There is a molecule present in every one of your cells, without exception. It participates in more than 500 biochemical reactions. It governs your energy production, DNA repair, biological-clock regulation, and the activation of cellular defence mechanisms against aging. Its name: NAD+, nicotinamide adenine dinucleotide.
At 20, your cells are overflowing with it. By 40, you've lost half of it. By 60, levels may have fallen by 80% compared to your youth.
This decline isn't trivial. In contemporary cell biology, it represents one of the best-documented mechanisms of human aging — and one of the most studied by geroscience researchers over the past decade.
What is NAD+, and why is it so central?
NAD+ is a coenzyme — an auxiliary molecule essential to the function of hundreds of enzymes in the body. It operates in two interconvertible forms — NAD+ (oxidised) and NADH (reduced) — and it is precisely this back-and-forth that enables the electron transfer at the heart of cellular energy production.
The sirtuins (SIRT1 through SIRT7) are NAD+-dependent deacetylases. They regulate gene expression, the cellular stress response, DNA repair and mitochondrial biogenesis. Without sufficient NAD+ available, sirtuins can't function — and their progressive inactivation is associated with accelerated epigenetic aging.
PARPs (Poly ADP-ribose polymerases) consume NAD+ massively to repair DNA breaks. With age, DNA damage accumulates, PARP demand rises, and NAD+ reserves deplete all the faster. CD38, an enzyme whose expression rises significantly with age and chronic inflammation, is one of the main consumers of NAD+ in the aging body.
The decline curve: data that doesn't lie
One of the most cited studies on this topic, published in Cell Metabolism in 2012 by Johan Auwerx's team at EPFL, showed that NAD+ levels in mouse skeletal muscle fall dramatically with age — and that this drop precedes and predicts mitochondrial dysfunction.
In humans, the data is consistent. Work by Yoshino et al. (Cell Metabolism, 2021) measured a significant reduction in muscle NAD+ levels in menopausal women compared with premenopausal women — and showed that NMN supplementation partially restored these levels.
What strikes researchers is the simultaneity of the decline with other biological markers of aging: falling NAD+ coincides with rising chronic inflammation, declining mitochondrial capacity, deteriorating sleep, and slowing DNA-repair mechanisms.
This isn't a coincidence. It's a biological cascade.
NAD+ precursors: NR and NMN
The body cannot absorb NAD+ directly by mouth. It must be synthesised inside cells from precursors.
NR (nicotinamide riboside) is a form of vitamin B3 identified as an effective NAD+ precursor by Charles Brenner in 2004. The foundational study by Trammell et al. (Nature Communications, 2016) demonstrated for the first time in humans that oral NR supplementation significantly raised blood NAD+ levels — with an excellent safety profile.
NMN (nicotinamide mononucleotide) is a precursor one step further along the biosynthesis pathway. Popularised by David Sinclair's work at Harvard, it has shown remarkable results in animal models. Human clinical studies have multiplied since 2020. To date, the body of human clinical data is more extensive for NR, with a longer track record and a better-documented safety profile — which is why we chose this precursor for the Cellular Daily composition.
CD38, inflammaging and the vicious cycle of aging
The vicious cycle is established as follows: aging generates inflammation → inflammation activates CD38 → CD38 consumes NAD+ → falling NAD+ reduces sirtuin activity → less active sirtuins favour further inflammation and cellular senescence. This mechanism explains why NAD+ decline accelerates after 50 — inflammaging is self-sustaining and amplifies the depletion.
In conclusion
NAD+ isn't a wellness trend. It is a central molecule in the biochemistry of human aging, whose progressive decline after one's thirties constitutes one of the best-documented biological markers in contemporary geroscience.
This article is published for informational and educational purposes. It does not constitute medical advice and does not replace consultation with a healthcare professional.
