More than 80% of older adults have hypertension, with a higher prevalence of high systolic blood pressure (SBP) putting them at high risk for cardiovascular (CV) disease and death. Because drug therapy that lowers SBP is associated with side effects such as hypotension, syncope, and kidney dysfunction, there is a great need for effective lifestyle SBP-lowering interventions for the older population that can replace drug therapy. While aerobic exercise is a recommended lifestyle intervention for controlling SBP and preventing CV disease naturally, in older adults it has been shown to be less effective in vascular-tissue remodeling because of arterial stiffness, resulting in less efficient SBP control. Reduced bioavailability of nicotinamide adenine dinucleotide (NAD+), a cofactor for the deacetylase sirtuin1 (SIRT1), may contribute to age-related vascular dysfunction via oxidative stress and reduced nitric oxide (NO). Exercise-induced overexpression of NAD+-dependent SIRT1 improves the bioavailability of NO. Preclinical evidence suggests that poor vascular function improvement in response to exercise in older mice is caused by insufficient NAD+ levels to stimulate SIRT1 activity. Importantly, replenishment of NAD+ levels induced vascular remodeling, improved vascular function, and reduced SBP in mice. An objective of this study, therefore, is to test a combination of aerobic exercise and nicotinamide riboside, a compound that replenishes NAD+ levels, to optimize exercise's SBP-lowering effect in hypertensive older adults. Initial human clinical trials demonstrated that nicotinamide riboside supplementation (1,000 mg/day) was safe and showed a higher potential to reduce SBP and arterial stiffness in participants with elevated SBP. As we have preclinical evidence that combining NAD+ replenishment with exercise is an ideal strategy for improving vascular function, our central hypothesis is that the intervention of aerobic-exercise training combined with nicotinamide riboside supplementation will reduce SBP in hypertensive older adults more effectively than will exercise alone. We will enroll 54 participants ≥ 55 years and older into either: (1) 1,000 mg/day of nicotinamide riboside plus 3 days/week of supervised, center-based walking exercise (n=18), or (2) the same exercise program combined with placebo (n=18), or (3) 1,000 mg/day of nicotinamide riboside alone (n=18). All participants will undergo daytime continuous SBP at baseline, 3 weeks, and 6 weeks, and arterial-stiffness measurements by pulse-wave velocity at baseline and at 6 weeks. Elevated SBP will be determined as daytime average equal to or above 130 mmHg, measured by the 24-hour blood-pressure device. To our knowledge, this study will be the first attempt to enhance exercise therapy with nicotinamide riboside in hypertensive older adults. We believe that nicotinamide riboside is "the missing piece of the puzzle" in improving vascular remodeling and SBP management in older adults. Preliminary evidence from this pilot study may support a full-scale Phase III clinical trial in hypertensive older adults. The ultimate goal of this line of research is to find adjuvant strategies to improve the exercise's SBP-lowering effects in older adults.