The Science of NAD+ Debt — and How to Pay It Back

By Chris, founder of VAION

Alex has already told you how to get your routine back after summer, and step two of her plan was blunt: repay your cellular NAD+ debt. Her job was to tell you what to do. Mine is to show you the ledger, what summer actually withdrew, why the account runs down faster than it refills and what “paying it back” means at the level of your cells.

Before any of that: I founded a company that sells NAD+. You should factor that in while reading, the way you’d factor in a wine merchant’s enthusiasm for the health benefits of Burgundy. My defence is that everything below are mechanisms you can check, the free interventions are ranked above anything we sell and the section about our products is clearly signposted so you can skip it entirely.

The two jobs of NAD+

NAD+, nicotinamide adenine dinucleotide, and that’s the last time I’ll spell it out, is a molecule found in every living cell you own, doing two very different jobs. Nearly every confused claim you’ve read about it comes from mixing these jobs up, so hold onto this distinction; it’s the key to everything that follows.

Job one: the delivery van. When your cells burn food for energy, NAD+ collects electrons from the breakdown of glucose and fat and delivers them to your mitochondria, the structures that convert them into usable energy. The van isn’t consumed doing this. Empty van (NAD+) becomes loaded van (NADH), drops the cargo, becomes an empty van again. Round and round, all day.

Job two: the currency. A separate group of enzymes doesn’t borrow NAD+, they spend it, breaking the molecule apart to fund their work. The big spenders: PARPs, your DNA repair crews, which consume NAD+ every time they fix damage; sirtuins, regulators of metabolism and inflammation; and CD38, an enzyme on immune cells that degrades NAD+ in bulk and gets busier the more inflamed you are.

So your NAD+ level at any moment is a budget: income from your body’s recycling plant (an enzyme called NAMPT runs the production line, remember the name, it comes back later), spending by the repair and regulation enzymes and a fleet of vans that only work when they’re in the empty, NAD+ form.

Now let’s itemise the summer.

Withdrawal one: alcohol freezes the account

The popular version, “drinking destroys your NAD+”, isn’t quite right, and the accurate version is more interesting.

Metabolising alcohol requires NAD+ at two consecutive steps: one enzyme converts ethanol to acetaldehyde (the toxic intermediate responsible for much of how you feel the next day), and a second converts acetaldehyde to harmless acetate. Both steps load an empty van, NAD+ becomes NADH, and after a big night, they do it faster than your mitochondria can unload the vans at the other end.

Your total pool isn’t destroyed. It’s tied up. For hours, a large share of your NAD sits in the loaded NADH form while everything else that needed an empty van, fat metabolism, repair work, the lot, queues. Less “burning your savings”, more “freezing your account on the exact evening the bills arrive”. Do it three nights in a week and the queue never fully clears.

Withdrawal two: the sun sends repair bills, at every depth it reaches

Here’s the part of the summer ledger most people underestimate, because they think of sun damage as something that happens to the surface.

Sunlight isn’t one thing, it’s a spectrum, and different wavelengths reach different depths of you. UVB, the wavelength that gives you sunburn, is mostly absorbed in the epidermis, the outermost layer, where it strikes DNA directly and welds neighbouring letters of your genetic code together (the lesion is called a pyrimidine dimer, a typo that must be cut out and rewritten). UVA is longer-wavelength, makes up around 95% of the UV reaching the ground, passes through window glass and penetrates deeper, down into the dermis, the living layer beneath, where it does its damage less by direct hit and more by generating reactive oxygen species: unstable molecules that chew at DNA, mitochondria and collagen. Longer wavelengths still, visible light and near-infrared, reach deeper again, into the lowest skin layers and the tissue beneath, and have been shown to generate the same kind of oxidative stress.

Why does this belong in an NAD+ article? Because essentially all of that damage, at every depth, is repaired through processes with the same first responder: PARP enzymes detect the broken DNA and consume NAD+ to coordinate the fix. This isn’t theoretical. In studies of human skin cells, UV exposure measurably drains cellular NAD+ through PARP activation, and cells’ ability to withstand UV tracks with their capacity to rebuild NAD+ afterwards.

Honesty about the boundary of the evidence: the measured NAD+ depletion is demonstrated in skin, which is where sunlight deposits nearly all its energy. This is a bill paid locally by the largest organ you have, layer by layer, not a claim that a beach day drains your liver. But your skin is roughly a tenth of your body weight and its repair economy is not a rounding error. A week of sun is a week of accumulated repair invoices, every one of them payable in NAD+.

Withdrawal three: late nights sabotage the production line

This one doesn’t raid the account, it disrupts the income.

NAMPT, the rate-limiting enzyme of your NAD+ recycling plant, is under direct control of your circadian clock. The same molecular machinery that governs your sleep-wake cycle (a pair of proteins called CLOCK and BMAL1, for the enthusiasts) switches NAD+ production up and down on a daily schedule, and NAD+ levels genuinely oscillate through the day because of it.

