# NAD+: What the Precursor and Brain Research Actually Measured > NAD+ is the cell's central redox coenzyme; tissue levels fall with age. A research digest of the oral precursor trials (NMN, NR), the brain studies, and the IV gaps — every figure cited. A developer-console reading of the published literature: the oral precursors that reliably raise blood NAD+, the brain and cognition trials, the IV-therapy evidence gaps — each datum logged to its source and tagged by evidence strength. ## The short version NAD+ (a fuel-handling helper molecule every living cell uses to turn food into usable energy) is not a drug and not a single product — it is a natural coenzyme (a helper molecule an enzyme needs to do its job). Cells make it themselves, and the amount in your tissues drops as you age. Most things sold as "NAD+" are actually precursors (building blocks the body converts into NAD+ — NMN and NR are the common ones), because NAD+ itself is too large to absorb well by mouth. This site reads the published studies straight: what was measured, in whom, at what dose. ## What the NAD+ literature establishes NAD+ — nicotinamide adenine dinucleotide — is the cell's central redox carrier (the NAD+/NADH pair that shuttles electrons through metabolism to make ATP) and a consumed substrate for the signaling enzymes sirtuins, PARPs and CD38 that govern DNA repair, gene regulation and inflammation [5]. Every living cell makes its own NAD+ from scratch, recycles it, and spends it; the molecule is a metabolite, not a manufactured drug. Tissue NAD+ declines with age across model organisms and humans, a fall driven in part by the rising NAD+-consuming ectoenzyme CD38 [2][5]. That decline is the rationale behind the entire NAD+ supplement category — and the single most important distinction on this site is that NAD+ is the downstream coenzyme, while [NMN vs NR precursors](/research) are the building blocks studied to raise it. The controlled human evidence is overwhelmingly about those precursors, taken orally. In a randomized trial, oral nicotinamide riboside (NR) raised whole-blood NAD+ by 22%, 51% and 142% at 100, 300 and 1000 mg/day over 8 weeks, with no significant adverse-event difference from placebo [4]. A multicenter trial of oral NMN at 300-900 mg/day for 60 days raised blood NAD+ at every dose versus placebo (p ≤ 0.001) and improved six-minute walking distance [3]. NAD+ levels can be moved. Whether moving them changes hard clinical outcomes in humans is a separate, still-open question [1]. The regulatory picture is worth stating up front, because the marketing around this molecule is loud. NAD+ is not FDA-approved for any disease; it is sold as a dietary supplement, and most oral products supply precursors rather than NAD+ itself [12]. NMN's status as a supplement is contested — the FDA has taken the position that it was excluded from the supplement definition after being authorized for drug investigation, a marketplace dispute rather than a settled ban [1]. Injectable NAD+, used in IV wellness clinics, is compounded rather than approved, and a compounded NAD+ injection has carried a Class I recall for endotoxin contamination. This site reports those facts as filed and sells nothing. ## What is NAD supplement used for? NAD+ is an endogenous redox coenzyme found in every cell; as a supplement category it is studied for raising NAD+ — usually via precursors such as NMN or NR — in the context of aging, metabolism and mitochondrial function. It is sold as a dietary supplement, not an approved treatment for any disease. A 2025 review concluded human efficacy data for clinical endpoints remain limited [1]. ## What does NAD do for the body? NAD+ is the cell's central redox carrier (NAD+/NADH) for ATP production and a consumed substrate for the enzymes sirtuins, PARPs and CD38, which govern DNA repair, gene regulation and inflammation [5]. Its levels decline with age across tissues [2][5]. The supplement category aims to counter that decline, but raising blood NAD+ and changing health outcomes are not the same thing [1]. ## What does NAD stand for? NAD stands for nicotinamide adenine dinucleotide. The two interconverting forms are the oxidized NAD+ and the reduced NADH; NAD+ accepts electrons during catabolism and NADH donates them in the mitochondrial electron transport chain to drive ATP synthesis. Older literature also calls it Coenzyme I or DPN (diphosphopyridine nucleotide). ## What does NAD mean in medical terms? In biochemistry, NAD (nicotinamide adenine dinucleotide) is a coenzyme central to redox metabolism and to NAD+-consuming signaling enzymes — sirtuins, PARPs and CD38 [5]. It is an endogenous metabolite synthesized in every human cell, not a prescription drug. Its decline with age is the rationale for studying precursor supplementation [2]. ## Is NAD just vitamin B3? No. NAD+ is a dinucleotide coenzyme built from vitamin-B3-family precursors. Niacin, nicotinamide, and the studied precursors NR and NMN all feed into NAD+ synthesis [10], but NAD+ itself is the larger downstream coenzyme — molecular weight 663.43 Da — not the vitamin. The precursors are the inputs; NAD+ is the pool they compile into. ## Is NAD a peptide? No. NAD+ is not a peptide. It is a dinucleotide (nicotinamide adenine dinucleotide) made of a nicotinamide ring and an adenine ring joined by two bridging phosphates, molecular formula C21H27N7O14P2. A peptide is a chain of amino acids; NAD+ is a coenzyme built from two nucleotide units, a structurally different class of molecule entirely. ## Why NAD+ falls with age The reason an entire research field cares about a humble coenzyme is that NAD+ does not stay constant over a lifetime — it declines, and the decline tracks with metabolic and mitochondrial trouble [5]. One major driver is consumption. CD38, an NAD+-degrading ectoenzyme, rises with age and inflammation, draining the shared pool faster than salvage can refill it; in mice, deleting CD38 preserves NAD+ and downstream SIRT3 activity and protects mitochondrial function [2][11]. Senescent cells contribute too, secreting inflammatory factors that activate CD38-bearing immune cells and accelerate the local NAD+ drop [5]. Falling NAD+ has been proposed to push cells toward *pseudohypoxia* — a breakdown in nuclear-mitochondrial communication that mimics low oxygen even when oxygen is adequate — offering a mechanistic thread from low NAD+ to impaired energy metabolism [5]. This is the chain the supplement category is betting on: restore the substrate, restore the function. The bet is well supported in rodents and at the level of the biomarker in humans; it is not yet proven at the level of human clinical outcomes [1]. ## How to read this digest Findings carry a build-status tag so you can see at a glance where each one stands. **CITATION-CONFIRMED** marks results verified to a published trial — the precursor blood-NAD+ studies [3][4], the NMN insulin-sensitivity result [6], the NADPARK cerebral-NAD+ readout [7]. **GAP** marks honest limits — the 2025 review on unproven clinical endpoints [1], the cognition trial that raised NAD+ but did not improve scores [14]. **PRECLINICAL** marks rodent or in-vitro-only findings [2][13]. **CAUTION** marks the IV/injectable risks [8]. The two dealt landing pages go deeper: [NAD and the brain](/nad-and-the-brain) reads the neuro literature, and [IV NAD therapy](/iv-nad-therapy) reads the unapproved infusion route. See also the [doses studied in the research](/dosage) and the [full reference list](/references). --- A build-log reading of the NAD+ literature, traced from salvage pathway to brain — the coenzyme kept distinct from its NMN and NR precursors, the oral trials kept apart from the rapidly-cleared IV route, and the contested NMN supplement status logged as filed; no clinic compiles behind this console and nothing here is dosed, compounded, prescribed, or sold.