What Is NAD+?
Nicotinamide Adenine Dinucleotide — NAD+ for short — is a coenzyme found in every living cell in the human body. It is not a drug, hormone, or exotic compound. It is a molecule your cells have relied on since the earliest stages of life, essential to the basic chemistry that keeps tissues alive and functioning.
NAD+ belongs to the vitamin B3 family. It exists in two forms: NAD+ (the oxidised form) and NADH (the reduced form). Cells constantly cycle between these two states as part of the energy-transfer process. Without this cycling, cellular metabolism stalls.
The challenge is that NAD+ levels decline significantly with age. Research suggests the average person has approximately half the NAD+ at age 60 that they had at age 20. This decline has led to growing scientific interest in whether restoring NAD+ levels could influence the biology of aging and age-related decline. It is an active and genuinely interesting area of research — though one where the human evidence is still catching up with the animal data.
How It Works — The Mechanism
NAD+ operates at the intersection of several critical cellular processes. Understanding its role requires a brief look at three key areas: energy production, DNA maintenance, and protein regulation.
ATP Production and Mitochondrial Function
Your cells produce energy in the form of ATP (adenosine triphosphate), primarily inside mitochondria. NAD+ is a required coenzyme in the electron transport chain — the process by which mitochondria convert nutrients into usable energy. Without adequate NAD+, this process becomes less efficient. Mitochondria are often described as the powerhouses of the cell, and NAD+ is a fundamental part of how that powerhouse runs.
Sirtuin Activation
Sirtuins are a family of proteins (SIRT1 through SIRT7 in humans) that regulate a wide range of biological processes including inflammation, stress response, metabolism, and gene expression. They are sometimes called longevity proteins. Critically, sirtuins are NAD+-dependent — they require NAD+ to function. When NAD+ levels fall, sirtuin activity drops with them. Researchers studying aging biology regard the NAD+-sirtuin axis as one of the more promising molecular pathways worth investigating.
DNA Repair via PARP Enzymes
PARP enzymes (Poly ADP-Ribose Polymerases) are involved in detecting and repairing DNA damage. They also consume NAD+ as a substrate. DNA damage accumulates with age, meaning PARP activity can increase — which in turn depletes NAD+ further. This creates a feedback loop that researchers are actively studying. The relationship between NAD+ availability and the efficiency of DNA repair mechanisms is a key focus in the aging biology field.
NAD+ Precursors: NMN and NR
NAD+ itself is not easily absorbed when taken orally because it cannot cross cell membranes directly. This is why research has focused on precursor molecules — compounds the body converts into NAD+. The two most studied are Nicotinamide Mononucleotide (NMN) and Nicotinamide Riboside (NR). Both are forms of vitamin B3 that the body can use to synthesise NAD+ intracellularly. IV administration is also used in some clinical and research contexts, bypassing the absorption question entirely.
What Does the Research Say?
The honest summary is this: the animal data is compelling; the human data is promising but limited. Both points are worth holding simultaneously.
Animal Studies
Studies in mice have consistently shown that supplementing with NMN or NR raises blood NAD+ levels significantly. More notably, several animal studies have reported improvements in muscle function, energy metabolism, insulin sensitivity, and even lifespan extension. Work from David Sinclair's laboratory at Harvard, among others, has demonstrated that raising NAD+ levels in aged mice reversed certain markers of vascular and muscle aging. These findings attracted widespread attention and helped drive the surge of interest in NAD+ biology.
It is important to note that mice and humans are not the same. Mice have significantly shorter lifespans and different metabolic rates. Results that hold in rodents do not always translate to humans — a pattern seen repeatedly across longevity research.
Human Trials
Human trials of NMN and NR have demonstrated one consistent finding: oral supplementation does raise NAD+ levels in blood. A 2020 study published in Nature Metabolism confirmed that NMN supplementation increased blood NAD+ in healthy older adults. A number of NR studies have shown similar results in terms of raising circulating NAD+ metabolites.
What the human trials have not yet firmly established is whether raising NAD+ levels translates into meaningful clinical outcomes — improved cognition, extended healthspan, measurable DNA repair improvements, or reduced disease risk. Some smaller studies have shown signals worth following up on, including improvements in muscle performance in older adults and potential benefits in metabolic markers, but these are early-stage findings. Larger, longer-duration randomised controlled trials are needed before firm conclusions can be drawn.
The field is moving. As of 2025, a growing number of Phase II and Phase III human trials are underway across several conditions including metabolic disease, neurodegeneration, and general aging biology. The next few years are likely to produce more definitive data.
Context for Irish Researchers
In Ireland, NAD+ precursors such as NMN and NR are primarily available as food supplements rather than regulated medicines. The Health Products Regulatory Authority (HPRA) oversees medicines and certain health products in Ireland, but food supplements operate under a separate framework. This means that product quality, purity, and dosing consistency can vary considerably between suppliers.
For researchers and those following the science, sourcing considerations matter. NAD+ precursors are sensitive to heat and moisture, and the difference between well-manufactured and poorly-stored product can be significant. When evaluating any supplier, certificates of analysis, third-party testing, and manufacturing standards are worth scrutinising.
Ireland's research community is increasingly engaged with longevity biology. Trinity College Dublin and University College Cork both have active research programmes in aging and metabolism. Internationally, the pace of NAD+ research is accelerating, with investment from both academic institutions and biotech companies. Irish clinicians and researchers are in a position to follow this literature closely and evaluate findings as they emerge.
It is worth noting that IV NAD+ administration, which delivers the molecule directly into the bloodstream rather than relying on oral absorption and conversion, is used in some private clinical settings in Ireland and the UK. This falls into a different regulatory and medical oversight category than oral supplements, and anyone interested in that route should do so under qualified medical supervision.
Key Takeaways
- NAD+ is a coenzyme present in every human cell, essential for energy production, DNA repair, and sirtuin activation.
- NAD+ levels decline by approximately 50% between early adulthood and age 60, which researchers believe may contribute to age-related biological decline.
- Precursor molecules NMN and NR can raise blood NAD+ levels — this is consistently demonstrated in human trials.
- Animal studies show significant benefits from NAD+ restoration; human clinical outcomes data is promising but not yet conclusive.
- Sirtuins — proteins involved in metabolism, inflammation, and longevity pathways — require NAD+ to function, making NAD+ availability central to their activity.
- In Ireland, NMN and NR are available as food supplements; product quality varies and sourcing standards matter.
- IV NAD+ is available in some private clinical settings and requires medical supervision.
- The research field is active and expanding — the next three to five years are likely to yield substantially more human data.
For research tools, protocol guides, and further reading on NAD+ and related compounds, visit irishpeptides.ie/free-tools.