NAD+ and Ageing: What Does the Science Actually Say?

Few molecules have generated as much interest within contemporary ageing research as nicotinamide adenine dinucleotide (NAD+).

NAD+ is frequently discussed alongside terms such as mitochondrial health, cellular ageing, longevity and DNA repair. This has inevitably led to increasingly ambitious claims about NAD+ supplementation.

But what does the science actually show?

Understanding the answer requires distinguishing between three things: the established biological functions of NAD+, findings from laboratory and animal research, and evidence that an intervention produces meaningful outcomes in humans.

What Is NAD+?

NAD+ is an essential coenzyme present throughout the human body.

It exists in an oxidised form, NAD+, and a reduced form, NADH. The ability of these molecules to accept and donate electrons allows the NAD+/NADH system to participate in numerous oxidation-reduction, or redox, reactions.

This is particularly important in metabolism.

NAD+ participates in glycolysis, the tricarboxylic acid cycle — also known as the Krebs or citric acid cycle — and mitochondrial oxidative metabolism.

NADH generated during metabolism can subsequently donate electrons to the mitochondrial electron transport chain, contributing to the processes through which ATP is generated.

NAD+ therefore plays a fundamental role in normal cellular physiology.

Why Are Scientists Interested in NAD+ and Ageing?

NAD+ is interesting to ageing researchers for reasons extending beyond its traditional role as an electron carrier.

It is also required by enzymes involved in cellular signalling and maintenance.

Two frequently discussed examples are sirtuins and PARPs.

NAD+ and Sirtuins

Sirtuins are a family of NAD+-dependent enzymes.

They influence the activity of various proteins through deacylation reactions and have been investigated in relation to metabolism, cellular stress responses, mitochondrial biology and ageing.

Because their enzymatic activity requires NAD+, changes in cellular NAD+ availability have the potential to influence these signalling pathways.

Much of the excitement surrounding sirtuins and longevity, however, originated from experimental organisms and preclinical models.

Human ageing is substantially more complex.

NAD+ and PARPs

Poly(ADP-ribose) polymerases, or PARPs, are another family of NAD+-consuming enzymes.

Certain PARPs respond to DNA damage and participate in cellular DNA-repair signalling.

Because DNA damage accumulates through multiple mechanisms over a lifetime, interactions between NAD+ metabolism, PARP activity and cellular maintenance have become another important area of ageing research.

Again, precision of language matters.

Saying “NAD+ is involved in biochemical pathways associated with DNA repair” is scientifically different from saying “an NAD+ drip repairs your DNA.”

The former describes molecular biology.

The latter is a clinical efficacy claim requiring evidence that IV NAD+ actually produces that outcome in humans.

Does NAD+ Decline with Age?

This question is more complicated than many online descriptions suggest.

Preclinical studies have demonstrated age-associated alterations in NAD+ metabolism, and some human studies have reported lower NAD+ concentrations with increasing age in particular tissues.

But NAD+ is not distributed uniformly throughout the body.

The concentration and metabolism of NAD+ may differ between blood, skeletal muscle, liver, brain, adipose tissue and other compartments.

Different studies also use different analytical techniques, participant populations and biological samples.

Consequently, we should be cautious about describing a universal decline in NAD+ as though every person's NAD+ level simply falls by a predictable percentage each decade.

A major scientific review published in Nature Metabolism in 2025 concluded that evidence for an age-related decline in human NAD+ has been consistently demonstrated in only a limited number of studies.

The authors also emphasised that our understanding of NAD+ dynamics across human tissues remains incomplete.

NAD+ and Mitochondrial Function

Mitochondria play an essential role in oxidative metabolism and ATP generation.

NADH supplies electrons to Complex I of the mitochondrial respiratory chain. These electrons move through a series of respiratory complexes, contributing to the proton gradient required for ATP synthesis.

Maintaining appropriate NAD+/NADH balance is therefore fundamental to normal cellular metabolism.

Ageing is also associated with complex changes in mitochondrial function.

This overlap has contributed to considerable interest in whether manipulating NAD+ metabolism could influence aspects of age-associated physiology.

Laboratory research has produced intriguing results.

But biological plausibility is not synonymous with demonstrated clinical effectiveness.

What About NAD+ Precursors Such as NMN and NR?

Much of the human research often discussed in relation to NAD+ supplementation has actually investigated NAD+ precursors, rather than intravenous NAD+ itself.

