# NAD+: The Coenzyme That Runs Cellular Energy Metabolism — A Research Field Guide > NAD+ is the redox coenzyme every cell uses to turn food into energy. Sold as a dietary supplement — usually as the precursors NMN and NR — with the heart, kidney, and muscle research summarized and cited. A literature digest of what the published research has shown — where blood levels reliably rise, where the organ data are strongest, and where the trail thins into the unproven. Every quantitative claim is cited. ## The short version NAD+ (a fuel-handling helper molecule every cell uses to turn food into usable energy) is not a drug. It is a coenzyme (a helper molecule an enzyme needs to do its job) made naturally inside every one of your cells, and its levels in tissue tend to fall as people age. Because the molecule itself is large and poorly absorbed when swallowed, most products marketed as "NAD+" are actually precursors (building blocks the body converts into NAD+) — chiefly NMN and NR. This site reads the published research: what the studies measured, in which species, at which doses. It is a digest, not advice, and nothing here is for sale. ## What the NAD+ literature has actually established NAD+ — nicotinamide adenine dinucleotide — is the central redox carrier (a molecule that shuttles electrons to release energy) of cellular metabolism, and a consumed fuel for the signaling enzymes that govern DNA repair, gene regulation, and inflammation [5]. Tissue NAD+ falls with age, and that decline is the rationale behind the whole precursor-supplement category [5]. The most reliable finding in the human literature is narrow and well-replicated: oral precursors raise blood NAD+ in a dose-dependent way. Nicotinamide riboside (NR) raised whole-blood NAD+ by 22%, 51%, and 142% at 100, 300, and 1000 mg/day over eight weeks in healthy overweight adults [4]. Oral NMN at 300-900 mg/day for 60 days raised blood NAD+ at days 30 and 60 across every dose group versus placebo in a multicenter, double-blind, randomized trial [3]. These are reproducible pharmacodynamic results — the [NAD+ research](/research) is clear that blood levels move. What the same literature does not yet establish is that raising blood NAD+ translates into hard clinical benefit in humans. A 2025 Nature Metabolism review of NAD+ precursor supplementation in human ageing concluded that clinical trials have shown limited efficacy and that human tissue-NAD+ data remain sparse [15]. Blood NAD+ elevation is well shown; longevity and disease prevention are not. This page, and this site, hold that line carefully. ## NAD+ as a dietary supplement vs its precursors An **NAD supplement** is, in nearly every case, not NAD+ at all — it is a precursor that the body converts into NAD+. The reason is chemistry: NAD+ is a charged dinucleotide of molecular weight 663.43 Da, too large and polar to cross cell membranes well when swallowed intact. So the rational oral approach uses smaller building blocks — NMN (nicotinamide mononucleotide), NR (nicotinamide riboside), and the vitamin-B3 compounds niacin and nicotinamide — that the cell's own machinery assembles into NAD+ [12]. Regulatory status matters here and is often misreported. NAD+ and its precursors are sold as dietary supplements, not approved drugs; none is FDA-approved to treat any disease. The status of NMN specifically is contested: the FDA has taken the position that NMN is excluded from the dietary-supplement definition because it was authorized for investigation as a drug. That is a live marketplace dispute over labeling, not a finding that NMN is unsafe or "banned." NAD+, NMN, NR, and nicotinamide are not prohibited by the World Anti-Doping Agency. ## What the studies actually measured Search interest in **NAD+ benefits** runs far ahead of the human evidence, so it is worth being precise about what was measured rather than what is hoped for. Measured and replicated: blood NAD+ rises with oral precursors [3][4]. Measured in single trials: ten weeks of oral NMN at 250 mg/day improved muscle insulin sensitivity in prediabetic, postmenopausal women, assessed by hyperinsulinemic-euglycemic clamp — though body composition and HbA1c did not change [1]. Measured mostly in animals: NMN reduced myocardial ischemia-reperfusion injury in mice in a manner dependent on NAD+ salvage and SIRT1 [7], and NAD+ precursors prevented cisplatin- and ischemia-induced acute kidney injury in mouse models [6]. The strongest organ findings are summarized in [NAD and heart health](/nad-and-heart-health). The honest frame: human anti-aging efficacy for hard endpoints remains preliminary as of the 2025 review [15]. This is a young, fast-moving field — the blood-level data are solid, the clinical-outcome data are not yet. It is worth naming what NAD+ is not, because the marketplace blurs it. NAD+ is not a peptide and not a protein — it is a dinucleotide, two nucleotides joined by phosphate groups, with the molecular formula C21H27N7O14P2. It is not vitamin B3 either; the B3 vitamins (niacin, nicotinamide) are precursors that feed NAD+ synthesis, while NAD+ is the finished coenzyme the cell builds from them [5]. And it is not an approved drug for any disease. Keeping those boundaries straight is most of what separates an accurate reading of this research from the claims that surround it. ## Where this site goes next The pages here are organized as a route through the evidence. The [NAD+ research](/research) page covers the salvage pathway, the NMN and NR human trials, and the mechanism. The [doses studied in the literature](/dosage) page lays out the research dose ranges and tolerability data — for context, never as instruction. [IV NAD therapy](/iv-nad) covers the injectable route, which carries the weakest controlled evidence and a documented contamination hazard. [NAD and heart health](/nad-and-heart-health) gathers the cardiac, kidney, and metabolic organ studies. The [frequently asked questions about NAD+](/faq) answer the common queries directly, and the [full reference list](/references) gives every citation with its DOI and PubMed link. --- A nocturnal traverse of the NAD+ literature — the heart, kidney, and muscle studies cited to source, the precursor-not-NAD+ distinction kept exact, and the trail marked where the human evidence thins; no clinic at the trailhead and nothing here dispensed, prescribed, or sold.