# NAD+: The Redox Coenzyme, Read Through the Precursor Research > NAD+ is the coenzyme that cycles electrons through metabolism and is consumed by sirtuins, PARPs and CD38. A cited digest of the NMN and NR trials that raised blood NAD+ — supplement, not drug. A signal-clean readout of the literature: the precursor trials that moved whole-blood NAD+, the enzymes that consume it, and the gaps the studies leave open — each figure tagged by route and cited to source. ## The short version NAD+ (nicotinamide adenine dinucleotide — a fuel-handling helper molecule every cell uses to turn food into energy) is a coenzyme: a helper molecule that enzymes need to do their job. It carries electrons through metabolism, and it is also burned up by a set of maintenance enzymes (sirtuins, PARPs and CD38). Tissue NAD+ falls as we age. You cannot usefully swallow NAD+ itself — the molecule is too big and charged to absorb intact — so most products are precursors: smaller building blocks like NMN and NR that the body converts into NAD+. This page summarizes what the studies measured. It is not medical advice. ## What is NAD+? NAD+ is the cell's central redox carrier (redox is the chemistry of shuttling electrons to release energy). It shuttles electrons through glycolysis, the TCA cycle and oxidative phosphorylation to make ATP, the cell's energy currency, cycling between an oxidized form (NAD+) and a reduced form (NADH) [5]. It is a small endogenous metabolite — molecular weight `663.43 Da`, formula `C21H27N7O14P2`, CAS `53-84-9` — present in every living cell, not a peptide and not a drug. Beyond redox, NAD+ is a consumed substrate for signaling enzymes: [sirtuins, PARPs and CD38](/research) that govern DNA repair, gene regulation and inflammation [5]. The body makes its own NAD+ from three routes — de novo synthesis from tryptophan, the Preiss-Handler pathway from nicotinic acid, and a dominant salvage pathway that recycles nicotinamide through the rate-limiting enzyme NAMPT [7]. ### What is NAD+? NAD+ stands for nicotinamide adenine dinucleotide — two nucleotides joined by phosphate groups, with a nicotinamide ring on one end and an adenine ring on the other. It is the cell's redox coenzyme and a substrate for signaling enzymes, an endogenous metabolite found in every cell rather than a manufactured medicine. ### What does NAD stand for? NAD stands for nicotinamide adenine dinucleotide. The oxidized form is written NAD+ and the reduced form NADH; the two interconvert continuously as the coenzyme accepts and donates electrons through energy metabolism [5]. ### What does NAD do for the body? NAD+ carries electrons through energy metabolism — glycolysis, the TCA cycle and oxidative phosphorylation — to generate ATP, and it is consumed by sirtuins, PARPs and CD38, enzymes that govern DNA repair, gene regulation and inflammation [5][7]. Both roles draw on the same intracellular NAD+ pool. ### Is NAD a peptide? No. NAD+ is a dinucleotide coenzyme — two nucleotides linked by phosphate groups — not a peptide or protein and not an amino-acid chain. It is a small endogenous metabolite, molecular weight `663.43 Da` [1]. ### Is NAD just vitamin B3? NAD+ is built from vitamin-B3-family precursors — niacin, nicotinamide and nicotinamide riboside — but NAD+ itself is a larger dinucleotide coenzyme, not a vitamin [5]. [nicotinamide riboside (NR)](/nicotinamide-riboside) and NMN are the precursor forms most often taken orally to raise NAD+. ### What does NAD mean in medical terms? In biochemistry, NAD (nicotinamide adenine dinucleotide) is the cell's central redox coenzyme and a substrate for signaling enzymes. It is an endogenous metabolite and a dietary-supplement ingredient — not a prescription medicine for any condition. NAD+ is not FDA-approved to treat, prevent or cure any disease. ## Why NAD+ declines with age NAD+ falls with age across tissues. In human skin and brain the decline is on the order of `~50%` by middle to late life, tracking with weakening SIRT1/PGC-1alpha activity and mitochondrial function [6]. The fall is not only a supply problem — it is partly a consumption problem. The NAD-consuming ectoenzyme CD38 rises with age and inflammation; CD38-knockout mice are protected against age-related NAD+ decline and retain SIRT3 activity and mitochondrial function [2]. Senescent cells that accumulate with