In the last post I made the case that low NAD+ in ageing tissue isn't really a supply problem — it's a consumption and diversion problem. Pour more precursor into a system that's actively draining and wasting NAD+, and you've chosen the least efficient fix available.

That post named the problem. This one is about the machinery: how the pathway actually works, and what the research says about targeting each part of it. Because once you see it as real enzymes doing real things — not as an analogy — your whole approach to NAD+ changes.

Here's the strange part. The scientists who study NAD+ metabolism for a living have described all of this clearly for years. The supplement market quotes their work when it's convenient and quietly skips the inconvenient half. Let me give you the half that usually gets left out.

The map: three forces, not one shortage

Quick recap, because everything below hangs off it.

Three forces drive age-related NAD+ decline, and none of them is "you're not taking enough precursor." CD38 is the drain — the enzyme that breaks NAD+ down, thrown wide open by the inflammation of ageing. NAMPT is the recycler — the rate-limiting step in the loop that regenerates NAD+, and it slows with age. NNMT is the side-pipe — it siphons your raw material away before it ever becomes NAD+, and spends your methyl reserves doing it.

A serious strategy works on all three, plus the precursor, plus what NAD+ is actually for. Let me take them in turn.

CD38: plug the drain before you touch the tap

If there's one villain in the NAD+ ageing story, it's CD38.

CD38 is the dominant NADase in human tissue — the main enzyme that consumes NAD+ and breaks it down. The work that nailed this came out of Eduardo Chini's lab at the Mayo Clinic. They showed that CD38 expression and activity climb steadily with age, and that this rise isn't just correlated with the NAD+ drop — it's largely causing it. In their animal models, CD38 was required for age-related NAD+ decline. Remove the enzyme, and the animals held onto their NAD+ and were protected from the metabolic dysfunction that normally arrives with age.

Why does CD38 climb? This is the part that ties everything together. CD38 sits heavily on immune and inflammatory cells, and its expression is driven up by the chronic, low-grade inflammation of ageing — inflammageing. It gets worse. Senescent cells, the zombie cells that accumulate with age and refuse to die, secrete an inflammatory cocktail known as the SASP, and that cocktail directly induces CD38 in neighbouring healthy cells, ramping up NAD+ breakdown.

Sit with that, because it reframes the whole category. The same inflammatory ageing process you're trying to push back is the thing holding the drain wide open. You can pour precursor in all day, but if CD38 is upregulated and running hot, you feed the enzyme as fast as you feed the cell. Worse still, CD38 is one of the main enzymes that degrades NMN itself — so the precursor most people reach for can be consumed before it's even converted.

This is the single biggest reason a single-precursor product underdelivers. It does nothing about the drain.

So what targets CD38? You don't need a pharmaceutical inhibitor in your cupboard. Chini's group — in work co-authored by David Sinclair — characterised natural compounds that do the job: the flavonoids apigenin and quercetin were shown to inhibit CD38 in vitro, raise intracellular NAD+, and, in apigenin's case, improve metabolic markers in obese animals through exactly this mechanism.

Now the honest caveat, because credibility is the entire point. That evidence is largely in-vitro and animal. The human translation of CD38 inhibition is still emerging, and I'm not going to pretend otherwise. But the mechanism driving the decline is well established — which is enough to know that ignoring CD38 is a mistake, and that the smartest first move is upstream: calm the inflammation and senescence that drive the enzyme in the first place. Plug the drain before you worry about the tap.

NAMPT: repair the recycler, don't just add fuel

Now the plumbing.

Most of the NAD+ in your cells isn't made fresh from scratch. It's recycled, thousands of times a day, through the salvage pathway: niacinamide to NMN, NMN to NAD+, NAD+ used and broken back down to niacinamide, round and round. The enzyme that sets the speed of that loop is NAMPT, and it's the rate-limiting step. Whatever NAMPT can process is the ceiling on salvage throughput, no matter how much raw material you supply. Jun Yoshino's work at Washington University did much to establish how central NAMPT is to NAD+ biosynthesis and metabolic health.