Which means erratic sleep doesn’t just make you feel rough, it has your NAD+ factory running to a rota that no longer matches demand. Late nights, lie-ins, a 3am airport transfer: each one is less a withdrawal than a strike on the production line. This is also why the single best thing in Alex’s post, fixing your wake time before anything else, is mechanistically the right call, not just behavioural science.

Withdrawal four (minor, but real): six weeks of eating out

I’ll flag the evidence level clearly: this one comes mostly from animal studies, where sustained high-fat, high-sugar diets suppress NAMPT and lower NAD+ levels. Human data are thinner. I include it because the direction of the mechanism is consistent and because it compounds the others. A holiday diet doesn’t drain the account so much as quietly reduce the income while the withdrawals above are happening. A contributor, not a headline.

The two rules of repayment

So summer leaves you in NAD+ debt: spending up, production disrupted. Here’s what the biology says about paying it back, and it comes down to two rules.

Rule one: the tank defends a set point, so refilling obeys diminishing returns. Your cells actively hold NAD+ near a target level. Supply more raw material than the system wants and it doesn’t overfill: the surplus is tagged by an enzyme called NNMT and excreted in urine. Human trials show exactly this. Push the dose of an NAD+ precursor high enough and the methylated leftovers rise in step, while in one dosing study 600mg a day raised blood NAD+ just as much as 900mg. You cannot force the tank past full. The industry’s megadose end, the four-figure IV drip included, is, past a point, a very expensive way to manufacture unusual urine.

The useful flip side: repayment is most effective, and in my experience most noticeable, when you’re genuinely depleted. I’ll be precise about what’s evidence and what isn’t. The measured finding is the ceiling: top-ups do progressively less as you approach the set point. The personal observation is mine and it’s an n of 1. I feel far more from NAD+ supplementation in the week after excess than after a well-behaved month, which is exactly what the set-point logic would predict, because refilling a drained tank changes something while topping up a full one shouldn’t feel like much, most of it never getting used. Take that for what it is: a founder’s anecdote that happens to agree with the mechanism, not a trial result.

Rule two: ageing hits the budget twice. First, the pool itself shrinks: NAMPT production declines with age while CD38, that bulk NAD+ degrader on immune cells, rises with the low-grade inflammation that creeps up over the decades. Reported tissue declines range from roughly 10% to 50%, varying by tissue, and I’ll note honestly that human measurements are patchier than the marketing graphs imply. Second, and separately: your mitochondria become less efficient at unloading the vans. The electron transport chain, the machinery that re-oxidises NADH back into usable NAD+, slows with age, so more of whatever pool you do have sits stuck in the loaded form. A smaller fleet, and more of it parked. This is why the same August costs a 45-year-old more than a 25-year-old, and takes longer to repay.

NAD+ debt is sleep debt, almost

The best way to hold all of this is an analogy you already understand. NAD+ debt works like sleep debt: going into deficit occasionally is completely normal and completely recoverable; the drains are behavioural and they stack; and repayment starts with stopping the withdrawals, not just adding deposits. And the analogy holds at the other end too, which is rare for an analogy: just as you can’t bank ten hours of sleep and become superhuman, you can’t stockpile NAD+ past the set point.

Where it differs: sleep debt announces itself. You yawn, you fade, you fall asleep in meetings. NAD+ has no yawn. Blood NAD+ can be measured in a lab, but there’s no cheap consumer gauge, so mostly you’re navigating by the withdrawals you know you made rather than a fuel light. That’s an honest limitation of the whole field, mine included. What many people do report, and I’m one of them, is feeling the refill after a depleted stretch, even though they never felt the level itself.

So, the repayment plan, ranked by evidence rather than by price. A fixed wake time and morning light, because production runs on the clock: free. A pause on the withdrawals themselves, alcohol above all: free. Exercise, one of the few demonstrated ways to raise NAMPT and lift the income side: free. And then, if you choose, supplementation.

The part where I talk about my own products

Clearly signposted, as promised. Everything above stands whether or not you read on.

VAION exists because of one design conclusion from this same research: NAD+ turns over continuously, and the tank defends a set point, so if you supplement, steady daily delivery makes more physiological sense to me than an occasional megadose flood. That’s why we built daily micro-dose NAD+ Injection Pens (from £395, or £300/month on subscription) and an NAD+ Nasal Spray (from £199, or £150/month) for people who’d rather skip needles, both designed to bypass the gut, where oral NAD+ is heavily broken down, and to supply small amounts on the same continuous schedule your cells actually spend it.

The reason you should choose VAION for your NAD+ is that we use ZERO solvents or stabilizers – we don’t have to. We put a lot of time and resources into working out how to get NAD+ to dissolve in water through process and conditions and we are immensely proud of the purity, quality and stability of the end result. This is your body – you only get one – so we think what you put into it really matters. Quality (and thus your safety) matters above everything else.

— Chris, founder of VAION

This article is for information, not medical advice. Speak to a healthcare professional before starting any supplement, especially if you have a medical condition or take medication. Prices checked August 2026.