# NAD+: The Redox Coenzyme and Why Most Supplements Are Precursors > NAD+ is the redox coenzyme every cell uses to make energy. Most oral supplements are precursors (NMN, NR), not NAD+ itself. A cited research digest of what the human trials measured. A color-coded reading of the literature: the redox biochemistry, the human precursor trials for NMN and NR, the doses that were studied, and the places where the IV-therapy evidence runs thin. Every quantitative claim is cited. ## In plain English NAD+ (a fuel-handling helper molecule that every cell uses to turn food into energy) is one of the most-used molecules in the body. Levels drift down with age. That has made it a popular supplement target — but here is the catch this whole site is built around: NAD+ itself is large and poorly absorbed when swallowed, so almost every oral product is actually a *precursor* (a smaller building block the body converts into NAD+ — NMN and NR are the common ones). When a study says people "took NAD+," they almost always took a precursor. This page sorts out what NAD+ is, what the human trials measured, and what is still unproven. ## What Is NAD+? NAD+ is a coenzyme (a helper molecule an enzyme needs to do its job) found in every living cell. Chemically it is a dinucleotide — a nicotinamide ring and an adenine ring joined by two phosphate groups (formula C21H27N7O14P2, molecular weight 663.43 Da) [8]. It exists in two interconverting forms: the oxidized NAD+ and the reduced NADH. The cell shuttles electrons between them, which is how it banks and releases energy. Three facts frame everything below. First, NAD+ is *endogenous* — your cells synthesize it from tryptophan and from B3-family vitamins through the salvage pathway [5]. Second, tissue NAD+ declines with age across model organisms and humans [5][7]. Third, NAD+ is not a drug: it is sold as a dietary supplement, and it is not approved by the FDA to treat any disease. This site summarizes the published research; it is not medical advice and recommends no product or dose. ## What does NAD do for the body? NAD+ does two jobs at once. As a *redox* (chemistry that shuttles electrons to release energy) carrier, it ferries electrons through glycolysis, the TCA cycle, and the mitochondrial electron transport chain to drive ATP synthesis — the cell's energy currency [9][10]. As a *consumed substrate*, it is the raw material spent by signaling enzymes: sirtuins (a family of cellular-maintenance enzymes that cannot work without NAD+), PARPs (DNA-repair enzymes), and CD38 [5][8]. Those enzymes physically break NAD+ apart to do their work, which is why the pool has to be continually resynthesized. That dual role — energy carrier and signaling fuel — is why declining NAD+ has been linked to metabolic dysfunction with age [5][10], and why raising it has become a research target. The enzyme CD38 rises with age and consumes NAD+; in mice, deleting CD38 preserved NAD+ levels and mitochondrial function [2]. ## What the Research Reports on NAD+ The single most reproducible human finding is pharmacodynamic: oral precursors reliably and dose-dependently raise blood NAD+. In a randomized trial of healthy overweight adults, nicotinamide riboside (NR) raised whole-blood NAD+ by 22%, 51%, and 142% at 100, 300, and 1000 mg/day over 8 weeks [4]. In a multicenter, double-blind RCT in middle-aged adults, NMN at 300-900 mg/day for 60 days raised blood NAD+ at every dose versus placebo (p≤0.001), with 600 mg/day identified as the optimal dose [3]. Functional outcomes are more mixed. Ten weeks of oral NMN at 250 mg/day improved muscle insulin sensitivity in prediabetic postmenopausal women, with no change in body composition or HbA1c [1]. A 2025 Nature Metabolism review of the human evidence concluded that trials have shown limited efficacy for hard clinical endpoints and that tissue-specific NAD+ data remain sparse [15]. The honest summary: raising blood NAD+ is well established; translating that to disease or longevity benefit in humans is not. See [what the human trials measured](/research) for the full breakdown, or the [NAD supplement research](/nad-supplement) overview. ## NAD+ vs NMN and NR — the distinction this site keeps Three things share the "NAD" headline and are constantly conflated. **NAD+** is the coenzyme itself. **NMN** (nicotinamide mononucleotide) is a precursor one biochemical step from NAD+. **NR** (nicotinamide riboside) is a B3-family precursor that the body converts to NMN via the NRK1/NRK2 kinase route — a pathway distinct from the niacin (Preiss-Handler) route, first defined in 2004 [6]. The practical reason this matters: NAD+ itself is large and charged and is not freely taken up intact by most cells, so most researchers treat oral precursors as the rational way to raise NAD+ [7]. A capsule labeled "NAD+" and a capsule of NMN or NR are not the same thing biochemically. The [NAD+ vs NMN and NR](/nmn-vs-nr) page lays out the precursor routes side by side; the [frequently asked questions about NAD+](/faq) cover the most common points of confusion. --- A color-coded poster wall of the NAD+ record — the coenzyme, its oral precursors NMN and NR, and the thin IV-therapy evidence each set in its own block and cited to the study that measured it, with the precursor-not-NAD+ distinction kept exact; no clinic behind the wall and nothing here dosed, compounded, prescribed, or sold.