular accident other than TIA within 60 days prior to Visit 0. * Major psychiatric disease, including major depression not currently controlled on medications, alcohol or drug abuse. * Abnormal kidney function (creatinine \>2mg/dL or EGFR \