Each catalytic cycle of sirtuins consumes one NAD+ molecule; the fall of NAD+ with age reduces mitochondrial efficiency.
View the study (review) →Raising NAD+ with NMN or NR improves mitochondrial function, insulin sensitivity, and physical capacity in aged animals.
View the study (preclinical) →The NAMPT enzyme of the salvage pathway may have proangiogenic activity that supports some tumors; a contradictory signal that requires precision in dosing.
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NAD+ is one of those molecules that biologists have known for more than a hundred years and that has nevertheless only recently moved to the center of the debate on biological aging; it is a cofactor, a molecule that does no work on its own but is essential for hundreds of enzymes to do theirs, and whose progressive decline with age appears to lie at the origin of many of the processes we associate with physiological deterioration: loss of mitochondrial energy, accumulation of DNA damage, chronic low-grade inflammation, desynchronization of circadian clocks, and reduced cellular repair capacity.
The human body synthesizes NAD+ from several dietary precursors: tryptophan, an essential amino acid present in animal and plant proteins; and three forms of niacin or vitamin B3, which are nicotinamide, nicotinic acid, and nicotinamide riboside, all of them called niacin equivalents; of these three, nicotinic acid is the main source of NAD+ in the body, although the precursors are distributed preferentially to different tissues, with the brain, intestine, liver, and immune system cells as the main destinations.
Two of the most relevant enzyme families in the biology of aging, the sirtuins and the poly-ADP-ribose polymerases or PARPs, are completely dependent on NAD+: sirtuins are histone deacetylases that regulate gene expression, DNA repair, mitochondrial metabolism, and the cellular stress response, and each catalytic cycle consumes one molecule of NAD+ to carry out its function; PARPs, meanwhile, are DNA repair enzymes that are massively activated when there is genomic damage and consume NAD+ in proportion to the magnitude of the damage, which under conditions of high stress can rapidly deplete the cell's reserves of this molecule.
The paradox of aging with respect to NAD+ is that precisely when it is most needed to repair accumulated damage, it is least available: NAD+ levels in skeletal muscle, skin, and brain tissue decline by thirty to sixty percent between the ages of twenty and sixty in animal and human models, and this decline does not appear to be a trivial consequence of aging but a mechanism that actively drives it, creating a vicious circle in which less NAD+ means less repair, more damage, more PARP activation, and still less NAD+.
Nicotinamide mononucleotide or NMN and nicotinamide riboside or NR are NAD+ precursors that have gained enormous attention over the last decade as possible anti-aging supplements, in part because, unlike NAD+ itself, which has difficulty crossing cell membranes directly, these smaller molecules can enter the cell and be converted into NAD+ with relative efficiency; trials in mice with NMN and NR have shown remarkable results, including improvements in glucose metabolism, mitochondrial function, insulin sensitivity, and physical capacity in aged animals, although direct extrapolation to humans requires caution.
Clinical trials in humans with NMN and NR consistently show that supplementation raises circulating levels of NAD+ and its metabolites, and some studies have reported improvements in markers of muscle function, insulin sensitivity, and cellular bioenergetics; however, translating these biochemical changes into clearly defined clinical benefits remains a work in progress that will require longer and larger trials to be confirmed.
An especially fascinating connection is the one between NAD+ and circadian clocks: NAD+ is not only a substrate for sirtuins but also for the enzyme NAMPT, which is the rate-limiting enzyme in the main NAD+ synthesis pathway and whose expression is directly regulated by the central circadian clock; this bidirectional interconnection means that irregular sleep patterns, night work, or exposure to artificial light at night not only disrupt circadian rhythm but may also affect the availability of NAD+ in critical tissues.
Information, not medical advice. Scientific evidence reflects the quality of the studies.