Validation of NAD+ Measurements for Human Clinical Studies

* Male or female age18-35 years or 70 years or older, healthy * if female reproductive potential, use of highly effective contraception (at least 1 month prior to screening and during study participation). * No known sensitivity to NR * No use of niacin, blood thinners or chemotherapy agents * HbA1c below 8.5% and not diabetec requiring insulin. * Not using/taking corticosteroids * No laboratory abnormalities indicating significant anemia, bleeding risk, kidney disease, or liver disease * No contraindication to MRI * Not Pregnant, lactating, or planning to become pregnant during participation * Not taking multivitamins or any over-the-counter supplements except calcium and vitamin D (any other supplements - discontinued 2 weeks prior to study participation). * not taking/ undergoing another investigational drug or other intervention within the past 30 days.