High-fat meal (HFM) consumption increases oxidative stress in humans. The metabolic cofactor nicotinamide adenine dinucleotide (NAD+), has been identified as a key regulator of oxidative stress. Older individuals suffer from low NAD+ levels and experience age-related increases in oxidative stress. Nicotinamide Riboside (NR), a newly discovered NAD+ precursor has demonstrated the ability to raise NAD+ in older adults. Nicotinic Acid (NA), another NAD+ precursor is established as one of the oldest anti-atherogenic supplements that improves vascular function. Similarities between NR and NA indicate NR may have potential vascular benefits yet to be discovered. We hypothesized that one week of NR supplementation would reduce postprandial oxidative stress and improve vascular function following consumption of a HFM (1050 kcal, 72g fat) in old and young participants. We performed a double-blind, placebo-controlled crossover study with 16 participants, divided into young (n=13) and old (n=3) groups, assessing one week of 250mg 2x/day NR on a lipid peroxidation indicator of oxidative stress. Microvascular function was determined with blood flow measurements of post occlusive reactive hyperemia (PORH), analyzed using laser speckle contrast imaging (LSCI). NR supplementation did not significantly affect levels of postprandial lipid peroxidation indicators of oxidative stress (MDA). No differences in postprandial PORH measures of microvascular function were identified for treatment, time and interaction. Plasma MDA, glucose, and triglycerides all increased postprandially with significantly higher levels reported in the old group compared to young (p<0.001, p=0.04, p<0.001, respectively). One week of NR supplementation was well tolerated in all participants but had no effect on postprandial oxidative stress and microvascular function.