NAD+ has become an important area of longevity research due to its links to cellular aging, metabolism, and lifespan outcomes observed in animal models. Some of this research has significant scientific importance, particularly at the mechanistic and preclinical levels. However, evidence indicating that NAD+ influences aging-related pathways in animals is not the same as evidence that NAD+ supplementation reverses aging in humans. Throughout the article, we maintain this distinction and also discuss how fasting fits into NAD+ biology, as fasting and caloric restriction are among the best-characterized metabolic states associated with changes in NAD+-dependent pathways.
Why does NAD+ level decline with age?
The age-related decline in NAD+ levels is one of the most consistently reported findings in this area of research. Lower NAD+ levels have been observed in the blood and numerous tissues with advancing age in animal models, and increasingly in human studies [1]. Several interrelated mechanisms may contribute to this decline.
One of the proposed mechanisms involves increased NAD+ consumption by CD38. CD38 is an NAD+-degrading enzyme, and its activity appears to increase with age. This may be due in part to the accumulation of senescent cells, which have stopped dividing but remain metabolically active and can contribute to inflammatory signaling, as well as an increase in the number of immune cells expressing CD38.
Studies on mice lacking the CD38 gene have shown that CD38 activity significantly contributes to the age-related loss of NAD+ and the associated mitochondrial dysfunction. These effects appear to involve, at least in part, pathways related to the NAD+-dependent mitochondrial enzyme SIRT3 [2].
The second mechanism is related to accumulating DNA damage and increased NAD+ consumption by PARP enzymes. DNA damage accumulates over time, and PARP proteins participate in DNA repair, using NAD+ as a substrate. Greater and more sustained repair activity can therefore increase NAD+ consumption [1].
Age-related changes in NAD+ synthesis may also contribute to this process. Some studies suggest that the activity of the NAD+ salvage pathway, including pathways regulated by the NAMPT enzyme, may decrease with age in certain tissues. If this is the case, NAD+ availability may be constrained from two sides: through increased consumption and impaired regeneration [1].
Together, these mechanisms describe a biological situation in which aging cells may produce or recover NAD+ less efficiently while simultaneously consuming more of it. This combination may partially explain the gradual decline in NAD+ levels observed with age.
Can NAD+ supplementation really „reverse” some markers of aging?
The term „reversing aging” should be separated from more specific and measurable research outcomes.
Broadly understood reversal of aging, meaning biological human rejuvenation across multiple organ systems and aging-related processes, has not been demonstrated in controlled human clinical trials. No published human study has shown that NAD+ supplementation reverses aging as a whole-organism phenomenon.
Studies on single biomarkers and biological processes related to aging are more complex.
Animal studies have provided significant results. In one influential study on mice, nicotinamide riboside increased NAD+ levels and activated the mitochondrial unfolded protein response, a cellular stress response pathway. The treatment was also associated with improved mitochondrial and muscle stem cell function, as well as an extended lifespan in the treated animals [3].
These results have significantly increased interest in NAD+ precursors in the biology of aging. However, they come from an animal model. This type of lifespan extension has not been demonstrated in humans, and studies using human lifespan as an endpoint would require very long observation periods.
Early human studies analyzed more specific biological and clinical parameters. In a phase I study involving individuals with Parkinson's disease, oral nicotinamide riboside increased NAD+ levels in the brain and was associated with minor clinical changes and changes in biomarkers related to inflammation and disease processes [4].
This represents an early signal from human research in a specific disease population. However, it should not be interpreted as evidence of a general anti-aging effect in healthy individuals. This was an early-phase study focusing primarily on safety, feasibility, biological activity, and exploratory clinical outcomes, rather than proving that NR modifies the aging process or reverses disease.
The most precise summary, therefore, is that NAD+ supplementation affected several molecular and cellular aging-related processes in animal models, while early human studies have shown biological effects in selected situations. The broadly understood reversal of aging in humans has not been confirmed.
Post and NAD+: what is this relationship really about?
The connection between fasting and NAD+ has biologically plausible and relatively well-characterized mechanistic foundations.
One of the important pathways is AMPK, which is AMP-activated protein kinase. AMPK acts as a cellular energy sensor and becomes more active when cellular energy availability drops, among other times during fasting and caloric restriction.
AMPK activation can affect NAMPT, an important enzyme in the NAD+ salvage pathway. Increased NAMPT activity may contribute to changes in NAD+ availability and the NAD+/NADH ratio, which in turn can affect NAD+-dependent enzymes such as SIRT1 [1].
This creates an interconnected metabolic pathway involving cellular energy status, AMPK signaling, NAD+ salvage, and sirtuin activity. Animal studies on caloric restriction have shown that these metabolic adaptations may help preserve or modify NAD+-related pathways that otherwise change with age [1].
