Nicotinamide adenine dinucleotide, or NAD+, is a coenzyme present in every living cell. It plays two distinct roles that matter for energy and aging: it's a required cofactor in the electron transport chain (the same ATP-production process CoQ10 participates in), and it's a substrate that sirtuins — a family of proteins linked to cellular repair and stress resistance — consume in order to function.
The decline is well-documented
Multiple studies measuring NAD+ levels across age groups have found a substantial decline from young adulthood to older age — commonly cited estimates put it at roughly a 50% reduction by middle age compared to youth. The proposed consequences include reduced mitochondrial efficiency and reduced sirtuin activity, both of which are active areas of aging research.
Why you can't just take NAD+
NAD+ itself is a large, charged molecule that doesn't cross cell membranes efficiently when taken orally — it's largely broken down in digestion before it could raise cellular NAD+ levels directly. This is why supplements target precursors instead: smaller molecules like NMN (nicotinamide mononucleotide) or NR (nicotinamide riboside), which cells can actually take up and convert into NAD+ internally through well-characterized enzymatic pathways.
This distinction — precursor versus the molecule itself — is a good example of why we publish the mechanism alongside the dose. "Contains NAD+" and "contains an NAD+ precursor" are very different claims, and the difference is the whole reason one of them works when taken as a pill and the other largely doesn't.
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