what is nad

What is NAD+? Nicotinamide Adenine Dinucleotide Explained | Vitality Supplements
Vitality Supplements · Science Guide

What is NAD+?

A complete guide to Nicotinamide Adenine Dinucleotide — what it is, what it does in every living cell, why NAD+ levels decline with age, and how NAD+ precursors like NMN relate to it as food supplement ingredients.

Science guide. Not medical advice. Not health claims.
The Fundamentals

What is NAD+?

NAD+ stands for Nicotinamide Adenine Dinucleotide. It is a coenzyme — a small molecule that works alongside enzymes to enable biochemical reactions — present in every living cell of every organism on earth, from bacteria to humans.

NAD+ was first identified in 1906 by Arthur Harden and William John Young during research into yeast fermentation. Over a century of subsequent research has established it as one of the most fundamental molecules in biology.

NAD+ participates in over 500 enzymatic reactions across human metabolism. Its two primary roles are as an electron carrier in cellular energy production and as a signalling molecule that regulates a wide range of cellular processes including DNA repair, gene expression and enzyme activation.

Without adequate NAD+, cells cannot produce energy efficiently, cannot repair DNA damage effectively, and cannot activate several important classes of regulatory enzymes. It is not an optional molecule — it is fundamental to life.

NAD+ was first identified in 1906. Over a century of research has established it as one of the most fundamental molecules in all of biology.
1906
Year identifiedBy Harden and Young
500+
Enzymatic reactionsNAD+ participates in
7
Sirtuin enzymesNAD+-dependent in humans
~50%
Decline documentedIn some tissues with age

NAD+ exists in two forms that interconvert during metabolism: NAD+ (the oxidised form) and NADH (the reduced form). NAD+ accepts electrons during metabolic reactions — particularly during the breakdown of nutrients — becoming NADH. NADH then donates those electrons to the mitochondrial electron transport chain to generate ATP, the cell's primary energy currency. The ratio of NAD+ to NADH is an important indicator of cellular metabolic state.

NAD+ & Ageing

Why NAD+ levels decline with age

One of the most consistently documented findings in ageing biology research is that NAD+ levels decline with age across multiple tissue types. This has been reproduced in peer-reviewed studies covering human liver, skeletal muscle, heart and brain tissue.

The decline is thought to result from several converging factors: reduced biosynthesis of NAD+ as precursor availability and enzyme activity change with age; increased consumption by NAD+-consuming enzymes — particularly PARP enzymes (activated by DNA damage, which accumulates with age) and CD38 (an NAD+-consuming enzyme whose expression increases with age); and reduced salvage pathway efficiency, which recycles NAD+ from breakdown products.

The practical consequence is that cells have less NAD+ available for energy production, DNA repair signalling and sirtuin enzyme activation as they age. This intersection of declining supply and increasing demand is what has made NAD+ metabolism a significant focus of longevity biology research.

NAD+ decline results from both reduced production and increased consumption — a combination that accelerates with age.

Important note: The above describes what peer-reviewed research has documented about NAD+ levels and ageing biology. This is not a health claim for any Vitality Supplements product. All products are food supplements and are not intended to diagnose, treat, cure or prevent any disease or medical condition.

PARP
DNA repair enzymesConsume NAD+, activated by damage
CD38
NAD+-consuming enzymeExpression increases with age
SIRT
Sirtuin enzymesRequire NAD+ to function
NMN
NAD+ precursorMost studied supplement route
The Sirtuin Connection

What are sirtuins?

Sirtuins are a family of NAD+-dependent deacetylase enzymes — they require NAD+ as a substrate to function. Seven sirtuins have been identified in humans (SIRT1 through SIRT7), each with distinct cellular locations and biological functions.

Sirtuins have been extensively studied in longevity biology research. They regulate a wide range of cellular processes including gene expression, DNA repair, metabolic regulation and stress responses. Because sirtuin activity is directly dependent on NAD+ availability, the decline in NAD+ levels with age is considered directly relevant to sirtuin function.

This relationship is also why certain polyphenols — particularly resveratrol and pterostilbene — are studied alongside NAD+ precursors in longevity research contexts. These compounds have been investigated as sirtuin activators, making the combination of an NAD+ precursor with a sirtuin-pathway polyphenol a logical area of research interest.

SIRT1
Nuclear — most studied
Regulates gene expression, metabolism and stress responses. The primary target of resveratrol research. Most extensively studied of the seven sirtuins in longevity biology contexts.
SIRT2
Cytoplasmic
Involved in cell cycle regulation and cytoskeletal organisation. Active in the cytoplasm and nucleus.
SIRT3
Mitochondrial
Located in mitochondria. Involved in mitochondrial metabolism, energy production and oxidative stress management.
SIRT4
Mitochondrial
Located in mitochondria. Involved in fatty acid oxidation and amino acid metabolism regulation.
SIRT5
Mitochondrial
Located in mitochondria. Involved in metabolic regulation and detoxification processes.
SIRT6
Nuclear — DNA repair
Involved in DNA repair, telomere maintenance and metabolic regulation. Studied in the context of genomic stability.
NAD+ Precursors

How to support NAD+ — the precursor approach

Because NAD+ itself is a relatively large molecule that does not easily cross cell membranes, research into NAD+ supplementation has focused primarily on precursor molecules — smaller compounds that the body can use to produce NAD+ via existing biosynthetic pathways.