This relationship therefore has a stronger mechanistic basis than many generalized claims that a specific lifestyle element „increases NAD+”.
However, significant uncertainties remain when translating these findings to humans. A large portion of the detailed mechanistic studies have been conducted in animals or cell models. Human studies directly measuring NAD+ changes in blood or tissues before and after carefully controlled fasting protocols remain limited.
As a result, current data do not allow for determining the exact post length, its frequency, or the degree of calorie restriction that would reliably cause a specific increase in NAD+ in humans. The direction of the biological relationship is fairly well supported, but the magnitude, timing, and clinical significance of this effect in humans are less clearly defined.
Sirtuins, calorie restriction and NAD+ — how are they connected?
Sirtuins represent an important mechanistic link between caloric restriction, fasting, and NAD+ metabolism.
Sirtuins require NAD+ as a substrate. Because fasting and caloric restriction can alter cellular energy-sensing mechanisms and the NAD+/NADH ratio via pathways involving AMPK and NAMPT, these metabolic states may also influence sirtuin activity [1].
This dependence is one of the reasons why sirtuins have been extensively studied in the biology of caloric restriction. In many animal models, calorie restriction has been associated with longer life or delayed development of certain age-related changes. Sirtuins were analyzed as one of the possible groups of mediators linking altered nutrient availability to subsequent effects on mitochondrial function, stress resistance, metabolism, and gene regulation.
Conceptually, the relationship can be summarized as follows: caloric restriction affects NAD+-related metabolism, which in turn can influence NAD+-dependent sirtuin activity. However, this pathway should not be interpreted as a simple linear sequence in which one intervention automatically reproduces all subsequent effects of another.
Supplementation with NAD+ precursors can, under certain conditions, increase the availability of substrates associated with NAD+, but this does not mean that it recreates the entire physiological state associated with fasting or caloric restriction.
Fasting triggers broad metabolic and hormonal changes involving insulin, glucagon, fatty acid metabolism, ketone body production, AMPK, mTOR signaling, nutrient sensing, and other pathways. Increasing NAD+ through supplementation only affects a part of this wider biological network.
For this reason, NAD+ precursor supplementation and fasting should not be treated as interchangeable strategies. Their mechanisms partially overlap, but they are not biologically equivalent.
How does NAD+ compare to other compounds promoted in the context of longevity?
NAD+ precursors belong to several groups of compounds frequently discussed in aging and longevity research. Others include resveratrol, pterostilbene, metformin, and rapamycin, although these substances act through different biological pathways and have very different evidentiary bases and regulatory contexts.
Resveratrol and pterostilbene are often discussed alongside NAD+ precursors because all of these compounds have been studied in the context of sirtuin biology. NAD+ is required as a substrate for sirtuins, whereas resveratrol and related compounds have been studied for their potential effects on sirtuin-related signaling.
This mechanistic overlap has contributed to interest in combinations of NAD+ precursors with related polyphenols. One example is the combination of nicotinamide riboside with pterostilbene analyzed in human studies [5]. However, the mere existence of a mechanistic rationale or a study of the combination does not prove that such combinations extend lifespan or provide broader anti-aging effects in humans.
Other compounds commonly associated with longevity research partially affect different pathways. Metformin is often discussed in the context of AMPK and metabolic signaling, whereas rapamycin acts primarily by inhibiting mTOR. These pathways may intersect with NAD+ and sirtuin biology, but they should not be treated as interchangeable mechanisms.
Compared to many compounds discussed in a commercial longevity context, oral NAD+ precursors such as NR and NMN have accumulated a growing body of randomized, placebo-controlled human trials indicating that they can increase NAD+ or NAD+-related metabolite levels in the blood and are generally well-tolerated over the studied short- and medium-term periods [6].
However, evidence that these compounds increase NAD+ biomarkers is not equivalent to evidence that they extend lifespan, prevent aging, or provide broad anti-aging effects in humans.
The same distinction applies to other compounds associated with longevity. None of the substances discussed here should be described as having definitively been shown to extend human life based on currently available clinical research.
A separate area of research involves companion animals. One randomized, controlled trial evaluated the combination of a novel NAD+ precursor and a senolytic compound in older dogs with mild to moderate cognitive impairment. The study demonstrated a statistically significant association with improved cognitive function as assessed by owners in the primary endpoint, as well as broader changes in parameters such as frailty, activity, and reported satisfaction levels, which were less statistically definitive [7].
This finding has translational significance because relatively few controlled studies have evaluated NAD+-related interventions specifically in aging companion animals. However, this was a single study using a combination intervention rather than NAD+ alone, and improvement was observed across all treatment groups. The researchers therefore pointed out the possibility that some of the reported changes could have been influenced by placebo-like effects, owner expectations, increased attention, or participation in the study itself.
What can be realistically expected, and what cannot?
Based on current evidence, several conclusions can be considered relatively well-founded.
