NAD+ vs Glutathione: What the Human Studies Actually Show

By Peremis Editorial Team · Updated August 3, 2026· 17 min read

Last updated: 31 July 2026 · Reviewed against primary sources by the Peremis Editorial Team

What changed in this update: we removed several claims that could not be traced to any published study, added the largest human NAD+ dataset ever collected, added the null trial results the supplement industry rarely quotes, and replaced the vague marketing numbers with the actual figures from the papers.

Search either of these molecules and you will meet the same two promises within about thirty seconds. NAD+ is the fuel that keeps your cells young. Glutathione is the master antioxidant that clears the damage. Take both and you get energy, clarity, better skin, slower ageing.

That is the pitch. This guide is about what the actual human studies say, which turns out to be a much more interesting story, and a considerably less flattering one for the supplement aisle.

The short answer: NAD+ and glutathione do genuinely different jobs. NAD+ is the coenzyme your cells use to convert food into energy and to run DNA repair. Glutathione is the antioxidant that neutralises the damage that energy production creates. They are biochemically linked, because NAD+ is the raw material for NADPH, which is what recycles spent glutathione. But no published human trial has ever tested the two together, and the strongest evidence for either one supplement is weaker than the marketing suggests.

What is NAD+ and what does it actually do?

NAD+, short for nicotinamide adenine dinucleotide, is a coenzyme found in every living cell. Its job is to carry electrons. When your cells break down glucose or fat, NAD+ picks up the electrons released and delivers them to the mitochondria, where they drive the production of ATP, the molecule your body actually spends as energy.

NAD+ is also the fuel for two families of enzymes that get a lot of research attention. Sirtuins, which are involved in how cells respond to stress and how genes are switched on and off. And PARPs, which are recruited when DNA needs repairing. Both consume NAD+ as they work, which is why heavy DNA damage can drain the cellular NAD+ pool.

So far, so uncontroversial. The controversy starts with the next sentence, which almost every NAD+ product on the market makes.

Does NAD+ really decline with age?

This is where the evidence gets messy, and it is worth understanding because the entire NAD+ supplement category rests on it.

Tissue measured	What the study found	Source
Skin	Strong negative correlation with age across 49 people aged 0 to 77	Massudi, PLoS ONE, 2012
Brain	Roughly 10 to 20 percent lower between the twenties and the sixties	Reviewed in Nutrients, 2022
Liver	About 30 percent lower in older samples, though only six people per group	Zhou, Br J Pharmacol, 2016
Skeletal muscle	Lower in older adults, but closely tied to daily step count. Active older adults sat near young levels.	Janssens, Nature Aging, 2022
Whole blood	No significant overall decline with age across 1,518 people. Only men aged 60 and over showed a drop. No age trend at all in women.	Yang, Front Endocrinol, 2022

Read that last row again, because it is the single most important line on this page. The largest human NAD+ dataset ever assembled found no overall age related decline in blood. A 2022 review in Nutrients looked at the whole literature and concluded that despite systematic claims of overall changes in NAD+ with ageing, the evidence supporting those claims is very limited.

There is a further problem. Every human NAD+ study is cross sectional. Nobody has followed the same people over decades. So what looks like a decline with age could partly be a difference between generations, or between people who move a lot and people who do not. The muscle study above hints strongly at the second explanation.

The claim you should stop repeating

You will see it everywhere: by fifty you have half the NAD+ you had at twenty. We could not find a single human study reporting anything like that. The real measured numbers are around 10 to 20 percent in brain and around 30 percent in liver, from small samples, with zero decline in the largest blood dataset. The "half by fifty" line comes from marketing, not from a journal.

What is glutathione and why is it called the master antioxidant?

Glutathione is a small protein made of three amino acids: cysteine, glutamine and glycine. Your body makes it. You do not have to eat it, and in fact your liver is producing it continuously right now.

Its main role is to donate electrons to unstable molecules called free radicals, neutralising them before they damage DNA, proteins or cell membranes. It also supports the liver's normal processing of compounds the body wants to clear, and it regenerates other antioxidants like vitamin C and vitamin E after they have been used up.

The "master antioxidant" nickname is not marketing. Glutathione is present in essentially every cell, usually at higher concentrations than any other antioxidant, and it sits at the centre of the network rather than at the edge of it.

Does glutathione decline with age?

