Why NAD+ Declines With Age — And How Strong the Evidence Really Is

The claim everyone repeats

Open almost any NAD+ supplement page and you will meet the same sentence: levels fall by half every twenty years, so by forty you are running on a fraction of the cellular energy you had at twenty. It is a clean, alarming number. It is also, as far as anyone can trace, unsourced.

We went looking for the primary measurement behind it and could not find one. No human study reports a halving of NAD+ per twenty-year interval. That does not mean NAD+ is stable — it does not. It means the most quotable claim in this category is the one with the weakest footing, and that distinction matters if you are trying to decide what to put in your body.

What the human data actually shows

Human NAD+ is hard to measure. It degrades quickly in a blood draw, it sits at very different concentrations in different tissues, and you cannot ethically punch a hole in someone's liver for a research sample. That is why the published human dataset is built mostly from two tissues: skin and plasma.

Skin tissue: a real but modest signal

The most frequently cited human study measured NAD+ directly in skin samples from 49 people and found a negative correlation between NAD+ and age, strongest in men (r = −0.706, p = 0.001) [1]. This is a genuine human measurement, not an animal extrapolation. Note what it does not contain: the paper never reports a percentage decline per decade, and the study was not designed to establish one.

Plasma: a mixed picture

Plasma tells a subtler story. A 2019 study found that plasma NAD+, NADP+ and NAAD all decline with age, while other metabolites in the same pathway — including NMN and niacin — did not change significantly [2]. In other words, the direction is consistent, but the parts of the NAD+ metabolome do not move together. Any article that treats "NAD+ levels" as a single dial is oversimplifying a system with several independent compartments.

Why no honest percentage exists

The cleanest statement of the state of the field comes from a 2025 review in Nature Metabolism: age-related NAD+ decline "has been consistently observed only in a limited number of studies," human tissue data "remains sparse," and human trials to date have shown "limited efficacy" [3]. A 2026 systematic review in Ageing Research Reviews, pooling 113 intervention studies, reached a compatible conclusion from the other direction: precursors raise NAD+ markers reliably, but that rise has not translated into consistent clinical benefit [4].

The mechanism behind the decline

If the measurement is uncertain, the biology is at least well described. NAD+ sits at the center of two of the busiest reactions in the cell: it carries electrons in energy-yielding metabolism, and it is consumed as a substrate by enzymes that read the state of the cell — the sirtuins and the PARPs [5].

It is also the reason the longevity aisle reads the way it does. The marketing promise is that you will feel younger; the underlying evidence is a negative correlation measured in skin samples and a plasma metabolome that moves in more than one direction. Nicotinamide mononucleotide, or NMN, and nicotinamide riboside, or NR, are the two precursors used in essentially all of it.

NAMPT is the bottleneck

Mammalian cells recycle NAD+ through the salvage pathway, and the rate-limiting step in that pathway is an enzyme called NAMPT. NAMPT activity itself declines with age, and because NAMPT is also under circadian control, the pathway has a daily rhythm on top of a slow downward trend [6]. This is why a supplement supplying a precursor — the raw material upstream of NAMPT — is a mechanistically sensible intervention rather than an arbitrary one.

Two different kinds of loss

It helps to separate two things that get blurred together. The first is reduced synthesis: less NAMPT-driven recycling. The second is increased consumption: inflammatory signaling raises the activity of CD38, an enzyme that degrades NAD+, so a chronically inflamed tissue burns through the same molecule faster [5]. A precursor supplement addresses the supply side. It does not switch off the demand side. That asymmetry is the reason no responsible article should promise you a restored twenty-year-old NAD+ profile.

What to look for in a supplement

Because NAD+ itself is a large, charged dinucleotide, taking it by mouth does not deliver intact NAD+ to your tissues in any meaningful quantity. What reaches the salvage pathway is a precursor. In practice that means the useful question is not how much NAD+ is in this capsule, but which precursor, at what dose, in which physical form [7].

You will see the phrase NAD+ booster attached to 1000mg capsules, to liposomal liquids and to sublingual drops, with the format presented as the innovation. It usually is not. A pure, clearly named precursor with a stated milligram amount on the label tells you more than any delivery claim, because dose is the one variable the human trials actually varied.

What the research shows — by evidence grade

It is worth being explicit about how differently these evidence types should be weighted.

• Observational human data (moderate). Skin and plasma studies establish that NAD+ is negatively associated with age [1][2]. Correlation, with limited sample sizes, no causal inference.
• Randomised human trials of precursors (good safety, mixed outcomes). Oral nicotinamide riboside has repeatedly been shown to raise circulating NAD+ in a dose-dependent way, and has been well tolerated across trials up to 12 weeks [8][9]. Trial endpoints beyond the biomarker have generally not moved: mitochondrial respiration in muscle did not change [10], and insulin sensitivity did not improve [8].
• Systematic reviews (the sobering layer). Pooled across 113 studies, the signal is a reliable biomarker increase without a consistent clinical payoff — and intravenous NAD+ has no qualifying outcome trial behind it at all [4].

Reading those three tiers in sequence is the only way to use this literature honestly. The first tier tells you the problem is real. The second tells you the intervention is safe and does something measurable. The third tells you not to overclaim what that something is.

What to do about it

1. Sort sleep before supplements. NAMPT is circadian, so a stable daily rhythm is upstream of the whole pathway. If your bedtime swings by three hours, no capsule outruns that.
2. Train, but recover. Contracting muscle is one of the most reliable physiological stimuli for NAD+ turnover, and it also improves insulin sensitivity — the outcome a precursor alone did not move in trials.
3. Take the inflammation side seriously. Since CD38 activity rises with inflammatory load, the supply-side lever works better when the demand side is not being driven up. That is dietary, not pharmaceutical.
4. If you supplement, choose a precursor and know its dose. Look for a clearly stated precursor and a milligram figure on the label, not a proprietary blend total.

When this is not a nutrition question

Persistent fatigue, unexplained weight change, brain fog that interferes with work, or a sleep problem that has lasted months are reasons to see a clinician. Fatigue is a symptom with a long differential, and NAD+ is not a diagnostic category. If you are pregnant or nursing, or taking medication, treat any supplement decision as one to raise with your healthcare provider first. Women and men metabolize and clear these compounds differently enough that a personalised discussion beats a generic protocol.

How our NAD+ formula maps onto this

Fmlave NAD+ 120 capsules is built around 500 mg of nicotinamide riboside per serving — a precursor chosen deliberately because it is the form with the deepest published human trial record, including dose-dependent whole-blood NAD+ increases [9]. It is paired with resveratrol, quercetin, fisetin and a 30:1 shilajit extract, and it is third-party tested with the certificate of analysis available on request.

It is a 12-in-1 complex, vegan, non-GMO and free of gluten and soy. What it is not is a way to return your NAD+ profile to what it was at twenty — because, as the data above shows, nobody can honestly claim that. What a well-dosed precursor can do is supply the raw material for a pathway that becomes rate-limited with age. That is a modest claim. We would rather make a modest claim we can support.