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Preiss-Handler —
the third road
to NAD+.
The body does not build NAD+ in only one way. Two routes have been described in this library — the de novo pathway, which assembles it from scratch, and the salvage pathway, which recycles it. There is a third, named for the two researchers who first traced it: the Preiss-Handler pathway, the road that begins with niacin. Here is how that route runs, and where it sits among the three.
I
A third way
to the same molecule.
NAD+ is not made by a single process. The cell has more than one route to it, each starting from a different material and arriving at the same destination. This library has followed two of them: the de novo pathway, which builds NAD+ from the amino acid tryptophan, set out in Building NAD+ From Scratch; and the salvage pathway, which recycles nicotinamide back into NAD+ rather than discarding it. Between and alongside these sits a third route, less often named but no less real.
That third route is the Preiss-Handler pathway, named for Jack Preiss and Philip Handler, the researchers who first traced its steps. It begins not with tryptophan and not with nicotinamide, but with niacin — specifically nicotinic acid, one of the two forms of vitamin B3. From there, a short, defined sequence of steps converts it into NAD+. It is the road that runs from a dietary vitamin to the finished coenzyme this series has just described.
Naming it matters because it completes the account of how NAD+ comes to be. A molecule the body relies on is not arrived at by one road only; it is reached by several, each suited to the material at hand. The Preiss-Handler pathway is the one that takes a form of vitamin B3 and carries it through to NAD+ — the third of the routes, and the one most directly tied to a vitamin on the plate.
Three roads, one molecule.
From scratch, from recycling,
and from a vitamin —
the Preiss-Handler pathway
is the third way to NAD+.
The Route, in Brief
Where it starts,
and what it is.
A short profile of the Preiss-Handler pathway — its starting material, its shape, and its place among the routes. All descriptions here are drawn from independent research that did not involve any specific Codeage product.
The pathway starts from nicotinic acid, one of the two forms of vitamin B3 commonly grouped under the name niacin. This is its distinguishing feature: where the salvage route begins with nicotinamide and the de novo route with an amino acid, Preiss-Handler begins with nicotinic acid specifically.
From nicotinic acid, the pathway proceeds through a small number of defined steps — each carried out by its own enzyme — converting the starting vitamin into NAD+. It is a compact route: a few transformations, in order, from entry to finished molecule.
Preiss-Handler is the third of the recognized routes to NAD+, alongside de novo synthesis and the salvage pathway. Together, the three give the cell more than one way to arrive at the same molecule, from more than one starting material.
II
Where the third road
fits.
The value of three routes is that they do not all depend on the same starting point. De novo synthesis draws on an amino acid; salvage draws on nicotinamide already in circulation; Preiss-Handler draws on nicotinic acid. Different inputs, the same output — NAD+ — reached by different chemistry. A system with more than one road to a molecule it relies on is a system less tied to any single source of it.
The three routes also connect to the precursors discussed elsewhere in this library. The forms grouped as vitamin B3 — nicotinic acid and nicotinamide — and precursors such as NMN and NR each enter the NAD+ story at a particular point; the NAD+ precursor family sets out where each one sits. The Preiss-Handler pathway is, in effect, the route that nicotinic acid takes once it enters.
None of this places one route above another. Each is a way the cell can reach NAD+, suited to the material it starts from; the body uses what is available. To name the Preiss-Handler pathway is simply to complete the map — to account for the third road, so the picture of how NAD+ is made is whole rather than partial.
Three Roads to NAD+
Different starts,
one destination.
The three recognized routes the body uses to reach NAD+, each beginning from a different material.
Route 01 · De Novo
From tryptophan
The route that builds NAD+ from scratch, starting with the amino acid tryptophan and assembling the molecule across many steps — the body's from-first-principles option.
Route 02 · Salvage
From nicotinamide
The recycling route, which takes nicotinamide released when NAD+ is used and returns it to NAD+ rather than discarding it — a recycling loop that reuses what the cell already has.
Route 03 · Preiss-Handler
From nicotinic acid
The third route, beginning with nicotinic acid — a form of vitamin B3 — and converting it to NAD+ through a short, defined sequence of steps.
The Routes in Brief
How NAD+ is
arrived at.
3
Recognized routes to NAD+ — de novo, salvage, Preiss-Handler
The cell can reach NAD+ from more than one starting material. Research describing these routes was conducted independently and did not involve any specific Codeage product.
1
Destination — every route arrives at NAD+
Different inputs, different chemistry, one shared endpoint: the same NAD+ molecule this library has read down to its parts.
1
Vitamin at the start of the Preiss-Handler route — niacin
The pathway begins with nicotinic acid, one of the forms of vitamin B3, and carries it through a short sequence of steps to NAD+.
III
The map,
completed.
With the Preiss-Handler pathway named, the routes to NAD+ are all accounted for. The body can build the molecule from scratch, recycle it from what it has already used, or convert it from a dietary form of vitamin B3 — three roads, arriving at one destination. Each was traced by researchers over decades; together they describe how a molecule found in every living cell is continually made and remade.
Keeping each route described as what it is — a defined sequence of chemistry — is the discipline this series has kept throughout. A pathway is a map of chemistry; naming the third road completes the map without ranking the roads on it. As always, the finer details of how these routes are used and balanced in the body continue to be studied, and the account here stays with what is established: that the third road exists, where it starts, and where it arrives.
To trace how NAD+ is made, by every route the body has, is one expression of Cellular Longevity — Pillar 03 of The Longevity Code, the dimension of the system built around NAD+ biology and the science of how cells sustain themselves across time. To know the Preiss-Handler pathway is to see the full set of roads that arrive at the molecule at its center.
From scratch, from recycling,
and from a vitamin.
Three roads, one molecule —
the Preiss-Handler pathway
completes the map to NAD+.
Codeage · Pillar 03 · Cellular Longevity
Built for the
cellular long game.
Cellular Longevity is Pillar 03 of The Longevity Code — the dimension of the system built around NAD+ biology, mitochondrial health, and the science of cellular aging.
Explore Cellular Longevity →Research and studies referenced throughout this article were conducted independently and did not involve any Codeage products. Statements have not been evaluated by the FDA. Codeage products are not intended to diagnose, treat, cure, or prevent any disease.