The problem with age: NAMPT activity declines. The recycling plant slows at exactly the stage of life you most need it humming.

This is where precursor-only fails a second time. Picture a motorway with a single-lane bottleneck. Adding more cars doesn't increase throughput when every car still funnels through the one lane — you get a longer queue, not more flow. More NMN or NR behind a flagging NAMPT is exactly that: more input, same throughput, substrate piling up behind the bottleneck.

The intelligent move is to widen the lane. Rutin belongs to a family of flavonoids associated with supporting the cellular pathways involved in NAD+ recycling, including mechanisms linked to NAMPT itself. I'll be straight with you: the research here is still evolving, and I'd rather say so than overstate it. But the intent is the point — not handing the cell more raw material, but supporting the machinery that recycles what's already there. One philosophy says "here's more fuel." The other says "let's repair the engine." Only one of those helps a cell whose recycling capacity is already fading.

NNMT: close the side-pipe, and protect your methyl pool

The third force is the one almost nobody mentions, and it's the one I find most interesting — because it explains a real problem with high-dose NMN that rarely gets discussed honestly.

NNMT — nicotinamide N-methyltransferase — takes niacinamide and methylates it into methyl-nicotinamide, which then gets cleared from the cell. In isolation, that's normal disposal. But when you're trying to build NAD+, NNMT does two unhelpful things at once.

First, it diverts niacinamide away from NAD+ synthesis. Every molecule NNMT grabs is one that never enters the salvage pathway — the side-pipe siphoning water out before it reaches the tub.

Second, and this matters enormously for a lot of people, it burns a methyl group to do it, consuming SAMe, your body's primary methyl donor. That's the same currency you rely on for detoxification, neurotransmitter balance, hormone clearance and DNA methylation. Run NNMT hard and you are spending down your methylation pool.

Connect that to the real world. If you carry an MTHFR polymorphism, or you're already under methylation stress — and a great many people are — this compounds. You're trying to support NAD+ and taxing an already-stretched methylation system in the process.

This is also the honest answer to a question I'm asked constantly: what about the methylation burden of high-dose NMN? It's fair. High precursor exposure can increase the substrate available for NNMT-mediated methylation, and with it the methylation cost. The smart response isn't to wave the concern away — it's to inhibit the enzyme doing the damage. EGCG, the active catechin in green tea, is reported to inhibit NNMT, which does two good things at once: it preserves niacinamide for actual NAD+ synthesis, and it protects your methylation pool from being needlessly drained. For anyone methylation-sensitive, that second effect may be every bit as valuable as the NAD+ benefit itself.

The precursor question: fit beats raw strength

Once you understand those three forces, choosing a precursor stops being a marketing decision and becomes a biochemical one.

Let me be clear about what I'm not saying. Niacinamide is not the strongest standalone NAD+ precursor. On their own, NR and NMN raise blood NAD+ very effectively, and in simple biomarker studies they often outperform niacinamide. The point is different: niacinamide may be particularly effective precisely when it's paired with strategies that reduce degradation, support recycling and preserve utilisation. In a pathway-optimised context, it fits in a way the others don't.

It enters the salvage pathway directly through NAMPT — the very enzyme you've just worked to support. So the precursor and the pathway-support pull in the same direction rather than against each other. Worth noting here: NMN bypasses NAMPT, so it can't benefit from NAMPT support the way niacinamide can.

It sidesteps the methylation burden that worries people about high-dose NMN, particularly when NNMT is being held in check at the same time. And it avoids the flush — anyone who's taken niacin knows that hot, prickly, red-faced experience. Niacinamide doesn't do that.

There are also two findings that set niacinamide apart, and they deserve honest weight and honest caveats in equal measure.