Two commonly studied compounds are:

• Nicotinamide riboside (NR)

• Nicotinamide mononucleotide (NMN)

These compounds participate in biochemical pathways through which the body can synthesise NAD+.

Human trials have demonstrated that NAD+-related metabolites can be altered through some precursor interventions.

The much more difficult question is whether those biochemical changes consistently translate into meaningful improvements in health, physical function, cognition or longevity.

So far, results have been considerably less dramatic than some headlines imply.

Recent scientific reviews have highlighted the difference between the promising effects seen in preclinical models and the relatively limited clinical efficacy demonstrated in humans.

What About Intravenous NAD+?

IV NAD+ represents another distinct question.

Intravenous administration introduces NAD+ into the systemic circulation without requiring gastrointestinal absorption.

However, NAD+ biology does not stop at the bloodstream.

Researchers must consider what happens to extracellular NAD+, its metabolism and breakdown products, transport across cellular membranes, tissue-specific metabolism and whether administration ultimately produces clinically meaningful changes within relevant tissues.

These are important pharmacological and physiological questions.

Direct human research specifically examining IV NAD+ remains limited compared with the much larger body of fundamental NAD+ research.

It is therefore important not to use studies involving NR, NMN, animal models or isolated cells as though they prove the clinical effects of an NAD+ IV infusion.

Can NAD+ Slow Ageing?

At present, there is not sufficient evidence to state that NAD+ IV therapy slows human ageing.

Nor is there established evidence that NAD+ IV therapy extends human lifespan.

Ageing is an extraordinarily complex biological phenomenon involving genomic changes, epigenetic regulation, mitochondrial function, protein homeostasis, cellular senescence, inflammation, stem-cell function, metabolism and numerous other interacting processes.

It is unlikely that human ageing can be reduced to the concentration of a single molecule.

That does not make NAD+ research unimportant.

Quite the opposite: understanding NAD+ metabolism may contribute substantially to our broader understanding of human physiology and ageing.

But responsible interpretation requires recognising the boundary between interesting science and established medicine.

Why Scientific Language Matters

One of the problems surrounding emerging wellness therapies is that genuine scientific terminology can inadvertently be used to make an unproven treatment sound clinically established.

“Mitochondrial function”, “DNA repair”, “cellular energy” and “sirtuin activation” are legitimate scientific concepts.

Their relevance to NAD+ biology does not automatically mean that administering NAD+ intravenously will improve all of them in a way that produces measurable health benefits.

For patients, understanding this distinction is valuable.

It allows NAD+ therapy to be considered within its actual scientific context rather than through exaggerated promises.

A Measured Approach to NAD+ Therapy

At New Body Clinic in Beaconsfield, our approach is to distinguish between what is established about NAD+ as a biological molecule and what remains under investigation regarding NAD+ as a therapeutic intervention.

NAD+ is unquestionably important to cellular metabolism.

Its interactions with mitochondrial metabolism, redox biology, sirtuins, PARPs and other cellular pathways make it an important subject of contemporary biomedical research.

Whether manipulating NAD+ metabolism ultimately produces significant effects on human healthspan or ageing remains an active area of scientific investigation.

Patients considering NAD+ IV therapy should therefore be given balanced information and an individual clinical assessment rather than promises of rejuvenation or extended longevity.

Frequently Asked Questions

Does NAD+ decrease as you get older?

Some human studies have observed age-associated reductions in NAD+ in particular tissues, but the evidence is not consistent across all tissues and populations. Human NAD+ metabolism during ageing remains an active research area.

Does NAD+ reverse ageing?

There is currently insufficient clinical evidence to claim that NAD+ supplementation or IV NAD+ reverses human ageing.

What are sirtuins?

Sirtuins are NAD+-dependent enzymes involved in several cellular processes, including metabolic regulation and responses to cellular stress. Their dependence on NAD+ is one reason NAD+ metabolism has attracted interest in ageing research.

Is NAD+ involved in DNA repair?

NAD+ is used by enzymes including PARPs that participate in DNA damage-response and repair pathways. This biochemical relationship should not be interpreted as evidence that an NAD+ IV infusion has been proven to repair DNA in patients.

Is NAD+ IV therapy the same as taking NMN or NR?

No. NR and NMN are NAD+ precursors, whereas an NAD+ infusion administers NAD+ intravenously. Findings from studies of one approach cannot automatically be applied to another.