NAD+: The Molecule Behind Cellular Energy, Repair & Ageing

Every second of every day, trillions of cells throughout your body are performing an extraordinary amount of work.

They convert food into usable energy.

They repair damaged DNA.

They respond to stress.

They communicate.

They maintain tissues.

And behind many of these processes sits a molecule that has become one of the most talked-about subjects in longevity science:

NAD+.

NAD+ — short for nicotinamide adenine dinucleotide — isn't a peptide, hormone or stimulant.

It's a naturally occurring coenzyme found in every living cell.

And without it, some of the most fundamental processes required for life simply couldn't operate normally.

So why has NAD+ suddenly become synonymous with anti-ageing?

As usual, the real science is more interesting than the headline.

What Exactly Is NAD+?

NAD exists primarily in two interconnected forms:

NAD+ — the oxidised form

and

NADH — the reduced form.

These molecules continuously move between states as part of reactions involved in cellular metabolism.

One of NAD's fundamental roles is acting as an electron carrier.

When nutrients from food are metabolised, electrons are transferred through a series of biochemical reactions.

NAD+ accepts electrons and becomes NADH.

NADH can subsequently donate those electrons to processes involved in producing ATP — adenosine triphosphate, the molecule cells use as an immediate source of energy.

So although NAD+ is often advertised as an “energy molecule”, it doesn't provide energy in the way food does.

It helps cells convert fuel into usable cellular energy.

That distinction matters.

NAD+ & The Mitochondria

This brings us to the mitochondria.

Often described as the powerhouses of the cell, mitochondria convert energy derived from nutrients into ATP through processes including oxidative phosphorylation.

NAD+/NADH participates directly in this system.

This means NAD availability is closely connected with:

cellular energy metabolism mitochondrial function redox balance metabolic flexibility responses to cellular stress.

But NAD+ does considerably more than help generate ATP.

And this is where longevity researchers became particularly interested.

NAD+ Is Also Consumed by Cellular Repair Systems

NAD+ isn't simply recycled between NAD+ and NADH.

Some enzymes actually consume NAD+ as part of their normal activity.

Three particularly interesting families are:

Sirtuins

Sirtuins are NAD+-dependent enzymes involved in processes including gene regulation, metabolism, mitochondrial biology and cellular stress responses.

Their dependence on NAD+ is one reason NAD metabolism became closely linked with ageing research.

PARPs

Poly(ADP-ribose) polymerases — usually shortened to PARPs — participate in detecting and responding to DNA damage.

When DNA damage occurs, certain PARP enzymes consume NAD+ as part of the repair response.

CD38

CD38 is an enzyme involved in immune signalling and calcium regulation that is also a major consumer of NAD+.

Animal research has shown that CD38 activity can increase with age and contribute to age-related NAD+ depletion, although translating those findings directly into humans remains an active area of research. A recent Nature Reviews Endocrinology discussion highlights CD38 as an important component of the ageing-NAD relationship.

This gives us an interesting picture.

NAD+ sits at the intersection of:

energy production

DNA repair

cellular signalling

stress responses

and

metabolism.

That's why researchers care about it.

Does NAD+ Really Decline With Age?

You'll frequently see a statement online that sounds very definitive:

“NAD+ declines by 50% by middle age.”

The actual human evidence isn't that simple.

Animal studies provide substantial evidence of age-associated changes in NAD+ metabolism.

Human research has also identified age-related differences in NAD+ in some tissues.

But a major 2025 review in Nature Metabolism concluded that evidence for a consistent age-related decline in NAD+ in humans is much more limited and tissue-specific than is often portrayed.

Different tissues maintain separate NAD pools.

Blood NAD isn't necessarily telling us exactly what is happening inside skeletal muscle, brain, liver or other tissues.

Age isn't the only factor either.

NAD metabolism can potentially be influenced by:

metabolic health inflammation nutrient availability cellular stress activity NAD synthesis NAD-consuming enzymes.

So the scientifically accurate statement isn't:

“Everyone's NAD+ collapses as they age.”

It's:

Changes in NAD+ metabolism are associated with ageing, but the extent and significance of those changes in different human tissues are still being established.

If NAD+ Is So Important, Why Not Just Replace It?

This is where NAD research becomes particularly interesting.

NAD+ is a relatively large molecule, and simply putting more NAD+ into the body doesn't necessarily mean it will travel intact into every cell and increase the specific intracellular NAD pools researchers are interested in.

Our cells already possess pathways for making NAD+.

And much of the human research has therefore focused on providing the body with smaller molecules it can use as precursors.

Two have received particularly significant attention:

NR — nicotinamide riboside

and

NMN — nicotinamide mononucleotide.

Both can participate in pathways through which cells synthesise NAD+.

