NAD+ Cycle: Duration, and Where It Comes From
One of these two cycles has been running inside you all day. The other was set by how many appointments fit in a package.
The phrase NAD+ cycle is doing two unrelated jobs at once, and almost every page that uses it lets the credibility of the first meaning leak into the second. One is a real biochemical loop, continuously running, well described for decades. The other is a block of appointments with a price attached. Separating them takes one paragraph and changes what the rest of the subject looks like.
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The real NAD+ cycle, which has been running all day
Start with the loop that actually exists, because it is the reason the commercial one makes so little sense.
The coenzyme is not stockpiled and gradually spent. It moves between two forms continuously as it carries electrons through metabolism, oxidised and reduced and oxidised again, thousands of times over. That is one cycle, and it is fast.
There is a second and slower loop underneath it. A group of enzymes, the sirtuins, the PARP enzymes and CD38, do not simply borrow the molecule. They cleave it, using it up and leaving nicotinamide behind. Cells then rebuild it from that nicotinamide through what is called the salvage pathway, reassembling the coenzyme from the wreckage of the last one. Consumption and resynthesis run against each other constantly, and the concentration you have at any moment is the balance between them rather than a tank level.
That word salvage is the useful one. The body is not waiting for a delivery. It is recycling continuously, and it has been doing so without interruption since before you read this sentence.
Why a continuously rebuilt pool changes what a course could mean
Now put an infusion against that picture and the question becomes concrete rather than rhetorical.
An appointment delivers a quantity over a couple of hours, on a small number of occasions, into a system that manufactures and destroys the molecule continuously and holds the balance where its own regulation puts it. For a course of sessions to produce a lasting change, the delivered quantity would have to shift that balance and the shift would have to persist after delivery stopped. Neither has been demonstrated for the injected form.
This is not an argument that nothing happens during an infusion. Something clearly happens, since people feel it. It is an argument about what a schedule could plausibly be a schedule for. A regulated, self replenishing pool is a poor match for the idea of a loading period followed by maintenance, which is a shape borrowed from drugs that accumulate and then wash out.
The commercial cycle, and the unit it was actually built from
Follow a stated course length backwards and it arrives somewhere unglamorous.
Infusion services are sold as blocks: a run of sessions close together, then spaced sessions afterwards. Ask what fixes the number in the block and there is no published answer, because there is no trial that compared one arrangement against another and reported which did better. What there is, is a price. A block of sessions is a unit that can be quoted, discounted and paid for in advance, and it fills a clinic's diary in a predictable way.
Once the block exists, language accretes around it. The first run becomes loading. The gap becomes maintenance. Neither term was earned by a measurement, and both are borrowed from pharmacology where they mean something specific about a drug reaching a steady concentration in blood.
The same applies to vendor schedules for the home injected form, with one difference. There the number tends to track how much powder is in a vial, which is a manufacturing and shipping decision, not a biological one.
What the precursor trials fixed instead of a course
There is one place in this subject where a treatment period was chosen deliberately, and it is worth naming precisely because it does not transfer.
In a registered trial of an oral precursor, the treatment period exists to serve a measurement. Researchers decide what they will read and when they will read it, and the period is whatever fills the gap between starting the intervention and taking that reading. It is fixed before the first participant enrols, it applies to a defined population, and it ends at a scheduled assessment rather than when a container empties.
Those periods, typically weeks to months of daily oral nicotinamide riboside or nicotinamide mononucleotide in human participants, are real durations with real justifications. They justify a measurement, not a course of treatment, and they were set for capsules rather than for a drip. Reading a trial's treatment period as a recommended course length inverts what the number was for.
Where the two meanings get welded together
The conflation is rarely done openly, and it does not need to be.
A page opens with the biochemistry, correctly, describing a coenzyme that is consumed and regenerated in a continuous loop. A few paragraphs later it introduces a schedule of sessions. Nothing in between claims that the second follows from the first, and nothing has to. The word cycle has already appeared in a paragraph the reader accepted, so when it reappears attached to a purchase it arrives pre approved.
That is a rhetorical move rather than an argument, and it is worth naming because it is the load bearing part of most copy on this subject. The genuine cycle is a fact about metabolism that would be true if no clinic existed. The commercial one is a fact about how services are sold. Sharing a noun does not make the second a consequence of the first.
| Candidate source of a duration | What it would fix | Status for injected NAD+ |
|---|---|---|
| Approved labelling | A course for a defined indication, with warnings | Does not exist, no authorisation anywhere |
| A completed trial of the injected form | A period fixed before enrolment and reported | No such published trial |
| Oral precursor trial periods | A window chosen to serve a blood measurement | Real, for capsules, in humans, does not transfer |
| Rodent work | Experimental periods anchored to a scheduled reading | Not convertible to a person |
| A clinic package | How many sessions are being sold together | This is where the circulating blocks come from |
| Vial size | How much powder a supplier chose to fill | This is where home schedules come from |
The measurement that would have to close a course, and does not exist
Every real treatment period ends at a decision, and the decision is the part that never survives into a consumer version.
A trial's period ends at a scheduled assessment, read by someone who does not know which group the participant was in, against a baseline recorded in advance. A course of medical treatment ends at a review by a clinician who examined the patient. In both cases the duration is downstream of a stopping rule.
A block of infusions has a stopping rule too, and it is that the block is finished. Whatever the person concludes at that point is an impression formed on an ordinary day, without a baseline, without a comparison and knowing exactly what they received. There is no reading, so there is nothing the course could have failed at, and a course that cannot fail cannot be corrected. It can only be repeated, which is what the maintenance schedule is for.