NAD+ is the cell's energy currency
Nicotinamide adenine dinucleotide, written NAD+, is a coenzyme present in every living cell. It does two essential jobs. It carries electrons through the metabolic reactions that produce ATP, the molecule cells use for energy, and it activates the sirtuin and PARP enzymes that maintain DNA integrity.
When NAD+ is abundant, mitochondria run cleanly, DNA repair runs continuously, and cellular stress responses fire on time. When NAD+ falls, all three slow down.
The decline is measurable
NAD+ levels in human tissue drop by roughly 50 percent between age 20 and age 50. The decline accelerates after 60. Lower NAD+ correlates with reduced mitochondrial function, slower DNA repair, and the cellular signatures associated with aging.
This is not a hypothetical decline. It has been measured directly in skin, muscle, brain, and liver tissue across multiple human studies.
Why oral NAD+ does not work
NAD+ itself is too large and too charged to cross the cell membrane intact. Take NAD+ orally, and it gets broken down in the gut before it ever reaches systemic circulation. This is why intravenous NAD+ infusions exist as a clinical protocol, and why oral NAD+ supplements deliver close to nothing.
The body has its own solution. It is called the salvage pathway.
The salvage pathway
Cells continuously break down NAD+ and rebuild it from smaller precursors. The two precursors with strong human data are nicotinamide riboside, written NR, and nicotinamide mononucleotide, written NMN. Both are small enough to enter cells and are converted to NAD+ inside the mitochondria within hours of ingestion.
Human trials with NMN at 250 to 500 mg daily show measurable increases in blood NAD+ levels, improvements in walking endurance in older adults, and improved insulin sensitivity. The effect builds over weeks of consistent dosing, not from a single capsule.
How to dose it
Morning, with food. NAD+ activity follows a circadian rhythm and peaks during the daytime. Evening dosing can interfere with the natural drop in cellular metabolism that supports sleep.
Stack with methylated B-complex if you can. The salvage pathway uses methyl groups as cofactors, and methylation status is the rate-limiting step in NAD+ regeneration for many adults.
What to expect
NAD+ is foundational, not symptomatic. You will not feel a single dose the way you feel caffeine. What you will notice over four to eight weeks is steadier daytime energy, faster recovery from physical effort, and a clearer cognitive baseline. The deeper effects, on DNA repair and sirtuin activity, are not perceived directly. They run quietly in the background, doing the work the body used to do at 25.
