NAD+: the longevity molecule

If you had to pick a single molecule to embody the convergence between aging biology and performance optimization, it would be NAD+, nicotinamide adenine dinucleotide. A cofactor in several hundred enzymatic reactions, a substrate of sirtuins and PARPs, a regulator of cellular circadian rhythm: NAD+ sits at the heart of nearly every biological process associated with longevity and cellular energy.

And it is declining. Quickly. Inexorably. From your thirties onward, intracellular NAD+ levels drop by about 1 to 2% per year. By age 50, you have half as much NAD+ as you did at 20. This reduction is not trivial, it has direct biological consequences for your energy metabolism, your resistance to oxidative stress and your DNA repair capacity.

NAD+: far more than a simple cofactor

NAD+ exists in two interconvertible forms in the cell: the oxidized form (NAD+) and the reduced form (NADH). This redox couple sits at the heart of glycolysis and the mitochondrial electron transport chain, where it carries electrons extracted from energy substrates to the ETC complexes to generate ATP. Without sufficient NAD+, cellular energy production is directly compromised.

But the role of NAD+ goes far beyond energy metabolism. It is the obligatory substrate of three classes of enzymes whose importance in aging biology is considerable:

• Sirtuins (SIRT1–7): NAD+-dependent deacylases that regulate gene expression via histone deacetylation, DNA repair, mitochondrial biogenesis (via PGC-1alpha for SIRT1) and autophagy (SIRT3). David Sinclair calls them "guardians of the genome".
• PARPs (PARP1–17): poly(ADP-ribose) polymerases that detect and repair single- and double-strand DNA damage. Each activation of PARP1 consumes massive amounts of NAD+. Under chronic genotoxic stress (radiation, pollution, replication errors), overactivated PARPs deplete NAD+ reserves.
• CD38: an enzyme expressed on immune cells that hydrolyzes NAD+ into cyclic ADP-ribose (calcium signal). Its expression rises with age and inflammation, contributing to chronic depletion of tissue NAD+.

Sirtuins: longevity genes that depend on you

Sirtuins were initially discovered in yeast as longevity genes (Sir2, Silent Information Regulator 2). Their mammalian homologs (SIRT1 to SIRT7) are now central to aging biology. SIRT1 and SIRT3 are the best-studied:

SIRT1 deacetylates PGC-1alpha, activating mitochondrial biogenesis, and FOXO3, activating antioxidant genes (MnSOD, catalase). It also regulates circadian rhythm via BMAL1/CLOCK. SIRT3, located in the mitochondrion, deacetylates ETC complexes, increasing their efficiency. It also activates MnSOD, the principal mitochondrial antioxidant enzyme. Insufficient intracellular NAD+ renders both enzymes inactive, regardless of your diet or physical activity.

NMN vs NR: choosing your precursor

Two molecules have emerged as direct, bioavailable precursors of NAD+: nicotinamide mononucleotide (NMN) and nicotinamide riboside (NR). Both are modified forms of vitamin B3 that enter directly into the NAD+ biosynthesis pathway without requiring conversion through the kynurenine pathway (inefficient after age 40).

NR is converted into NMN and then into NAD+ by cells. NMN enters the pathway directly, one step closer to NAD+. Both have demonstrated their capacity to raise tissue NAD+ levels in human scientific studies. The Yoshino et al. trial (2021, Science) showed that supplementation with 250 mg/day of NMN for 10 weeks significantly increases muscle NAD+ and improves insulin sensitivity in prediabetic postmenopausal women.

Recommended dosages and forms

• NMN: 250 to 500 mg/day in the morning (liposomal or sublingual stability recommended to bypass gastric degradation)
• NR: 300 to 600 mg/day, better studied for short-term safety, slightly less effective in some indirect comparisons
• Possible pairing with resveratrol (250–500 mg), an allosteric activator of SIRT1 that improves NAD+ utilization

Raising NAD+ without supplements

Supplementation is effective, but several behavioral interventions also stimulate endogenous NAD+ biosynthesis:

• Intermittent fasting and caloric restriction activate AMPK and reduce NAD+ consumption by CD38, raising the NAD+/NADH ratio. Even a 16h fast (16:8 protocol) produces measurable effects.
• Endurance exercise increases NAD+ demand in skeletal muscle and induces compensation through upregulation of NAMPT (the rate-limiting enzyme of the biosynthesis pathway).
• Photobiomodulation reduces mitochondrial oxidative stress, which limits PARP activation, thereby preserving NAD+ for sirtuins.
• Cold exposure activates brown adipose tissue (BAT), whose metabolism is very intense and stimulates NAD+ biosynthesis in adjacent tissues.