The first is muscle. A study from the Nestlé research group found that niacinamide, paired with vitamin B6, expanded muscle stem cells and improved regeneration in ageing. The interesting part is the mechanism. Niacinamide drove the stem cells to proliferate through a route that had nothing to do with NAD+ — a separate signalling pathway involving beta-catenin, holding up even when NAD+ synthesis was blocked, with vitamin B6 pushing differentiation alongside it. That's a nicotinamide-specific action, not something an NAD+ precursor like NR would trigger. If it replicates, it's a genuinely distinctive benefit for anyone serious about preserving muscle with age, which at my end of the longevity conversation is everyone. I'd file it as promising rather than settled.

The second is the gut. Research tracing where oral NR actually goes has shown something the marketing rarely mentions: a large fraction isn't absorbed and used intact. Gut bacteria break it down and convert it, via a deamidation route, before it can meaningfully raise NAD+ in tissues like the liver. Deplete the microbiome with antibiotics and NR's ability to lift host NAD+ is substantially blunted. The emerging picture is that the gut microbiome plays a real role in how efficiently NR is metabolised and put to use.

Now think about who actually buys NAD+ supplements. Often older people, frequently with the dysbiotic, depleted gut that comes with age, medications and decades of modern living. If a precursor's efficiency is tied to a well-populated microbiome, and your microbiome is exactly the thing age has worn down, that's worth factoring in. Niacinamide doesn't carry the same reliance.

The payoff: NAD+ is the means, not the end

Restoring NAD+ isn't the goal in itself. What NAD+ lets your cells do is.

This is where resveratrol earns its place. Trans-resveratrol has been shown to influence SIRT1 signalling — the pathways tied to mitochondrial function and cellular resilience. With NAD+ available as the fuel, SIRT1 drives PGC-1-alpha, the master regulator of mitochondrial biogenesis. That's the prize at the end of the chain: not a number on a NAD+ assay, but more and healthier mitochondria, which is what actually translates into energy, resilience and the cellular vitality we're all chasing.

So put it all together. Plug the drain by inhibiting CD38, the enzyme inflammageing and senescent cells have thrown into overdrive, and ideally calm that upstream inflammation too. Widen the bottleneck by supporting NAMPT, the rate-limiting recycler that fades with age. Close the side-pipe by inhibiting NNMT, protecting both your niacinamide and your methyl pool. Choose a precursor that feeds the pathway you've just optimised, dodges the flush and the methylation cost, and doesn't depend on a gut you can't guarantee. Then convert restored NAD+ into the mitochondrial outcome you're actually after.

That's a multi-pathway, cofactor-led approach — not because multi-pathway sounds impressive on a label, but because that's what the biology demands. The people studying NAD+ at the highest level have been describing this picture for years. The job is simply to listen to it.

One free thing: take it in the morning

A practical note, because it costs nothing and it matters.

NAD+ is a circadian molecule — its levels rise and fall on a daily rhythm tied to your body clock. A study in Nature Communications showed that when you raise NAD+ matters as much as whether you do. In the animal model, increasing NAD+ before the active phase improved body weight, glucose control, insulin sensitivity and liver inflammation. Raising it before the rest phase didn't just fail to help — it compromised those same responses and pushed the liver clock out of alignment. Same compound, opposite outcomes, purely on timing. Human data is still limited, so I hold the specifics lightly, but the principle is biologically sound and the cost of acting on it is zero.

For a daytime species like us, the translation is simple: take your NAD+ support in the morning, at the start of your active day. Working with your circadian biology instead of against it is one of those small, free decisions that quietly compounds.

That's the whole picture. Fill the tub, yes, but first plug the drain, repair the plumbing, and close the side-pipe. Anything less is just an expensive way to water the floor.

I'm building a formulation around exactly this logic: a cofactor-led, multi-pathway approach that works on the whole system instead of flooding it with one more precursor. It's not ready for a name yet, but it's close. The early-access list gets first sight of it, with founding-member pricing held back for that group alone. If the thinking in this post lands for you, that's the list you want to be on. Add your name here: https://shop.lisatamati.com/pages/nad-next-gen-waitlist