Quick answer: NAD+ (nicotinamide adenine dinucleotide) is a coenzyme found in every living cell. Its main job is to help turn the food you eat into usable cellular energy, and it also acts as a helper molecule for hundreds of enzymes involved in DNA repair, metabolism, and healthy aging.* You can't avoid NAD+, you'd die without it, and while its levels have long been described as declining with age, newer whole-blood research is still settling that question.
If you've started reading about longevity, "NAD+" is probably the acronym you keep tripping over. It sounds technical, and most explanations are either oversimplified marketing or dense biochemistry. This guide sits in the middle: a plain-English, science-grounded answer to what NAD+ actually is, what it does, why it falls with age, and what the honest evidence says about supporting it, written for adults (our readers are mostly women in midlife) who want the real picture, not hype.
What is NAD+?
NAD+ is a coenzyme, a small "helper" molecule that enzymes need in order to do their work. Its full name is nicotinamide adenine dinucleotide, and the "+" refers to its oxidized, electron-accepting form. It exists in every cell of your body, from your skin to your brain to your muscles, and it is one of the most abundant and essential molecules in human biology.
A useful way to picture it: if your cells are tiny factories, NAD+ is part of the electrical wiring. It doesn't do the manufacturing itself, but almost nothing gets built without it. Your body makes its own NAD+ continuously from building blocks in your diet, recycling it thousands of times a day.
In one sentence: NAD+ is a coenzyme present in all living cells that helps convert nutrients into cellular energy and supports the enzymes involved in DNA repair, metabolism, and healthy aging.*
What does NAD+ do in the body?
NAD+ has two broad jobs: it carries energy, and it acts as a "fuel" for a family of regulatory enzymes.
1. Energy metabolism. NAD+ is central to how cells produce ATP, the energy currency of life. During glycolysis, the citric acid cycle, and oxidative phosphorylation, NAD+ shuttles electrons by flipping between its two forms, NAD+ (oxidized) and NADH (reduced). This redox cycling is a core part of cellular energy metabolism and normal cellular function.*
2. Signaling and repair. Beyond energy, NAD+ is consumed by enzymes that regulate important cellular processes. Two families matter most here: sirtuins, which are involved in gene expression and metabolic regulation, and PARPs, which detect and help repair DNA damage. A third enzyme, CD38, also consumes NAD+ as part of immune signaling. Because these enzymes burn through NAD+ to function, the cell is constantly rebuilding its supply.
NAD+ vs NADH and the NAD+ precursors: what's the difference?
People often confuse NAD+ with NADH and with its "precursors" like NMN and NR. They're related but not the same. Here's a quick map.
| Molecule | What it is | Role in plain English |
|---|---|---|
| NAD+ | The oxidized, electron-accepting form of the coenzyme | The "empty" carrier, ready to pick up electrons during energy production |
| NADH | The reduced, electron-carrying form | The "loaded" carrier that delivers electrons to make ATP, then becomes NAD+ again |
| NMN | Nicotinamide mononucleotide, a direct precursor | A building block the body can convert toward NAD+ production* |
| NR | Nicotinamide riboside, another precursor | A building block that becomes NMN, then feeds NAD+ pathways* |
| Niacin (B3) | The classic dietary vitamin form | The original food source the body uses to build NAD+ |
So NAD+ and NADH are the same coenzyme in two states, while NMN, NR, and niacin are the raw materials your body uses to make more of it, and if the precursor-versus-coenzyme distinction is exactly what brought you here, our NMN vs NAD+ explainer → draws it out in full. For a deeper comparison of the two most-discussed precursors, see NMN vs NR →
Does NAD+ decline with age?
The long-held view: as we get older, the body may make less NAD+ and consume more of it at the same time. Human studies have long described NAD+ as declining with age, for example in muscle with age-related loss, and a 2026 whole-blood study across 7 cohorts (PMID 42135539) found levels did not clearly vary with age. The science is still settling, and exact figures vary by tissue and measurement method.
Two shifts are proposed to drive it. First, the enzyme NAMPT, which helps the body recycle NAD+, becomes less active with age, lowering production. Second, NAD+-consuming enzymes ramp up. The enzyme CD38 in particular rises with age and has been identified as a major driver of age-related NAD+ decline in research published in Cell Metabolism. At the same time, accumulating DNA damage keeps PARP enzymes busy, and they consume NAD+ to do their repair work, so demand goes up just as supply goes down.
This is why NAD+ has become such a central topic in healthy aging research: it sits at the intersection of energy, metabolism, and cellular maintenance, all of which shift with age.*
How does the body make NAD+?
Your body builds NAD+ through three routes: the de novo pathway (from the amino acid tryptophan), the Preiss-Handler pathway (from niacin), and, most importantly for daily turnover, the salvage pathway, which recycles NAD+ breakdown products back into fresh NAD+. The salvage pathway is where precursors like NMN and NR enter the picture, which is why they're studied so heavily in the longevity field.* To see how these pieces fit into a daily routine, read The Longevity Stack Explained →
Can you raise NAD+ with supplements?
This is where honesty matters most. The research here is real but still developing, and it's mostly centered on NAD+ precursors (NMN, NR), which are the most-studied route for supporting the body's own NAD+ production.
The most-cited human study is a 2021 randomized, placebo-controlled trial published in Science, in which 10 weeks of NMN improved muscle insulin sensitivity in a small group of postmenopausal women with prediabetes. It was an early, small trial, promising, but not proof of broad benefit. Animal studies, such as long-term NMN administration in mice, have shown effects on energy metabolism and age-associated physiological measures, but mouse results don't automatically translate to humans.
