Medically reviewed by: Lenka Orlovská, PharmDr. — Pharmacy, Univerzita Karlova, Farmaceutická fakulta v Hradci Králové

Last reviewed: 2026-09-20

NAD+ (nicotinamide adenine dinucleotide) is a coenzyme present in every cell, where it carries electrons in energy metabolism and acts as a substrate for enzymes involved in DNA repair and cellular signalling. Its concentration falls with age in human tissue. That decline is the reason NAD+ precursors are studied — and it is a rationale for research, not a demonstrated intervention.

This article explains what NAD+ does, what is actually known about raising it, and how to tell a mechanistic argument from a clinical result. The distinction matters, because almost all content on this subject blurs it.

Key points

NAD+ is a coenzyme in energy metabolism and a substrate for sirtuins and PARP enzymes
Tissue NAD+ concentrations decline with age — this is well documented
Oral NAD+ itself is poorly absorbed, which is why precursors are used
Precursors reliably raise blood NAD+ in trials; downstream clinical outcomes remain unproven
Fasting and exercise influence NAD+ metabolism, though effect sizes in humans are modest
No health claim for NAD+ or its precursors appears on the EU Register

What NAD+ actually does

NAD+ has two distinct roles, and they are often conflated.

As a redox coenzyme. It cycles between NAD+ and NADH, carrying electrons through glycolysis, the citric acid cycle and oxidative phosphorylation. In this role it is recycled, not consumed.

As an enzyme substrate. Sirtuins and PARP enzymes cleave NAD+ as part of their activity, which means it is consumed. PARP enzymes are involved in DNA damage response; sirtuins are involved in a range of regulatory processes. This is the role that connects NAD+ to the ageing literature.

Why levels fall with age

Measurements in human tissue show NAD+ concentrations decrease with age. Two mechanisms are discussed: reduced synthesis, and increased consumption by enzymes such as PARPs and CD38 under conditions of accumulated cellular stress.

What this observation does not establish is direction. Whether declining NAD+ contributes to ageing, results from it, or both, is not settled by the correlation.

The precursors, and where the evidence stops

Because NAD+ taken orally is broken down before reaching cells, research uses precursors — principally nicotinamide riboside (NR) and nicotinamide mononucleotide (NMN), alongside plain nicotinamide and nicotinic acid.

Human trials consistently establish the first step: precursor supplementation raises blood NAD+ measurably and dose-dependently — from around 20% at low doses to well over 100% at high ones — typically within two weeks.

The second step is where the picture thins. Trials that measured functional outcomes — cognition, symptoms, physical performance — have largely not shown differences from placebo in generally healthy adults. Blood NAD+ rose; the outcome did not follow.

That is the honest state of the field, and anyone presenting NAD+ precursors as an established intervention is describing a hope rather than a finding.

Fasting, exercise and NAD+

Energy restriction and exercise both influence NAD+ metabolism, largely through changes in the NAD+/NADH ratio and in the activity of the enzymes that consume it.

Two cautions. Much of the detailed mechanistic work comes from animal models, where fasting protocols are far more extreme than anything a person would follow. And in humans the measurable changes in NAD+ from lifestyle interventions are modest.

Fasting and exercise remain sensible for reasons that have nothing to do with NAD+. Presenting them as NAD+ interventions overstates a small effect.

Autophagy — related, but a separate process

Autophagy is the cellular process that degrades and recycles damaged components. It is frequently discussed alongside NAD+ because both are influenced by energy status and both decline with age, and because sirtuins appear in both literatures.

They are connected, but they are not the same thing, and evidence about one does not transfer to the other. Articles that move between them without marking the transition are worth reading sceptically.

What EU law permits here

Under Regulation (EC) No 1924/2006, only health claims on the EU Register may be used. No claim relating to NAD+, NR or NMN and ageing, longevity or cellular renewal appears on that Register.

Regulatory status differs by substance as well: NR chloride was authorised as a novel food by Commission Implementing Regulation (EU) 2020/16, as a source of niacin in food supplements. NMN is not authorised in the EU — EFSA has issued a positive safety opinion, but the Commission has not yet adopted the implementing act that would allow it on the market. Authorisation is a safety assessment — it is not evidence of benefit and it is not a health claim.

Frequently asked questions

Can I take NAD+ directly?
Oral NAD+ is poorly absorbed, which is why research uses precursors such as NR instead.

Does raising NAD+ slow ageing?
No trial has demonstrated that in humans. Trials show blood NAD+ rises; functional outcomes have generally not differed from placebo in healthy adults.

NR or NMN?
They differ in EU regulatory status and in the volume of published human data. NR has more completed trials and holds novel food authorisation in the EU.

Does fasting raise NAD+?
Energy restriction influences NAD+ metabolism, though measured changes in humans are modest and much of the mechanistic detail comes from animal work.

How long before blood NAD+ changes?
Trials typically measure increases within two to eight weeks of daily supplementation.

Unveiling the Mystery of NAD: The Key to Cellular Renewal and Longevity