The question then becomes:

If we provide more precursor, can humans actually increase NAD+ availability?

Here, the answer is becoming clearer.

Can We Actually Increase NAD+ in Humans?

Yes — at least in certain compartments and under certain conditions.

Multiple human studies have demonstrated that NAD+ precursors can alter the NAD metabolome.

For example, a placebo-controlled study involving older men gave participants 1,000 mg of nicotinamide riboside daily for 21 days.

Researchers found that NR increased markers of the skeletal-muscle NAD+ metabolome.

Another randomised placebo-controlled trial involving 120 adults aged 60–80 found that an NR-containing intervention increased whole-blood NAD+ concentrations in a dose-dependent manner.

So we have reasonable evidence for an important first step:

NAD biology can be manipulated in humans.

But then comes the much bigger question.

Does Raising NAD+ Actually Make Humans Healthier?

This is where the story becomes considerably less certain.

Increasing a biomarker isn't the same as improving health.

Think about it this way:

If an intervention raises NAD+ by 50%, but the person doesn't become stronger, healthier, more metabolically resilient or less likely to develop disease, then increasing the number itself may have limited clinical relevance.

Human trials have produced mixed results.

In the older-men study, NR altered the muscle NAD metabolome and produced some transcriptomic changes associated with inflammatory pathways.

But it did not improve mitochondrial bioenergetics.

Another controlled study of obese and insulin-resistant men found that prolonged NR supplementation did not improve skeletal-muscle mitochondrial respiration, mitochondrial content or morphology.

A separate small study involving overweight or obese adults found changes in NAD-related metabolites and reported increases in fat-free mass and sleeping metabolic rate, but it involved only 13 participants and therefore needs cautious interpretation.

This is exactly why the 2025 Nature Metabolism review reached a cautious conclusion: NAD+ precursors can increase NAD-related metabolites, but human clinical trials have so far demonstrated limited and inconsistent efficacy for healthy ageing outcomes.

NAD+ & Cellular Energy: Does More Mean More Energy?

This is another area where language can be misleading.

Because NAD+ participates in energy metabolism, it's tempting to assume:

More NAD+ = more energy.

That's not how physiology works.

Cellular energy production depends on an entire network involving:

glucose and fatty acids,

oxygen availability,

mitochondria,

enzymes,

physical activity,

hormonal signalling,

nutritional status,

and many other factors.

NAD+ is an essential part of that machinery.

But increasing one component doesn't necessarily make the entire system run faster.

This may help explain why some studies successfully increase NAD-related metabolites without demonstrating dramatic improvements in mitochondrial function.

Biological necessity doesn't automatically mean supplementation produces additional benefit.

What About DNA Repair?

This is one of the most compelling aspects of NAD biology.

Our DNA is continuously exposed to damage.

Some comes from external sources such as ultraviolet radiation.

Some arises from normal cellular metabolism.

The body therefore maintains sophisticated DNA-damage detection and repair mechanisms.

Certain PARP enzymes use NAD+ while participating in these responses.

That creates an interesting relationship:

DNA damage can increase NAD+ consumption.

In preclinical models, excessive PARP activation can substantially deplete cellular NAD+.

This is one reason researchers are investigating whether maintaining NAD homeostasis could become relevant in conditions involving unusually high levels of DNA damage.

But once again:

NAD+ being required for DNA repair does not mean NAD+ supplementation has been proven to reverse DNA ageing in healthy humans.

Mechanism and clinical outcome are two different things.

NAD+, Sirtuins & The Longevity Connection

If you've followed longevity research, you've probably encountered sirtuins.

Sirtuins are sometimes called “longevity genes” or “longevity proteins”.

That's an oversimplification.

They are a family of enzymes involved in regulating numerous cellular processes, and importantly:

their activity requires NAD+.

This created an attractive scientific hypothesis.

If NAD+ availability changes with ageing, could this influence sirtuin activity and therefore some processes associated with cellular ageing?

Animal experiments have generated fascinating results around NAD metabolism, sirtuins and longevity.

But the leap from:

NAD+ → sirtuins → longevity pathways

to:

NAD+ supplementation makes humans live longer

has not been demonstrated.

There are currently no robust human clinical trials showing that raising NAD+ extends human lifespan.

The 2025 assessment of the field emphasises exactly this translational gap between strong preclinical biology and much less convincing clinical outcomes in otherwise healthy humans.

What About NAD+ IV Therapy?

This deserves its own section because NAD+ intravenous infusions have become increasingly visible in longevity and wellness clinics.

The marketing claims can be dramatic.

IV NAD+ is promoted for everything from:

energy,

mental clarity,

anti-ageing,

athletic recovery,

addiction,

and cellular rejuvenation.

The problem is that the clinical evidence supporting many of these claims is extremely limited.

