NAD+ for endurance capacity: reading the trials past the marketing

There is a walking-distance study buried in the NAD+ literature that gets cited constantly in supplement marketing and almost never described accurately. Short answer: NAD+ precursors have real human trial support for functional endurance-adjacent outcomes in people with vascular or metabolic impairment, but the jump to "NAD+ boosts endurance capacity" for a healthy trained person is mostly inference, not direct evidence.

I get asked about this a lot, usually by someone who read that NAD+ improves mitochondrial energy production and assumed that meant faster 5Ks or a bigger deadlift set. I understand the instinct. NAD+ genuinely is the molecule your mitochondria use to shuttle electrons and generate ATP, and it does decline with age. But "mitochondria need it" and "more of it makes you fitter" are two different claims, and the second one needs its own evidence.

What the trials actually measured

The best functional data point in the NAD+ literature for anything endurance-adjacent is a 2024 trial that gave nicotinamide riboside to people with peripheral artery disease, a condition where narrowed leg arteries cause pain and limited walking distance during exertion. Over the trial period, NR improved six-minute walk distance by 17.6 meters compared to placebo. That is a real, measured functional gain in people whose exercise capacity was limited by a vascular and metabolic problem NAD+ repletion plausibly addresses.

That is not the same population as a 32-year-old runner trying to shave time off a half marathon. In PAD, the tissue is oxygen-starved and NAD+-dependent repair and energy pathways are under real strain. In a healthy trained athlete, mitochondrial density and NAD+ recycling capacity are already high from training itself. Whether topping off NAD+ moves the needle further in that population is a much harder question, and it is one the trial base has not directly answered.

The biochemical foundation is solid regardless. NR reliably raises blood NAD+ in a dose-dependent way: a 2019 dose-response trial found increases of 22%, 51%, and 142% at 100, 300, and 1000 mg respectively. That result is one of the most reproducible findings in the whole NAD+ literature. What is not settled is whether raising the blood marker translates into a performance gain you would feel on a bike or a track. In a group of already-healthy older men, NR raised the muscle NAD+ metabolome without changing measured bioenergetics, which is a fairly direct data point against assuming the biochemical bump always becomes a functional one.

Where the real endurance lever already lives

Here is the part that gets buried under the supplement pitch. Exercise itself increases NAMPT, the enzyme that is the rate-limiting step in how your body recycles NAD+ in the first place. A 2010 human training study found skeletal muscle NAMPT protein rose roughly 127% after just three weeks of training in previously sedentary people. That is the free lever sitting underneath the whole conversation, and it works whether or not you ever touch a precursor supplement. If you're chasing endurance capacity, the training stimulus itself is doing the NAD+ recycling job that the supplement is trying to support from a different angle.

That does not mean precursor supplementation is pointless for an endurance athlete. It means the honest framing is: NAD+ precursors support the metabolic substrate your training-adapted machinery runs on, and exercise builds the machinery. Neither one substitutes for the other, and a supplement is not going to manufacture the adaptation that consistent training produces.

I see this pattern with clients constantly. Someone adds a longevity stack expecting it to move a performance number that is actually gated by training volume, sleep, and recovery. The stack might genuinely help the underlying cellular economy, but it is not going to close a training gap.

For a deeper look at what NAD+ is doing mechanistically and how the oral, subcutaneous, and IV routes compare, the full NAD+ profile covers the CD38 and PARP drain mechanisms, the dosing protocols people actually use, and the contraindications worth knowing before you start. If fatigue rather than pure endurance output is your actual complaint, it's also worth reading what the data shows on 5-Amino-1MQ for fatigue and energy, since the two compounds address different ends of the same cellular-energy problem.

Dosing, if you want to test it yourself

If you want to run this as a self-experiment, the studies used oral NR in the 100 to 1000 mg range, with the 300 to 1000 mg range being where the dose-response data is strongest. In practice, most people running NR for a general energy or mitochondrial-support goal land on 300 to 1000 mg per day, taken with food in the morning to avoid any sleep disruption. For NMN, the trial showing a clear functional benefit (improved muscle insulin sensitivity in prediabetic women) used 250 mg per day, and that is the range most people run, staying well clear of the roughly 2 gram per day territory where a reduced-muscle-mass signal has shown up.

Now the part my lawyer makes me say, and he is right: the doses and schedules here are for educational and informational purposes only. These peptides are sold for research use only and are not FDA-approved drugs. This is not medical advice. Consult a qualified physician before beginning any protocol.

What I'd actually tell you

If your goal is endurance capacity and you are already training consistently, the evidence supports NR as a well-tolerated way to reliably raise NAD+, and it may be worth running alongside your training rather than instead of it. If you are dealing with vascular limitation, reduced walking tolerance, or a diagnosed metabolic issue, the trial data is considerably stronger and more directly relevant to you. What the evidence does not support is treating NAD+ as a shortcut around the training adaptation itself. The exercise-driven NAMPT increase and the supplement-driven precursor supply are doing complementary jobs, not competing ones, and neither one replaces the other.

I try to stay evidence-based with peptides and their adjacent compounds, and this is one of those cases where the honest picture is more interesting than the marketing version. The molecule is real, the mechanism is real, and the walking-distance data in a clinical population is real. The leap to "faster mile times for healthy people" just is not where the current trial base sits yet.