age feed this loop, secreting factors that activate CD38-expressing macrophages in fat and liver; clearing those senescent cells lowered the CD38+ macrophage burden and partly restored tissue NAD+ in mice [9]. That competition for a shrinking pool — sirtuins, PARPs and CD38 all drawing on the same NAD+ — is the rationale behind raising NAD+ with precursors. This is the [age-related NAD+ decline](/research) the rest of this site reads against. ## NAD+ as a dietary supplement: what the research says An NAD supplement is sold and regulated as a dietary supplement, not as an approved drug, and the active ingredient is almost always a precursor — NMN, NR or plain nicotinamide — rather than NAD+ itself. The strongest controlled human data are simple and consistent: oral precursors reliably raise whole-blood NAD+. In healthy overweight adults, `NR` at `100/300/1000 mg/day` for 8 weeks raised whole-blood NAD+ by `22%`, `51%` and `142%` respectively, with no flushing and no significant adverse-event difference from placebo [4]. In a multicenter trial of middle-aged adults, oral `NMN` at `300/600/900 mg/day` for 60 days raised blood NAD+ at days 30 and 60 across all groups versus placebo and improved six-minute walking distance [3]. Whether that blood-level rise translates to hard clinical outcomes is the open question — a 2025 review concluded human efficacy data remain limited and tissue-NAD+ data sparse [14]. The regulatory status of one precursor, NMN, is also 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, a marketplace dispute rather than a finding that NMN is banned [13]. See the [supplement and regulatory status](/faq) notes. ## NAD+ versus its precursors (NMN, NR) The single most important distinction on this site: oral NAD+ and its precursors are not interchangeable. NAD+ itself is large and charged, and is not freely taken up intact by most cells, so plain oral 'NAD+' capsules are widely considered an inefficient way to raise the coenzyme. The rational oral route is a precursor — a smaller building block the body converts into NAD+. [nicotinamide riboside (NR)](/nicotinamide-riboside) is converted to NMN by NRK kinases, then to NAD+ [5]; NMN sits one biochemical step from NAD+. Throughout this site, every route-specific figure carries a channel tag — ORAL-PRECURSOR, IV, or INJECTABLE — so a trial of oral NMN is never read as 'taking NAD+'. When a study raised blood NAD+ by `142%`, it dosed NR, not NAD+ [4]; when a study improved muscle insulin sensitivity, it dosed `250 mg/day` of NMN, not NAD+ [11]. Read [NMN in aging research](/nmn) and the precursor record alongside the coenzyme itself. ## What this readout covers This is an editorial digest of the published NAD+ literature, organized like an instrument panel: confirmed findings, preclinical signals, and honest gaps, each tagged by route and cited. The [doses studied in the literature](/dosage) sit on /dosage as research figures, never as instructions. The mechanism — redox cycling plus the sirtuin/PARP/CD38 enzymes that consume NAD+ — sits on /research alongside [IV NAD+ tolerability](/research) and the precursor trials. Every quantitative claim resolves to a study in the [full reference list](/references). What this digest does not do is recommend a product, a dose, or a route; it reports what specific studies measured. ### What is NAD supplement used for? NAD+ is an endogenous coenzyme present in every cell; it is marketed as a dietary supplement — usually as the precursors NMN or NR — and studied for whether raising blood NAD+ affects metabolism and age-related decline [4][14]. It is not an FDA-approved treatment for any disease. ### What is an NAD injection? An NAD injection or IV infusion delivers NAD+ directly into the bloodstream, bypassing oral absorption. It is a compounded wellness therapy, not an FDA-approved product, and controlled evidence for it is limited; infused NAD+ is rapidly cleared from plasma, with near-complete plasma removal in the first hours of an infusion [14]. --- A signal-clean readout of the NAD+ literature — the precursor trials that actually moved whole-blood NAD+ logged in their own oral channel, plain oral NAD+ and the weak-evidence IV route kept on separate channels, and the unsettled NMN status reported as filed; no clinic behind this console and nothing here dosed, dispensed, or sold.