Longevity research has propelled the scientific community to concentrate on interventions that do more than simply add years to the end of life; they aim to add life to years, effectively prolonging the healthy phase of midlife and delaying the debility and functional decline observed in the final 10-20 years of a person’s life
Longevity research has evolved from its early focus on merely extending lifespan to a broader, more impactful goal: extending healthspan – the period of life spent in good health. While lifespan measures the number of years lived, healthspan emphasizes quality, encompassing physical, mental, and emotional health (Box 1). Recognizing this distinction has propelled the scientific community to concentrate on interventions that do more than simply add years to the end of life; they aim to add life to years, effectively prolonging the healthy phase of midlife and delaying the debility and functional decline observed in the final 10-20 years of a person’s life.
This shift has catalyzed the development of personalized health interventions, which leverage advancements in genetic testing, biomarker analysis, microbiome science, wearable technologies, and novel supplements to tailor health strategies to individual needs. Unlike one-size-fits-all approaches, personalized methods recognize the inherent variability in human biology and behavior. For instance, factors such as genetic predispositions, lifestyle, and environmental exposures can significantly impact how each person responds to diet, exercise, and supplementation strategies.
The biology of aging: Mechanisms that shape longevity
Understanding the biology of aging involves examining the cellular and molecular processes that drive senescence and functional decline. These processes are shaped by both the internal accumulation of cellular damage and external environmental factors. Over time, disruptions in repair mechanisms accumulate, leading to the progressive deterioration of physiological systems and the emergence of age-related diseases. Many of these pathways have been identified as therapeutic targets for interventions aimed at extending healthspan.
Hallmarks of aging
One key feature of aging is genomic instability, which arises from the accumulation of DNA damage, caused by environmental stressors such as ultraviolet radiation and internal factors such as reactive oxygen species (ROS). While DNA repair mechanisms work to maintain genomic integrity, their efficiency diminishes with age. This leads to an increased burden of mutations and chromosomal abnormalities, impairing cellular function and elevating the risk of diseases such as cancer.
Similarly, telomere attrition—shortening of the protective caps at the ends of chromosomes—limits a cell’s ability to divide. When telomeres become critically shortened, cells either enter a state of replicative senescence or undergo programmed cell death, reducing tissue regenerative capacity.
Mitochondrial dysfunction is another major hallmark of aging. Mitochondria, the cellular powerhouses, produce energy in the form of ATP and play roles in cell signaling and metabolic regulation. As organisms age, mitochondrial efficiency declines, resulting in reduced energy production and increased generation of ROS. This exacerbates oxidative damage to cellular components and contributes to chronic inflammation, which is closely linked to aging and many age-related diseases.
In parallel, aging disrupts the maintenance of proteostasis, the delicate balance of protein synthesis, folding, and degradation. The accumulation of misfolded or aggregated proteins is particularly detrimental in tissues with limited regenerative capacity, such as the brain, and is associated with neurodegenerative conditions like Alzheimer’s disease.1
Age-related NAD+ decline
NAD+ (nicotinamide adenine dinucleotide) is a vital coenzyme molecule in metabolic reactions and serves as a substrate for enzymes such as sirtuins and poly(ADP-ribose) polymerases (PARPs). These enzymes are crucial for DNA repair, mitochondrial function, and cellular stress responses. However, NAD+ levels decline with age, impairing these processes and exacerbating mitochondrial dysfunction and inflammation. Furthermore, NAD+-consuming enzymes like CD38 become hyperactive with age, further depleting NAD+ pools. Restoring NAD+ through targeted supplementation or by modulating its metabolic pathways has demonstrated promise in counteracting age-related health decline.2
Metabolic regulators
Key molecular regulators shed light on the mechanisms driving aging. Sirtuins, a family of NAD+-dependent enzymes, regulate a variety of processes, including mitochondrial biogenesis, stress resistance, and autophagy. Their activity connects NAD+ availability to pathways associated with longevity.
Similarly, mTOR (mechanistic target of rapamycin), a nutrient-sensing kinase, integrates signals related to growth and energy status to regulate metabolism and cell proliferation. Inhibition of mTOR through caloric restriction or pharmacological agents has demonstrated lifespan extension across several species. Complementing this is the role of AMPK (AMP-activated protein kinase), a metabolic sensor that responds to low energy states by enhancing mitochondrial efficiency and promoting autophagy.3
Aging pathways are not isolated: The bigger picture
These pathways cannot be considered in isolation since anything that impacts one will affect the others in a cascade of reactions. Therapies that can positively modulate all of these pieces are more likely to improve multiple hallmarks of aging, preserving cellular function and ultimately extending the healthy years of life.
Clarity through data: Taking the guesswork out of health decisions
As our understanding of aging deepens and technology evolves, new strategies for addressing age-related decline are emerging. Genetic testing provides insight into individual biological predispositions, while biomarker analysis offers a real-time picture of metabolic health and responses to interventions. Continuous monitoring of heart rate variability and glucose levels gives more insight into how lifestyle changes affect metabolism. Multiomics platforms, which integrate genetic, proteomic, and metabolomic data, further refine our understanding of the complex interactions shaping longevity.
