Few molecules in longevity medicine have drawn as much attention as nicotinamide adenine dinucleotide, better known as NAD+. It is worth understanding what the research actually supports, because the marketing has run well ahead of the evidence.
What NAD+ does
NAD+ is a coenzyme your cells cannot function without. It is essential to oxidative phosphorylation, the process mitochondria use to turn nutrients into ATP, and it acts as a substrate for several enzyme families tied to aging biology.
Those include the sirtuins, which regulate cellular stress resistance and metabolic efficiency, the PARP enzymes responsible for DNA repair, and CD38, which governs immune signaling and inflammation. When NAD+ runs low, all of that work gets harder.
It declines with age, for several reasons at once
Tissue NAD+ levels fall measurably across the lifespan. Work published in Cell in 2013 by Gomes and colleagues showed that declining NAD+ disrupts communication between the nucleus and the mitochondria, producing a pseudohypoxic state that impairs mitochondrial function during aging.
Three things drive the decline. Consumption rises, as enzymes like CD38 become more active with age. DNA damage accumulates, and PARP enzymes burn through NAD+ repairing it. And synthesis slows, because the enzymes that build NAD+ lose activity. The net effect is less mitochondrial efficiency, less repair capacity, and less metabolic flexibility.
Why the brain comes up so often
Neurons are unusually dependent on mitochondrial energy, which makes them sensitive to falling NAD+. Eric Verdin's 2015 review in Science laid out the case that declining NAD+ during aging contributes to mitochondrial dysfunction, metabolic disease, and neurodegeneration, and that restoring it in preclinical models improves mitochondrial function and extends lifespan.
Preclinical work has since suggested that raising NAD+ protects against axonal degeneration and supports neuronal survival. That is genuinely promising. It is also not the same as showing that a supplement prevents dementia in humans, and anyone who tells you otherwise is ahead of the data.
The metabolic side
Mitochondrial dysfunction sits underneath insulin resistance, metabolic syndrome, cardiovascular disease, chronic fatigue, and the age related drop in aerobic capacity. Animal studies show that NAD+ repletion improves mitochondrial function and glucose tolerance, which is why it keeps appearing in metabolic optimization programs.
What raising it actually involves
Nicotinamide riboside is the precursor with the clearest human bioavailability data, and randomized trials have shown it raises NAD metabolites in human tissue. Nicotinamide mononucleotide is widely sold, but its regulatory status as a supplement in the United States is unsettled, which is worth knowing before you buy it.
Lifestyle does real work here too. Zone 2 aerobic training, time restricted eating, sauna exposure, and properly aligned sleep all support NAD dependent signaling through pathways like AMPK and the sirtuins. None of that is exotic, and all of it is free.
Where it fits in a plan, and when
Longevity programs here run in four phases, and NAD work belongs in the last one.
First, define the objective. Cardiometabolic health, body composition, cognitive performance, disease risk, or healthspan generally. You cannot build a plan without knowing what you are moving toward.
Second, assess the systems. Laboratory analysis and physiologic testing across metabolic health, inflammation, hormones, micronutrients, and cardiometabolic risk, which is where the actual imbalances surface.
Third, fix the foundations. Nutrition, exercise prescription, sleep, and the nutraceutical or prescription protocols that stabilize your core physiology.
Fourth, and only then, add advanced interventions. NAD repletion sits here, alongside other approaches aimed at mitochondrial function and cellular repair. Adding it earlier is a common and expensive mistake, because it will not compensate for poor sleep, untreated insulin resistance, or a hormone problem nobody has looked at.
