If you follow longevity science, you've heard of NAD+ (nicotinamide adenine dinucleotide). In the space of a few years it's gone from a biochemistry term to something people spend real money chasing — IV drips, precursor supplements like NMN and NR, entire protocols built around one molecule.
The part that gets skipped over is what happens after you swallow it. NAD+ itself can't be absorbed intact, precursor supplements have to survive digestion and the liver before they're useful, and even once inside the body, an enzyme actively hunts down and destroys the very molecule you're trying to build. None of that makes NAD+ restoration a dead end — the underlying biology is genuinely well studied. It does mean "take a bigger dose of raw powder" is a weaker strategy than the marketing suggests.
The Biological Currency of Youth
Start with mitochondria, the power plants inside your cells. They convert food into ATP, the energy currency your body actually spends — but they can't do it without NAD+, which acts as the shuttle that moves electrons through the process. No NAD+, no ATP production.
NAD+ has a second job that matters just as much for aging specifically: it's the required fuel for sirtuins, a family of proteins involved in DNA repair, inflammation control, and keeping cells from tipping into senescence. Sirtuins, PARPs (separate DNA-repair enzymes), and CD38 all draw from the same NAD+ pool, which is part of why demand for it doesn't ease up as supply declines.
And supply does decline: NAD+ levels fall by an estimated 50 percent or more between early adulthood and middle age, across tissues, in humans and in every model organism it's been measured in. That drop is a genuine, well-replicated finding — it's the "why" behind NAD+ research, and it isn't seriously disputed. The more contested territory is what to actually do about it.
The Absorption Bottleneck Is Real — But Not the Whole Story
NAD+ itself is a non-starter as a supplement; it's too large and chemically unstable to cross the gut wall intact. That's why the field turned to smaller precursors — nicotinamide mononucleotide (NMN) and nicotinamide riboside (NR) — that the body can convert into NAD+ once absorbed.
Oral NMN does face a real first-pass problem. Liver enzymes, mainly CD73 and NNMT, can convert a large share of it — some estimates put it at 70 to 90 percent — into nicotinamide (a form of vitamin B3) before much of it reaches systemic circulation.
Where the standard telling oversimplifies is what happens next. Nicotinamide isn't a dead end; it's the direct input for the salvage pathway, the same route your cells use to recycle NAD+ under ordinary circumstances via the enzyme NAMPT. Getting converted to nicotinamide in the liver isn't the supplement failing — it's the molecule being rerouted onto the pathway your body already runs NAD+ synthesis through by default. Separately, there's genuine, still-active debate over exactly how NMN gets into cells at all: one line of research points to a dedicated intestinal transporter (SLC12A8) that moves intact NMN directly, while other work suggests NMN is broken down to NR and rebuilt again once inside the cell. Both mechanisms may turn out to matter. The honest state of the science is that this part isn't fully settled.
CD38 — Real, But Only Half the Picture in Humans
Even NAD+ that makes it into circulation has to survive an active predator: CD38, an enzyme that breaks down NAD+ and its precursors. CD38 activity rises substantially with age, largely because chronic low-grade inflammation recruits more CD38-expressing immune cells into tissue — so older cells are simultaneously making less NAD+ and losing more of what they do make.
This is a real, well-characterized mechanism, and it's why pairing a precursor with a CD38 inhibitor is a coherent strategy rather than supplement-stacking for its own sake. Apigenin and quercetin — both common dietary flavonoids — were identified as CD38 inhibitors in foundational Mayo Clinic research, and have since shown benefits in animal models spanning metabolic disease, kidney injury, and cognitive decline.
What Liposomal Delivery Actually Solves
Wrapping an active ingredient in a lipid bilayer is not a universal upgrade — whether it helps depends on what, specifically, is going wrong for that particular molecule. That's worth spelling out plainly, because it isn't the same story for every ingredient:
| Molecule Type | The Real Constraint | Does Encapsulation Help |
|---|---|---|
| Bulk minerals (e.g. magnesium) |
Needs a large elemental dose; a lipid shell leaves little room for payload | Limited — dose size becomes the bottleneck |
| Fat-soluble actives (e.g. omega-3) |
Already lipid-compatible; main risk is oxidation, not encapsulation capacity | Genuinely — mainly by protecting freshness |
| Small, fragile organics (e.g. NMN, NR) |
Vulnerable to enzymatic breakdown before reaching tissue, not a volume problem | Plausible, and now has early human support |
NMN's problem isn't fitting a large dose into a small package. It's that raw NMN meets liver enzymes before it gets anywhere — which is exactly the kind of problem physical protection can address.
That's borne out, at least preliminarily, in direct human testing. A double-blind, placebo-controlled trial gave men over 40 either liposomal NMN, standard NMN, or placebo for four weeks at matched doses, and found liposomal NMN raised blood NAD+ significantly more than the standard form. It's a small study — fifteen participants — and one trial isn't the end of the conversation. But it's a real, direct human comparison, which puts liposomal NMN in a meaningfully stronger evidentiary position than "wrap it in a liposome" claims usually occupy.
The Verdict
The individual pieces of this story hold up to different degrees. NAD+ decline with age is about as well established as anything in this field. CD38's role in accelerating that decline is solid mechanistic science, though its flavonoid inhibitors are still waiting on human trials of their own. Liposomal delivery's advantage for NMN specifically has real, if early, human data behind it — a different evidentiary position than blanket "liposomal is better" claims usually occupy.
What's still genuinely open is the biggest question: whether raising blood NAD+ through any of these routes reliably delivers the downstream benefits — sharper cognition, better metabolic health, meaningfully slower aging — that motivate people to try this in the first place. Researchers running the human trials say so themselves. That's not a reason to wait on the sidelines, but it is a reason to want a protocol built on the parts of the science that are actually settled, rather than the parts that just sound settled.