Most of the better human evidence in the NAD field currently involves NAD precursors such as NR, not expensive intravenous NAD+ protocols.

There are also unanswered pharmacokinetic questions about how administered NAD+ is metabolised and how much intact extracellular NAD+ ultimately contributes to intracellular NAD pools in specific tissues.

So although IV administration may sound inherently more powerful than an oral precursor, route of administration doesn't substitute for evidence of clinical benefit.

This is an area where the marketing is currently much further ahead than the science.

NAD+ Isn't Really an “Anti-Ageing Molecule”

This might be the most important distinction in the whole article.

NAD+ is unquestionably important.

Without adequate NAD metabolism, cells cannot function normally.

But that doesn't automatically make NAD+ an anti-ageing treatment.

It's better understood as part of the fundamental machinery of cellular life.

Its connection with ageing exists because many of the processes in which it participates — mitochondrial metabolism, DNA repair, inflammation and cellular stress responses — also change as organisms age.

The interesting scientific question isn't:

“Does NAD+ reverse ageing?”

We don't have evidence that it does.

The better question is:

“Does altered NAD metabolism contribute to particular aspects of human ageing, and can modifying it meaningfully improve health?”

That's what researchers are still trying to establish.

Can We Support NAD+ Biology Naturally?

There's an irony in the huge commercial interest around NAD+.

Some of the most powerful interventions associated with healthy ageing already interact with the same metabolic systems researchers are studying.

Exercise

Physical activity creates metabolic demand and triggers adaptations throughout skeletal muscle and mitochondria.

Exercise also influences enzymes involved in NAD metabolism.

Sleep

Circadian biology and metabolism are deeply connected.

Sleep disruption alters glucose regulation, hormones, appetite and numerous aspects of cellular metabolism.

Nutrition

The body needs raw materials to synthesise NAD+.

Vitamin B3 compounds — including niacin and nicotinamide — contribute to NAD biosynthesis.

Severe vitamin B3 deficiency historically causes pellagra, illustrating just how essential NAD-related metabolism is to human health.

Metabolic Health

Obesity, insulin resistance, chronic inflammation and ageing can all interact with cellular metabolism.

Supporting overall metabolic health may therefore be considerably more important than chasing one isolated biomarker.

Once again, the body works as a network.

The Bigger Picture: Maintaining the Cellular Machinery

NAD+ is fascinating precisely because it isn't a miracle compound.

It's something much more fundamental.

Every moment we're alive, our cells must:

produce energy

repair damage

respond to stress

maintain their DNA

communicate

and

adapt to changing conditions.

NAD+ participates in all of those processes.

That makes it one of the most interesting molecules in modern ageing research.

And we now know that certain NAD+ precursors can alter NAD metabolism in humans.

What we don't yet know is whether increasing NAD+ in otherwise healthy people translates into substantial improvements in healthspan — or whether it can meaningfully slow biological ageing.

That's a much higher scientific bar.

And it's exactly why NAD+ deserves serious research rather than exaggerated claims.

NAD+ isn't proof that we've discovered how to reverse ageing.

It's evidence of how much we're beginning to understand about the cellular machinery involved in ageing.

And that may ultimately prove much more valuable.

Research. Understand. Explore.

Research & Further Reading

A 2025 review in Nature Metabolism provides one of the most useful current assessments of NAD+ precursor supplementation and human ageing. It concludes that evidence for universal age-related NAD+ decline in humans remains more limited than commonly claimed and that, although precursor supplementation can alter NAD metabolism, clinical benefits have so far been inconsistent.

Human research involving older men has demonstrated that nicotinamide riboside can augment the skeletal-muscle NAD+ metabolome, although this did not translate into improved mitochondrial bioenergetics during the short intervention.

Randomised research has also demonstrated increases in whole-blood NAD+ following an NR-containing intervention, providing evidence that NAD metabolism can be manipulated in humans.

Other controlled human research has found no improvement in skeletal-muscle mitochondrial respiration, content or morphology following NR supplementation, illustrating the important distinction between raising NAD-related biomarkers and demonstrating functional benefit.

Important Research Disclaimer

This article is provided for research and educational purposes only. It discusses published scientific research into NAD+, NAD metabolism, cellular ageing and NAD+ precursors.

NAD+ and its precursors are being investigated across numerous areas of human health, but many proposed anti-ageing, energy, cognitive and longevity benefits have not been established in robust human clinical trials.

Research involving oral NAD+ precursors should not automatically be extrapolated to intravenous NAD+ therapies or other routes of administration.

Nothing in this article constitutes medical advice, diagnosis or a recommendation to use NAD+, NR, NMN, intravenous NAD+ or any other supplement or treatment.

Better Body Lab | Research. Understand. Explore.