Here the evidence is cleaner than for NAD+, though the samples are tiny. A study in the American Journal of Clinical Nutrition compared eight healthy older adults with eight younger ones and found red blood cell glutathione was about 46 percent lower in the older group. More importantly, the rate at which they were making new glutathione was 68 percent slower.

That second number matters more than the first. The problem was not that older bodies were burning through glutathione faster. It was that they had slowed down building it. Eight people per group is a small study and should be treated as a starting point rather than a settled fact, but the finding has held up directionally in later work.

NAD+ vs glutathione: the honest comparison

Factor	NAD+	Glutathione
What it is	A coenzyme that carries electrons	A three amino acid peptide antioxidant
Primary job	Energy production, DNA repair, sirtuin activity	Neutralising free radicals, supporting normal liver clearance
Made from	Vitamin B3 and its relatives, plus salvage recycling	Cysteine, glutamine and glycine
Evidence it declines with age	Mixed. Real in some tissues, absent in the largest blood study.	Consistent, but from very small samples
Can a supplement raise levels?	Yes, clearly and dose dependently, using NR or NMN	Not from a single dose. Yes over months of daily use.
Does raising it change how you function?	Largely no, in trials to date	Barely studied for functional outcomes
Best supported approach	Exercise and adequate B3 from food	Supplying the building blocks, especially cysteine and glycine

How the two systems are actually connected

You will read that NAD+ boosts glutathione production. That is close, but it describes the wrong process.

Roughly a tenth of cellular NAD+ gets converted into NADP+, which is then reduced to NADPH. NADPH is the reducing power that an enzyme called glutathione reductase uses to convert spent, oxidised glutathione back into its active form. So NAD+ does not build new glutathione. It funds the recycling of the glutathione you already have.

Building new glutathione runs through completely different enzymes and depends on ATP and on how much cysteine is available. There is some cell culture work suggesting a sirtuin driven link to the synthesis pathway too, but that was done in rat cells, not people.

The recycling relationship is real biochemistry. It is not, on its own, evidence that taking both as supplements does anything. Those are two different questions and the supplement industry routinely blurs them.

What happens when people actually take these supplements?

This is the part that gets skipped, so we will spend some time on it.

NAD+ precursors: the levels go up

You cannot absorb NAD+ itself as a molecule, so products use precursors, usually nicotinamide riboside (NR) or nicotinamide mononucleotide (NMN). These work. In a trial of 140 healthy overweight adults published in Scientific Reports, whole blood NAD+ rose 22 percent at 100 mg, 51 percent at 300 mg and 142 percent at 1,000 mg of NR per day, and stayed elevated through eight weeks.

That is a clean, dose dependent result. The supplements do what they say on the tin.

And then nothing much happens

In that same 140 person trial, despite blood NAD+ more than doubling, there was no change in resting energy expenditure, blood pressure, heart rate, body weight, LDL cholesterol or inflammatory markers.

A separate placebo controlled crossover study in Cell Reports gave twelve older men 1 g of NR daily for three weeks. It raised the NAD+ metabolome in muscle. It did not change mitochondrial bioenergetics.

The clearest verdict comes from a 2025 meta analysis in the Journal of Cachexia, Sarcopenia and Muscle pooling ten randomised trials of NMN and NR in adults averaging over sixty. No significant effect on muscle index, grip strength on either side, gait speed or the five times chair stand test. Every p value above 0.14. The authors' conclusion was that current evidence does not support NMN and NR supplementation for preserving muscle mass and function in this group.

There are positive findings. A ten week trial in Science in 2021 found improved insulin sensitivity in postmenopausal women with prediabetes on 250 mg of NMN, though that paper drew a published formal challenge to its interpretation. A small Japanese trial found modest gait speed and grip improvements. Neither is enough to override a ten trial meta analysis.

Oral glutathione: the timing problem

In 1992, researchers gave seven volunteers a single three gram oral dose of glutathione and watched plasma levels for four and a half hours. Nothing happened. Their published conclusion in the European Journal of Clinical Pharmacology was blunt: it is not possible to increase circulating glutathione to a clinically beneficial extent by the oral administration of a single dose of 3 g of glutathione.

That result stood for two decades and is still the reason many clinicians are sceptical of oral glutathione.

Then in 2015 a six month randomised trial in the European Journal of Nutrition put 54 adults on 250 mg or 1,000 mg of standard oral glutathione daily. Body stores rose meaningfully: about 17 percent in blood at the low dose, 30 to 35 percent in red cells and plasma at the high dose, and 260 percent in cheek cells. Every measure returned to baseline within a month of stopping.