NAD+ levels appear to decline with age across many tissues and biological conditions, and several mechanisms have been proposed to explain this decline, including increased CD38 activity, greater NAD+ consumption during DNA repair, and possible changes in NAD+ synthesis and salvage pathways [1,2].
Fasting and caloric restriction also have a biologically plausible and relatively well-supported link to NAD+ metabolism through pathways involving AMPK, NAMPT, the NAD+/NADH balance, and sirtuins [1].
Human studies have repeatedly shown that oral NAD+ precursors, such as NR and NMN, can increase circulating NAD+ levels or related metabolites under specific research conditions [6].
Animal studies have also shown changes in mitochondrial function, stem cell activity, cellular stress responses, and lifespan following the administration of NAD+ precursors in selected models [3]. Early human studies have identified changes in NAD+ biomarkers and exploratory clinical parameters in specific populations with diseases [4].
These results do not prove that NAD+ supplementation reverses aging in humans.
Current data also do not show that NAD+ precursor supplementation extends human lifespan, nor that it reproduces all the physiological effects of fasting or caloric restriction.
Similarly, an increase in a biomarker associated with the biology of aging does not in itself prove an improvement in healthspan, a reduction in biological age, slowed aging, or extended survival.
This area remains an active and important direction of scientific research, but currently the strongest evidence concerns mechanisms, biomarker changes, and selected experimental outcomes, rather than broad anti-aging effects in humans.
Limitations of current evidence
- The strongest results linking NAD+ supplementation to lifespan extension, improved mitochondrial function, and changes in the biology of aging come primarily from animal studies, particularly mouse models. Human studies have shown biomarker changes and safety data in the short and medium term, but have not confirmed lifespan extension or comprehensive anti-aging effects [3].
- Results concerning animal lifespans cannot be automatically translated to humans because species differ in metabolism, lifespan, disease development, NAD+ biology, dosage, and experimental conditions.
- The relationship between fasting, caloric restriction, and NAD+ metabolism has mechanistic support, but the exact dose-response relationship in humans remains poorly defined. It is not yet known how long and how frequent a fast, nor what degree of caloric restriction would be necessary to induce a specific change in NAD+ levels in humans [1].
- Human studies directly measuring NAD+ in specific tissues before and after standardized fasting protocols remain limited, so mechanistic conclusions should not be translated into precise fasting recommendations.
- Human clinical trial evidence on NAD+ precursors in specific diseases, including Parkinson's disease, remains at an early stage and should not be interpreted as evidence of broad anti-aging or disease-modifying effects [4].
- Increasing the level of NAD+ or related biomarkers does not automatically mean an improvement in biological age, healthspan, lifespan, physical fitness, cognitive function, or disease risk.
- Supplementation with NAD+ precursors should not be treated as biologically equivalent to fasting or caloric restriction, because fasting induces numerous metabolic, hormonal, and signaling changes that go beyond NAD+ metabolism.
- Evidence regarding combinations, such as NR with pterostilbene, does not confirm that NAD+ precursors combined with resveratrol or other compounds associated with longevity provide additive or stronger anti-aging effects [5].
- Comparisons with metformin, rapamycin, resveratrol, or other compounds associated with longevity are mechanistic in nature and do not constitute proof that these interventions provide equivalent or mutually interchangeable effects.
- The discussed study on cognitive function in dogs is a single controlled study using a combined intervention rather than NAD+ alone. Improvement was also noted in various treatment groups, which complicates the interpretation of the intervention-specific effect [7].
- Long-term safety and clinical outcome data in humans remain considerably more limited than short-term biomarker studies, especially when NAD+ precursors are used for years rather than weeks or months.
Disclaimer
The article is for educational and scientific research summary purposes only. It does not constitute medical advice for humans or veterinary advice for animals.
NAD+, NAD+ precursors, fasting, calorie restriction, resveratrol, pterostilbene, metformin, rapamycin, or any other compounds discussed in the context of longevity should not be interpreted as proven methods for reversing aging, extending human life, preventing diseases, or treating medical conditions, unless there is a specific approved indication and appropriate clinical evidence.
NAD+ and its precursors should not be presented as FDA- or EMA-approved treatments for aging, nor as therapies that have been shown to extend human life.
Fasting and calorie restriction are not suitable for everyone and may pose additional risks for certain individuals. Pregnant or breastfeeding women, people with diabetes, those taking glucose-lowering medications, individuals with a history of eating disorders, those who are underweight, people with certain chronic conditions, or those taking medications whose effectiveness depends on food intake should discuss fasting or significant calorie restriction with a qualified healthcare professional.
Before starting a new supplement, fasting regimen, medication, or any other intervention intended to influence aging-related processes, you should consult with a qualified healthcare professional. Questions regarding pets should be consulted with a qualified veterinarian.
References
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