What we can say accurately: precursors are studied for their role in supporting NAD+ biosynthesis and cellular energy metabolism.* What we should not say is that any oral supplement is a sure way to "boost" NAD+ throughout the body, or that it treats any condition. The honest position is that this is an active and encouraging area of research, not a settled one. We lay out exactly what that research does and does not support in NAD+ Benefits: What the Science Says →.
How to support healthy NAD+ levels
Before any supplement, the everyday basics influence the systems NAD+ depends on. A practical, evidence-informed checklist:
- Prioritize sleep, 7-9 consistent hours supports the metabolic and repair processes NAD+ is involved in.
- Move regularly, both aerobic and resistance exercise are associated with healthier cellular energy metabolism.
- Eat whole foods with adequate protein, including natural sources of niacin (B3), an NAD+ building block.
- Protect your skin from excess sun, UV damage increases the DNA-repair demand that consumes NAD+.
- Keep alcohol moderate, heavy intake taxes the same metabolic pathways.
- Consider precursors thoughtfully, if you choose to add NMN or NAD+ support, look for transparent labels, meaningful serving levels, and third-party testing, and talk to your clinician first.*
What we know, and what we don't
We know NAD+ is essential and central to energy metabolism and cellular maintenance, and that its levels have long been described as declining with age, most consistently in animal studies. We know precursors can raise NAD+ markers in early human studies. What we don't yet know is how much long-term supplementation changes meaningful health outcomes in healthy people, the ideal doses, or who benefits most. Good science holds both the promise and the uncertainty at once, and so should any brand selling in this category.
What NAD+ (and NAD+ supplements) will not do
Stated plainly: NAD+ and NAD+ supplements are not a fountain of youth and not a medicine, they will not replace sleep, movement, and nutrition, and they come with no promise of a fixed or overnight result. They are not a substitute for medical care.
Where CELLSHE fits
CELLSHE makes a focused range built around NAD+ biology for women in midlife. Our NAD+ → ($89, or $75 monthly) formula is designed to support cellular function and healthy aging,* and pairs NAD+ with quercetin, a flavonoid studied alongside NAD+ pathways,* plus resveratrol for antioxidant and polyphenol support.* If you'd rather start at the precursor layer, NMN 500 → ($79, or $65 monthly) supports NAD+ biosynthesis and cellular energy production.* We don't promise miracles, we offer transparent labels, third-party testing, and evidence-informed serving levels. Not sure where to begin? The free Cellular Age Check → is a 2-minute starting point. For more on why this coenzyme matters as we age, read Why NAD+ Matters →
Frequently asked questions about NAD+
What does NAD+ stand for?
NAD+ stands for nicotinamide adenine dinucleotide. The "+" indicates its oxidized form, which is ready to accept electrons during energy production.
Is NAD+ the same as NADH?
They're the same coenzyme in different states. NAD+ is the oxidized (electron-accepting) form; NADH is the reduced (electron-carrying) form. Cells constantly cycle between the two to move energy.
Is NAD+ the same as NMN or NR?
No. NMN and NR are precursors, building blocks the body can use to make NAD+. NAD+ is the finished coenzyme itself.*
Does NAD+ really decline with age?
It is still being worked out. Human studies have long described NAD+ as declining with age in many tissues, driven by both reduced production and increased consumption by enzymes like CD38 and PARPs, but a 2026 whole-blood study across seven cohorts (PMID 42135539) found levels did not clearly vary with age. Exact amounts vary by study and tissue.
Can I get NAD+ from food?
You don't eat NAD+ directly in meaningful amounts, but your body builds it from dietary precursors such as niacin (vitamin B3) and tryptophan, found in many whole foods.
Should I take an NAD+ supplement?
That's a personal decision best made with your healthcare provider, especially if you take medication or have a medical condition. Supplements are one part of a broader healthy-aging routine, not a substitute for sleep, movement, nutrition, or medical care.
References
- Verdin, E. (2015). NAD+ in aging, metabolism, and neurodegeneration. Science. PMID: 26785480. pubmed.ncbi.nlm.nih.gov/26785480
- Rajman, L., Chwalek, K., & Sinclair, D. A. (2018). Therapeutic potential of NAD-boosting molecules: the in vivo evidence. Cell Metabolism. PMID: 29514064. pubmed.ncbi.nlm.nih.gov/29514064
- Camacho-Pereira, J., et al. (2016). CD38 dictates age-related NAD decline and mitochondrial dysfunction through a SIRT3-dependent mechanism. Cell Metabolism. PMID: 27304511. pubmed.ncbi.nlm.nih.gov/27304511
- Yoshino, M., et al. (2021). Nicotinamide mononucleotide increases muscle insulin sensitivity in prediabetic women. Science. PMID: 33888596. pubmed.ncbi.nlm.nih.gov/33888596
- Mills, K. F., et al. (2016). Long-term administration of nicotinamide mononucleotide mitigates age-associated physiological decline in mice. Cell Metabolism. PMID: 28068222. pubmed.ncbi.nlm.nih.gov/28068222
- Imai, S., & Guarente, L. (2014). NAD+ and sirtuins in aging and disease. Trends in Cell Biology. PMID: 24786309. pubmed.ncbi.nlm.nih.gov/24786309