So both findings are true. A single dose does essentially nothing. Daily use over months raises stores, most likely because the body breaks the peptide down and reuses the amino acids rather than absorbing it whole.

Is liposomal glutathione worth the premium?

You will see claims that liposomal delivery is five times better absorbed. We could not find any study producing that number.

What exists is thin and inconsistent. A 2018 trial of liposomal glutathione in twelve people raised body stores, but it had no comparison arm, so it cannot support any ratio at all. A randomised crossover trial published in Antioxidants in 2026 did run a direct head to head and found a micellar formulation outperformed standard glutathione, while the liposomal arm did not differ significantly from standard. Meanwhile a 2024 meta analysis pooling three trials found oral glutathione did not significantly raise red cell or plasma glutathione at all.

The honest summary: liposomal may help, the studies are small, at least one direct comparison found no advantage, and a specific multiple like five times is not supportable by anything published. For the full breakdown, read our head to head look at glutathione forms.

The combination claim, and why we removed it

An earlier version of this article cited a 2026 study in the Journal of Clinical Medicine reporting that NAD+ and glutathione together beat either alone in adults over fifty.

We went looking for that paper. It does not exist. There is no such trial in that journal, in PubMed indexed literature, or registered on ClinicalTrials.gov. We have removed the citation and we are flagging it here rather than quietly deleting it, because a fabricated reference is exactly the kind of thing that should be corrected in public.

The accurate statement is this. No published human trial has tested an NAD+ precursor and glutathione together. The biochemical rationale is genuine. The clinical evidence is absent. Anyone selling you the combination on the strength of a study is selling you something that has not been run.

What has the strongest evidence in this space?

Not NAD+ precursors, and not glutathione capsules. It is a combination of two cheap amino acids.

GlyNAC is glycine plus N acetylcysteine, the two rate limiting building blocks for making glutathione. Rather than trying to deliver the finished molecule past your stomach acid, it hands your cells the raw materials and lets them build it themselves.

A randomised, double blind, placebo controlled trial published in the Journals of Gerontology in 2023 ran sixteen weeks in older adults. Muscle glutathione rose 164 percent. A marker of oxidative damage fell 72 percent. Grip strength, chair rise time, gait speed and fat oxidation all improved, and systolic blood pressure fell by around 7.6 mmHg.

Now the caveat, and it is a big one. That trial had twelve people per arm, ran at a single centre, and came from one research group. It has not been independently replicated. Effect sizes that large from groups of twelve should be treated as a reason to run a bigger study, not as a settled result.

Peremis does not sell NAD+ precursors, glutathione or GlyNAC, and we are not going to pretend otherwise to sell you something adjacent. If this article is useful to you, the thing we would rather you take from it is the habit of checking claims. Start with our guide to reading a supplement label without getting fooled, then read our honest breakdown of what detox marketing gets wrong about your liver.

What actually works for the things people take these for

Most people arrive at NAD+ and glutathione because they are tired, foggy, or feel like recovery takes longer than it used to. Here is where the evidence is stronger.

Goal	Better supported approach	Why
Raise muscle NAD+	Regular physical activity	Muscle NAD+ tracked daily step count closely, and trained older adults sat near young levels
Support glutathione production	Adequate protein, especially cysteine rich foods, plus glycine	Cysteine availability is the rate limiting step in synthesis
Persistent tiredness	Rule out iron, B12, thyroid and sleep problems first	These are common, testable and treatable. No supplement substitutes for finding the cause.
Lower oxidative stress	Sleep, less alcohol, a plant heavy diet	Alcohol in particular depletes glutathione rapidly, especially in the liver
Everyday liver support	Drink less, and be careful with high dose botanicals	Reducing the load matters more than adding something on top

If tiredness is your main reason for reading this, our guides on the real reasons you are always tired and the difference between tired and depleted cover the causes worth ruling out first. If it is mental clarity, start with what actually causes brain fog.

Safety and regulatory status

Short term safety looks reassuring for all three. A four week trial of 3,000 mg of NR a day recorded 42 adverse events across twenty people, all graded mild, with a similar rate in the placebo group. A 2025 meta analysis of NMN across 383 participants found no increase in overall, serious or withdrawal related adverse events, and no rise in liver enzymes. Six months of oral glutathione at up to 1,000 mg a day produced no adverse effects attributed to treatment.