Three main NAD+ precursors are available as food supplement ingredients in the UK:

Most studied precursor
NMN
Nicotinamide Mononucleotide. Enters cells and is converted to NAD+ via the salvage pathway. 30+ peer-reviewed human studies. Found naturally in edamame, broccoli and avocado. Vitality Supplements provides NMN at >99% β-NMN purity.
Established precursor
NR
Nicotinamide Riboside. Must first convert to NMN before becoming NAD+. More established research base than NMN historically. A distinct compound with different pharmacokinetics.
Reduced form of NMN
NMNH
Dihydronicotinamide Mononucleotide. The reduced form of NMN. A newer ingredient with active ongoing research. Distinct chemical properties under scientific investigation. Available from Vitality Supplements at 500mg per serving.

Why not supplement NAD+ directly? NAD+ supplements exist, but the molecule's relatively large size limits its ability to cross cell membranes efficiently. Precursor molecules like NMN are smaller and can be taken up by cells more readily. Published research on oral NAD+ supplementation has overwhelmingly focused on precursors rather than NAD+ itself for this reason.

Published Research

The NAD+ research landscape

NAD+ has been studied in biology for over a century. The specific area of research connecting NAD+ to ageing biology has accelerated significantly since the early 2000s, driven by advances in understanding sirtuins, PARP enzymes and the biology of cellular ageing.

The NAD+ decline finding: Multiple independent peer-reviewed studies have documented declining NAD+ levels with age across human tissue types. This is one of the most consistently reproduced findings in ageing biology and has been confirmed in liver, skeletal muscle, heart and brain tissue samples.

NMN and NAD+ levels: A systematic review covering 10 randomised controlled trials with 437 participants documented that oral NMN supplementation consistently elevated blood NAD+ levels in human subjects, across doses from 250 to 900mg per day, with a strong safety profile and no significant adverse events reported.

Sirtuins and longevity: Sirtuin research has produced an extensive body of published literature, with SIRT1 in particular studied extensively in longevity biology contexts. The connection between NAD+ availability and sirtuin activity is well established in the published literature.

Important caveat: The above describes published research about NAD+ as a molecule and NMN as a compound. These are not health claims for any Vitality Supplements product. All products are food supplements not intended to diagnose, treat, cure or prevent any disease.

A systematic review of 10 randomised controlled trials with 437 participants confirmed that oral NMN supplementation consistently elevated blood NAD+ levels in human subjects.
FAQ

Common questions

NAD+ (Nicotinamide Adenine Dinucleotide) is a coenzyme present in every living cell. It participates in over 500 enzymatic reactions, primarily as an electron carrier in cellular energy production (converting nutrients to ATP) and as a substrate for regulatory enzymes including sirtuins and PARP enzymes. It is one of the most fundamental molecules in biology — without it, cells cannot produce energy or carry out essential metabolic functions.
Yes — this is one of the most consistently documented findings in ageing biology. Multiple independent peer-reviewed studies have confirmed declining NAD+ levels with age across human tissue types including liver, skeletal muscle, heart and brain. The decline results from both reduced NAD+ biosynthesis and increased consumption by NAD+-consuming enzymes such as PARP (activated by DNA damage) and CD38 (which increases with age).
NAD+ is the coenzyme itself — present in every cell. NMN (Nicotinamide Mononucleotide) is a biosynthetic precursor — a smaller molecule the body uses to produce NAD+ via the salvage pathway. Because NAD+ is a relatively large molecule that does not cross cell membranes easily, supplementation research has focused on smaller precursor molecules like NMN. Read our full NMN guide →
Sirtuins are NAD+-dependent deacetylase enzymes — they require NAD+ as a substrate to function. Seven sirtuins (SIRT1-7) exist in humans, each with distinct locations and functions. They regulate gene expression, DNA repair, metabolic processes and stress responses. Because sirtuins require NAD+ to operate, declining NAD+ levels with age are considered directly relevant to sirtuin function in published research.
Resveratrol has been studied as an activator of sirtuin enzymes — particularly SIRT1. Since sirtuins require NAD+ to function, the research rationale for combining an NAD+ precursor (NMN) with a sirtuin-pathway polyphenol (resveratrol) is that sirtuin activation requires adequate NAD+ availability. Both are distinct compounds — this describes the research rationale, not a health claim. Read our full guide →
NAD+ is available as a supplement ingredient, but taking it directly is generally considered less effective than taking precursors such as NMN or NR. This is because the NAD+ molecule is relatively large and does not cross cell membranes easily. Published supplementation research has primarily focused on precursor molecules for this reason. NMN and NR are the most studied NAD+ precursors as food supplement ingredients.
Vitality Supplements provides NAD+ precursors as food supplement ingredients. Products include NMN Complete 1350mg (750mg NMN + TMG + Pterostilbene + Apigenin), NMNH 500mg and NMN + Trans-Resveratrol 1100mg (500mg NMN + 600mg Resveratrol). All products are UK manufactured and independently tested by an ISO/IEC 17025-accredited laboratory on every batch.

NAD+ precursors. Independently tested.

NMN Complete 1350mg · NMNH 500mg · NMN + Trans-Resveratrol 1100mg. UK manufactured. Every batch independently tested. Full dose transparency.

Shop Longevity Series → What is NMN?
Related Guides

Vitality Supplements is a UK-based longevity supplement brand. NMN Complete 1350mg , NMNH 500mg , NMN + Trans-Resveratrol 1100mg and AHCC 1000mg available at vitality-supplements.co.uk. Every batch independently tested by ISO/IEC 17025-accredited laboratory. UK manufactured. Free UK delivery. Food supplements — not medicines. Contact: info@vitality-supplements.co.uk.