NAD+ is the cell's central redox coenzyme, read here through metabolism and the human precursor trials.

The short version

NAD+ (a fuel-handling helper molecule every cell uses to turn food into energy) is not a drug and not a single product you buy. It is a coenzyme — a helper molecule an enzyme needs to do its job — that every cell makes for itself. Most pills sold to "raise NAD+" are actually precursors (building blocks the body converts into NAD+), because NAD+ itself is too large to absorb well by mouth. The two best-studied precursors are NMN and NR. This site documents what the studies measured, in plain terms, with sources. It gives no doses to take and sells nothing.

What is NAD+?

NAD+ is the most-used helper molecule in your metabolism. It carries electrons through the three stages cells use to make ATP (the cell's energy currency) — glycolysis, the TCA cycle, and the electron transport chain — flipping between an oxidized form (NAD+) and a reduced form (NADH) as it works ^[5]. NAD+ is also the consumed raw material for a set of signaling enzymes: sirtuins (a family of cellular-maintenance enzymes that cannot work without it), PARPs (DNA-repair enzymes), and CD38 (an enzyme that rises with age and inflammation) ^[5].

Tissue NAD+ falls with age. A foundational 2021 review in Nature Reviews Molecular Cell Biology traced that decline across yeast, worms, mice, and humans and named the sirtuin, PARP, and CD38 enzymes that compete for the shrinking pool ^[5]. One mouse study identified CD38 as the principal age-rising consumer; deleting CD38 protected animals from the age-related NAD+ drop ^[2]. That decline-and-restore logic is the entire rationale behind NAD+ precursor supplements.

NAD stands for nicotinamide adenine dinucleotide. It is built from two ring systems — a nicotinamide ring and an adenine ring — joined by two bridging phosphates, with the molecular formula C21H27N7O14P2 and a molecular weight near 663.43 Da. It is a small endogenous metabolite, not a peptide and not a protein.

What the human precursor trials have measured

The strongest human data are for the oral precursors, not for NAD+ taken directly. In healthy overweight adults, nicotinamide riboside (NR) raised whole-blood NAD+ by 22%, 51%, and 142% at 100, 300, and 1000 mg/day over eight weeks — a clean dose-dependent rise, with no flushing and no significant adverse-event difference from placebo at any dose ^[4]. A multicenter, double-blind RCT of nicotinamide mononucleotide (NMN) at 300, 600, and 900 mg/day for 60 days raised blood NAD+ at days 30 and 60 across every NMN group versus placebo, improved walking distance, and identified 600 mg/day as the optimal dose, with no safety issues at any dose ^[3].

Functional endpoints are more mixed than the blood-NAD+ numbers. Ten weeks of NMN at 250 mg/day improved muscle insulin sensitivity research in prediabetic, postmenopausal women — measured by the gold-standard hyperinsulinemic-euglycemic clamp — without changing body composition or HbA1c ^[1]. A 2024 systematic review of ten randomized trials (437 participants) found NMN improved gait speed, sit-to-stand performance, and six-minute walking distance, with no serious adverse events ^[15]. A 2025 Nature Metabolism review of the whole field concluded that raising blood NAD+ is well demonstrated, but human efficacy for hard clinical endpoints remains limited ^[14].

Is NAD just vitamin B3?

NAD+ is built from vitamin-B3-family precursors — niacin, nicotinamide, and the newer NR and NMN — but NAD+ itself is the larger working coenzyme the body assembles from them. NR and NMN are precursors, not NAD+ taken directly. NR sits two enzymatic steps from NAD+; NMN sits one. That is the practical reason oral "NAD+ boosters" are precursors: NAD+ is large and charged, so it is poorly absorbed intact, while the smaller precursors are absorbed and converted inside cells ^[8]. The distinction matters throughout this digest — an oral-NMN or oral-NR trial is never the same as "taking NAD+."

What does NAD do for the body?

NAD+ carries electrons through glycolysis, the TCA cycle, and oxidative phosphorylation to make ATP, and it is the consumed substrate for sirtuins, PARPs, and CD38 that govern DNA repair, gene regulation, and inflammation ^[5]. In short, it both powers metabolism and supplies the maintenance enzymes that keep cells in order — two distinct jobs done by one molecule.

What is NAD supplement used for?

As a supplement topic, NAD+ is studied — mostly as the oral precursors NMN and NR — for raising blood NAD+, with mixed evidence on functional endpoints ^[4][1]. It is a dietary supplement, not an approved drug. Raising blood NAD+ is well demonstrated in randomized trials; benefit for hard clinical endpoints remains limited ^[14].

Blood NAD+ versus benefit: the gap worth knowing

One distinction shapes how to read every NAD+ headline: raising the level is not the same as proving a benefit. The oral precursors reliably raise whole-blood NAD+ in a dose-dependent way — that part is settled across multiple randomized trials ^[4][3]. What is far less settled is whether that measurable rise produces outcomes a person would notice or a doctor would track. Some controlled trials have found specific gains (muscle insulin sensitivity, walking distance, gait speed) ^[1][15], but the 2025 Nature Metabolism review of the whole field concluded that human efficacy for hard clinical endpoints remains limited and that tissue-level NAD+ data are sparse ^[14]. So the honest one-line summary is: the chemistry moves, the clinical case is still being built. This digest keeps those two things separate on every page.

What does NAD stand for, and is it a peptide?

NAD stands for nicotinamide adenine dinucleotide; the plus sign in NAD+ marks its oxidized form, and the reduced form is NADH ^[5]. It is not a peptide and not a protein — it is a small dinucleotide coenzyme (nicotinamide plus adenine, joined by two phosphates), formula C21H27N7O14P2, molecular weight near 663.43 Da, found in every living cell ^[5]. In medical terms, NAD names the cell's central redox coenzyme, not a disease or drug.

How this reference is organized

This is a documentation-style digest, not a clinic and not a store. The pages are organized like a reference. NAD+ and metabolism collects the human metabolic-muscle trials. IV NAD+ therapy documents the infusion and injection routes, their pharmacokinetics, and their quality risks. The research page maps the biosynthetic pathways and the consuming enzymes; the dosage page lists the doses studied in the literature by route, as research context only. Every quantitative claim resolves to a numbered entry in the study references. No page recommends a dose, names a brand, or sells anything.