What nobody has is long term data. There is no multi year trial of any of these in healthy adults. That is not a reason for alarm, but it is a reason to be honest about what is unknown.

One regulatory note that dates a lot of older content. NMN was effectively blocked from the US supplement market for several years after it entered drug investigation. In September 2025 the FDA reversed that position and found NMN is not excluded from the dietary supplement definition. It still requires a new dietary ingredient notification before marketing, so the situation is not fully settled.

Frequently asked questions

Should I take NAD+ or glutathione?

Neither has strong evidence of a functional benefit in healthy adults. NAD+ precursors reliably raise NAD+ levels but a ten trial meta analysis found no effect on strength or walking speed. Oral glutathione raises body stores over months but has barely been tested for outcomes people actually notice. Exercise and adequate protein are better supported starting points.

Can you take NAD+ and glutathione together?

There is no known interaction and no safety signal against it, but there is also no published human trial testing the combination. The biochemical rationale is real, since NAD+ supplies the NADPH that recycles glutathione. Rationale is not evidence. Anyone claiming a proven combined benefit is describing a study that has not been run.

Does NAD+ really drop by half by age fifty?

No human study supports that figure. Measured declines are roughly 10 to 20 percent in brain tissue and around 30 percent in liver, from small samples. The largest study, covering 1,518 people, found no significant overall decline in blood NAD+ with age. The half by fifty claim comes from marketing rather than published research.

Is liposomal glutathione better than regular glutathione?

Possibly, but the evidence is thin and conflicting. One randomised crossover trial found a micellar form outperformed standard glutathione while the liposomal arm showed no significant advantage. A pooled analysis of three trials found oral glutathione did not significantly raise blood levels at all. Claims of five times better absorption have no published source.

What foods support glutathione levels?

Foods supplying the building blocks help most. Cysteine rich options include eggs, poultry, fish, yoghurt and sunflower seeds. Glycine is abundant in collagen rich foods and gelatin. Sulfur rich vegetables such as broccoli, cauliflower, garlic and onions support the pathway, and selenium from Brazil nuts and fish helps the recycling enzymes work.

Does NMN or NR give you more energy?

They raise blood NAD+ substantially, by around 142 percent at 1,000 mg of NR. In the trial that measured it, that increase produced no change in resting energy expenditure, blood pressure, weight or inflammatory markers over eight weeks. Subjective energy is hard to measure and easily influenced by expectation, so treat personal reports cautiously.

Is GlyNAC better than a glutathione supplement?

It has better evidence, though from very small studies. GlyNAC supplies glycine and N acetylcysteine so your cells build glutathione themselves. The only placebo controlled trial measuring strength and walking speed used GlyNAC, but it enrolled twelve people per group at one centre and has not been independently replicated.

Are these supplements safe?

Short term data look reassuring. High dose nicotinamide riboside produced only mild adverse events over four weeks, NMN showed no increase in adverse events across 383 participants, and six months of oral glutathione was well tolerated. No multi year trials exist in healthy adults. Speak with your provider before starting anything, especially alongside medication.

The bottom line

NAD+ and glutathione are both real, both important, and both genuinely central to how your cells work. None of that is in question.

What is in question is whether swallowing them, or their precursors, changes anything you would notice. On the current evidence, NAD+ precursors reliably move a number in your blood and reliably fail to move anything you can feel. Oral glutathione raises stores if you take it daily for months. And the combination that gets marketed hardest has never been tested in a single human trial.

That is not a reason to write off the whole field. NAD+ biology is one of the more interesting areas in ageing research and the trials are getting better. It is a reason to be sceptical of anything sold to you today on the strength of tomorrow's evidence.

Here is the useful habit. Next time a supplement promises a mechanism, ask a second question: has anyone tested whether that mechanism produces an outcome? The gap between those two things is where most of the money in this industry lives.

About this guide. Written by the Peremis Editorial Team. Every study referenced here was read at source rather than through a summary, and each claim links to the original paper. Where a previously published claim could not be traced to any real study, we removed it and said so. Peremis does not sell NAD+ precursors, glutathione or GlyNAC, and we have no commercial interest in your conclusion. We make no medical claims and we do not present supplements as a replacement for medical care.

These statements have not been evaluated by the Food and Drug Administration. Dietary supplements are not intended to diagnose, treat, cure, or prevent any disease. Always consult a licensed healthcare provider before starting a new supplement, especially if you are pregnant, nursing, taking medication, or have an existing health condition.