These tools generate enormous amounts of data, and translating it into useful and actionable insights is key. Artificial intelligence (AI) and machine learning (ML) are essential for analyzing this complex data, identifying patterns and relationships between biomarker fluctuations, lifestyle factors, and long-term health outcomes.
Personalized NAD+ strategies: An approach for healthy aging
NAD+ is central to longevity research because of its vital role in cellular health and its involvement in diverse, essential processes, including energy metabolism, DNA repair, and circadian rhythms. NAD+ has been recognized as a longevity biomarker in mice because its levels are influenced by lifespan-extending interventions.4 NAD+ levels are dynamic, responding to physiological and environmental factors, and generally reflect overall health status.
Low levels are linked to aging-related diseases, sedentary behavior, and excessive calorie intake, while higher levels are associated with longevity-promoting habits like exercise and caloric restriction. This positions NAD+ as both a potential biomarker and a target for therapies aimed at extending healthspan.
Individual variability in NAD+ supplementation outcomes
The most common approach to boosting NAD+ levels is through supplementation with its precursors, nicotinamide mononucleotide (NMN) and nicotinamide riboside (NR). Although preclinical studies consistently show benefits such as enhanced cognitive function, improved metabolic health, and reduced age-related decline, the results in human studies have been more variable than expected.
The inconsistent results of NMN supplementation in humans likely result from individual variations in NAD+ metabolism. Even in carefully controlled studies, blood NAD+ responses to NMN or NR supplementation vary widely. For example, Kuerec et al. reported the CV of blood NAD levels ranged from 29.2% to 113.3% within groups receiving NMN.5 Several factors contribute to this variability:
- Genetic Differences:
- Gene expression related to NAD+ synthesis and consumption varies between individuals, influencing their response to NAD+ precursor supplementation. Wang et al. found that individuals with higher expression of NAD+ biosynthetic enzymes (IDO2, NAPRT, NMNAT2, NAMPT) showed greater NAD+ increases after NMN supplementation, while those with higher expression of NAD+-consuming enzymes (CD38, SIRT4, PARPs) had minimal changes.6
- Gut Microbiome:
- The gut microbiome has a significant impact on the metabolism and bioavailability of NAD+ precursors. Variations in gut microbiota composition can significantly impact the absorption, conversion, and utilization of these compounds, thereby influencing individual NAD+ levels and responses to supplementation.2
- Sex and Hormones:
- Baseline NAD+ levels may differ between sexes, with some research suggesting men have higher levels than women. In postmenopausal women, NAD+ fluctuations indicate that sex hormones may regulate NAD+ metabolism.7
- Lifestyle Factors:
- Diet, exercise, sleep, and environmental factors all impact NAD+ levels. Exercise, for example, can mitigate age-related NAD+ decline.8
In a post-hoc analysis, Kuerec et al. examined how changes in NAD+ levels, rather than dosage of NMN administered, influenced treatment outcomes. The initial study results suggested that only high doses of NMN improved physical performance. However, the post-hoc analysis showed a strong link between how much each person’s NAD+ levels increased and their performance improvement, regardless of the dose they took. This suggests that the extent of NAD+ change is an important consideration when evaluating efficacy.5
Navigating a personalized NAD+ boosting approach
Personalizing NAD+ supplementation requires a well-structured approach that is practical and sustainable over time. A major challenge in evaluating NAD+ boosting strategies is the lack of consensus on deficient, optimal, or elevated NAD+ levels. It is generally accepted that NAD+ levels are higher in younger, healthier people, and are lower with advanced age and disease. One study found that individuals aged 20–50 had significantly higher NAD+ levels than those aged 50–85, with a more pronounced decline in men (from ~44 μM to ~26 μM) compared to women (from ~33 μM to ~25 μM).6 However, these values and the rate of decline are not consistent across all studies. More clinical trials are needed to establish clear relationships between NAD+ levels and specific health outcomes.
Although there is no definitive “healthy” NAD+ reference range, NAD+ measurements remain highly valuable, providing a quantifiable starting point for assessing the effectiveness of any intervention and developing a tailored approach that fits an individual’s unique biology and lifestyle.
Numerous studies offer insights into common dosage protocols and typical NAD+ responses. For example, dose-dependent increases in NAD+ levels have been observed with both NR and NMN supplementation. In overweight adults (ages 40-60), two weeks of NR supplementation increased NAD+ levels from a baseline of 21-23 μM to 27 μM (100 mg/day), 33 μM (300 mg/day), and 51 μM (1000 mg/day).9 Similarly, in older adults (average age 57), one month of NMN supplementation resulted in average NAD+ levels of 23.8 μM (placebo), 41.7 μM (500 mg/day), and 58.8 μM (1000 mg/day).6 Throughout the literature, moderate increases in NAD+ (40-60%) are often seen in trials using NMN or NR at 250-300 mg/day.
Optimizing NAD+ levels through a multi-pathway strategy
NAD+ levels in the body are maintained by a dynamic balance between its production and breakdown.
