Absorption and Tolerability of Injectable Administration of Niagen®+, as Compared to NAD+

Inclusion Criteria:

* Provision of signed and dated informed consent form
* Stated willingness and demonstrated ability to comply with all study procedures, as well as availability for the duration of the study
* Lives within 100 miles of the NRI study site
* Any gender, aged 40-65, inclusive
* Good general health as evidenced by medical history
* BMI 25-34.9 kg/m2
* Sedentary behavior (defined as \<20 minutes per day or 100 minutes per week of moderate to vigorous exercise)
* Demonstrated fatigue (Fatigue Assessment Scale) defined as a below-average score
* For females of reproductive potential: use of highly effective contraception for at least 1 month prior to screening and agreement to use such a method during study participation and for an additional month after the end of the study
* Agreement to adhere to Lifestyle Considerations throughout study duration

Exclusion Criteria:

* Current diagnosis of any seizure disorder, diabetes or insulin resistance, any kidney or liver disorder, heart disease, anemia, cancer, or Parkinson's disease
* ANY chronic illness (pre-disease state acceptable)
* Out of range phosphate levels at baseline
* BMI less than 25 or greater than or equal to 35
* Pregnancy, trying to conceive, or breastfeeding
* Known allergic reactions to any components of the intervention or related compounds, including any form of B3
* Positive COVID-19 test within 30 days of the study period
* Recent dramatic weight changes (10% change in body weight in the last 6 months)
* Existing usage of a NAD+ or NAD precursor supplement in any form (oral, nasal, patch, or injection/IV administration), including a B-complex supplement, within 60 days of the study, not including multivitamins.
* Introducing a new medication, supplement, investigational drug, or other intervention (including lifestyle changes) within 60 days of the start of the study.