Oral NR was well tolerated with no adverse events. Significant increases comparing baseline to mean concentrations at steady state (Cave,ss) were observed for both NR (p = 0.03) and NAD+ (p = 0.001); the latter increased by 100%. Absolute changes from baseline to Day 9 in NR and NAD+ levels correlated highly (R2 = 0.72, p = 0.008)...An NR dose of 1000 mg twice daily significantly increased steady-state, whole-blood levels of NAD+ in all study participants with individual increases ranging from 35–168% above baseline NAD+ levels...Participants reported none of the serious side effects seen with similar doses of niacin, such as flushing, pruritus, hyperglycemia, hyperuricemia, or elevations in liver or muscle enzymes...Because NR increases circulating NAD+ in humans, NR may have potential as a therapy in patients with mitochondrial dysfunction due to genetic and/or acquired diseases.