To support NAD+ synthesis, supplementing with precursors provides the necessary building blocks to sustain its production. Equally important is minimizing NAD+ degradation, which helps preserve existing NAD+ levels and maintain cellular function.
Key factors contributing to NAD+ depletion during aging include the overactivation of NAD+-consuming enzymes, chronic inflammation, and the accumulation of senescent cells. Research has identified several compounds that can help regulate these processes to support NAD+ maintenance.
Inhibiting NAD+ consuming enzymes NAD+-consuming enzymes play essential roles in cellular function but can become overactive with age, leading to NAD+ depletion. CD38, a major NAD+ consumer, is particularly implicated in this decline, as its activity increases in response to chronic inflammation. Preclinical studies show that flavonoids like apigenin, quercetin, and luteolin effectively inhibit CD38, helping to reduce NAD+ degradation and preserve cellular NAD+ levels.10 Similarly, PARP-1, another NAD+ consumer, can become hyperactivated during cellular stress, contributing to NAD+ depletion and chronic disease development. Quercetin and fisetin have been shown to inhibit PARP-1 in human cell models, preventing excessive NAD+ consumption.11
Targeting senescent cells
Recent studies have established a link between declining NAD+ levels and the accumulation of senescent cells, a key hallmark of aging. This relationship is largely driven by chronic inflammation and the secretion of the senescence-associated secretory phenotype (SASP), a mix of pro-inflammatory cytokines, chemokines, and proteases. SASP not only promotes tissue damage and inflammation but also upregulates CD38 expression, further accelerating NAD+ depletion. Targeting senescent cells has emerged as a promising strategy to resolve this cycle.
Several bioactive compounds, including fisetin, quercetin, apigenin, spermidine, and berberine, exhibit senolytic properties, either by selectively eliminating senescent cells or by suppressing SASP secretion. These compounds have shown efficacy in preclinical models by modulating pathways involved in inflammation, cellular repair, and NAD+ metabolism, highlighting their potential role in promoting healthy aging.12, 13, 14, 15
Implications for “Non-Responders”
Reducing NAD+ degradation may be especially beneficial for individuals who show minimal response to NAD+ precursor supplementation (“non-responders”). This reduced efficacy may be due to elevated levels of NAD+-consuming enzymes or chronic inflammation, both of which can offset the benefits of increased NAD+ availability. Combining NAD+ precursors with strategies that target degradation pathways offers a comprehensive approach to maintaining NAD+ homeostasis and promoting healthy aging.
Addressing the impact of lifestyle factors
As research on NAD+ dynamics advances, it is clear that maintaining NAD+ homeostasis is a complex, multifaceted process. Simply increasing precursor availability is not always sufficient, as lifestyle and environmental factors play a significant role in regulating NAD+ balance. Diet, exercise, inflammation, and health status influence the cellular environment, affecting the rate of NAD+ synthesis and degradation. Monitoring and addressing these factors is necessary for optimizing NAD+ boosting strategies and achieving meaningful improvements in healthspan.
Caloric restriction (CR) has consistently demonstrated lifespan extension (25-60%) in various model organisms, through NAD+ preservation and sirtuin activation.16 CR achieves this by reducing NADH, an inhibitor of sirtuins, and increasing the expression of NAMPT, a key enzyme in NAD+ biosynthesis. This, in turn, supports sirtuin-mediated processes, including DNA repair and mitochondrial biogenesis, contributing to cellular health and longevity.
Conversely, excessive calorie intake and obesity are associated with decreased NAD+ levels and reduced NAMPT expression in key metabolic tissues, including the muscle, adipose, and liver.17 For example, one study reported a 33% decline in muscle NAD+ levels after 56 days on a high-fat diet.15 Obese individuals have lower NAD+ and sirtuin levels and higher PARP activity, but weight loss can restore these levels.18
Physical activity has a substantial effect on NAD+ metabolism. Studies have shown that athletes have twice the NAMPT levels in skeletal muscle compared to sedentary individuals, and a three-week exercise program can double NAMPT levels even in previously sedentary participants.19 Aging is associated with a decline in NAD+ levels, with the most pronounced reductions observed in individuals with physical impairments. However, older adults who exercise regularly maintain NAD+ levels comparable to those of younger individuals.20 Both aerobic and resistance exercise have been shown to increase NAMPT, improve mitochondrial function, and enhance muscle health and physical performance across age groups.21
Circadian rhythms significantly influence mammalian physiology and behavior by tightly coupling metabolism to the body’s internal clock. The core clock regulator, SIRT1, requires NAD+, which is generated by the enzyme NAMPT. Both NAMPT and NAD+ levels cycle over 24 hours, driven by the circadian clock. These fluctuating NAD+ levels, in turn, influence SIRT1 activity, creating a feedback loop that shapes the body’s internal rhythms. Sleep deprivation and circadian disruption suppress NAMPT activity, resulting in lower NAD+ levels. Conversely, regular sleep and consistent light-dark cycles support NAMPT activity. Obesity disrupts this system by blunting the circadian fluctuations of NAD+.22 Aging also contributes to reduced NAMPT activity, which is exacerbated by poor sleep, ultimately leading to lower NAD+ levels and impaired circadian function.23
