Does blood NAD⁺ decline with age? What the latest science tells us
Commentary by Dr Toby Chin, Chief Scientific Officer, XANDRO LAB, Nov 2026
Disclaimer: This article presents the author’s scientific interpretation of published research and reflects the evidence available at the time of writing. It has not undergone independent peer review and is intended for scientific discussion and educational purposes, not as medical advice or a recommendation for any specific treatment or supplementation.
NAD⁺ and aging: what does the latest science actually tell us?
Nicotinamide adenine dinucleotide (NAD⁺) is an essential coenzyme involved in cellular energy metabolism, DNA repair, and the regulation of cellular stress responses. Its importance in maintaining normal cellular function has attracted considerable scientific interest, particularly in longevity research, where changes in NAD⁺ metabolism have been implicated in several biological processes associated with aging. Previous studies have reported declining NAD⁺ concentrations in certain tissues with increasing chronological age, providing a scientific rationale for investigating whether NAD⁺ precursor supplementation could support physiological function during aging.1-3
However, a recent study published in Nature Metabolism has challenged the widely held assumption that NAD⁺ concentrations consistently decline with age. Examining more than 300 participants across seven human cohorts, researchers found no consistent relationship between chronological age and whole-blood NAD⁺ concentrations.4 These findings have prompted renewed discussion regarding the relationship between NAD⁺ metabolism, aging, and the potential applications of NAD⁺ precursors such as nicotinamide mononucleotide (NMN). Understanding their significance requires careful consideration of how NAD⁺ is measured, how its metabolism differs between tissues, and what existing human clinical studies have demonstrated.
NAD⁺ and its relationship with aging
NAD⁺ participates in numerous biochemical reactions essential for normal cellular function. Its primary role involves facilitating metabolic reactions required for the production of adenosine triphosphate (ATP), the principal energy currency of cells. NAD⁺ also serves as a substrate for enzymes involved in cellular maintenance, including sirtuins and poly (ADP-ribose) polymerases (PARPs), which participate in metabolic regulation, DNA damage responses, and cellular stress signaling.5
Given these functions, changes in NAD⁺ availability may influence several physiological processes associated with aging. Previous human investigations have reported lower NAD⁺ concentrations in tissues such as the skin, brain, and skeletal muscle among older individuals, suggesting that NAD⁺ metabolism may undergo age-associated alterations.1-3 These observations have contributed to growing interest in NAD⁺ metabolism as a potential target for interventions intended to support healthy aging.
Nevertheless, NAD⁺ concentrations are regulated through several interconnected processes, including synthesis, consumption, and recycling. These processes vary according to tissue type, metabolic requirements, and physiological conditions. Consequently, measurements obtained from individual tissues may provide different insights into NAD⁺ metabolism, particularly when investigating biological changes associated with aging.
New findings challenge the assumption of declining NAD⁺
In their recent study, Trętowicz and colleagues investigated the relationship between chronological age and whole-blood NAD⁺ concentrations across seven human cohorts. Their analysis, involving more than 300 participants, found no consistent evidence that whole-blood NAD⁺ concentrations decrease with increasing age.4 These findings challenge the interpretation of declining circulating NAD⁺ as a universal feature of aging and raise important questions regarding the use of blood NAD⁺ concentrations as a biomarker.
An important consideration is the distinction between circulating NAD⁺ concentrations and NAD⁺ metabolism within individual tissues. Whole blood contains different cellular populations, particularly red blood cells, whose metabolic characteristics differ substantially from those of organs such as the brain and skeletal muscle. Consequently, NAD⁺ concentrations measured in whole blood may provide limited information regarding metabolic changes occurring within specific tissues.
The researchers also demonstrated that NAD⁺ measurements were influenced by sample processing and storage conditions. Conventional freezing procedures were associated with reductions in measurable NAD⁺ concentrations, highlighting the sensitivity of NAD⁺ to pre-analytical handling and the importance of standardized measurement procedures.4 Such methodological differences may contribute to variability between studies and complicate comparisons of NAD⁺ concentrations across different populations.
Collectively, these observations suggest that age-associated changes in NAD⁺ metabolism may be tissue-specific, with whole-blood measurements providing an incomplete representation of NAD⁺ availability throughout the body. The findings therefore refine current understanding of NAD⁺ biology and emphasize the importance of selecting appropriate biological samples when investigating its relationship with aging.
Implications for NAD⁺ precursor supplementation
Interestingly, the same study that questioned the relationship between whole-blood NAD⁺ concentrations and chronological age also demonstrated that supplementation with nicotinamide riboside (NR), an NAD⁺ precursor, significantly increased circulating NAD⁺ concentrations.4 This observation is particularly relevant because it demonstrates that NAD⁺ metabolism remains responsive to precursor supplementation, irrespective of whether circulating concentrations consistently decline with age.
These findings are consistent with previous human clinical trials demonstrating that supplementation with NAD⁺ precursors, including NMN and NR, can increase circulating NAD⁺ concentrations.6-8 The available evidence therefore establishes that NAD⁺ precursor supplementation produces measurable biochemical responses in humans, providing a foundation for investigating its potential physiological applications.
However, circulating NAD⁺ concentrations may not accurately represent changes within individual tissues. Clinical studies examining skeletal muscle have reported variable responses following NAD⁺ precursor supplementation, suggesting that tissue-specific regulation influences the extent to which supplementation alters NAD⁺ availability.9-11 Furthermore, increases in circulating NAD⁺ concentrations do not necessarily establish corresponding improvements in physiological function, making clinical outcomes an important consideration when evaluating supplementation.
The significance of NAD⁺ precursor supplementation therefore extends to understanding whether changes in NAD⁺ metabolism can produce measurable benefits in physiological processes relevant to healthy aging. This question has become an increasingly important focus of human clinical research investigating NMN.
Clinical evidence supporting NMN supplementation
Human clinical studies have demonstrated that NMN supplementation can influence NAD⁺ metabolism, with selected trials reporting improvements in physical performance and metabolic function. In a randomized controlled trial involving 80 middle-aged adults, supplementation with 300-900 mg/day of NMN for 60 days improved six-minute walking distance, suggesting potential benefits for functional exercise capacity.12 Additional studies have reported improvements in selected measures of aerobic exercise performance and walking ability.13,14 Furthermore, supplementation with 250 mg/day of NMN for 10 weeks improved skeletal muscle insulin sensitivity in postmenopausal women with prediabetes, suggesting potential metabolic benefits in specific populations.9
Despite these encouraging findings, clinical outcomes remain variable. Systematic reviews and meta-analyses have reported limited or inconsistent improvements in muscle strength, muscle mass, and conventional measures of glucose and lipid metabolism.15-17 Furthermore, most clinical trials have investigated NMN supplementation over relatively short periods, limiting conclusions regarding sustained physiological benefits. Although NMN has generally demonstrated favorable short-term tolerability, longer-duration studies are required to establish its long-term safety and efficacy.18
Overall, the available evidence supports continued investigation into NMN supplementation, particularly its potential applications in maintaining physical performance and metabolic function during aging. Larger, longer-duration clinical trials will be important for determining the consistency and clinical significance of these preliminary findings.
NAD⁺ supplementation and the importance of healthspan
Longevity research increasingly recognizes the importance of healthspan, defined as the period of life spent maintaining good health, physical function, and independence. Although lifespan describes the total duration of life, healthspan provides a broader perspective on aging by considering the preservation of physiological function and quality of life.
Within this context, NAD⁺ metabolism represents an important area of investigation because of its involvement in cellular energy production, metabolic regulation, and cellular maintenance. Preclinical studies have demonstrated that long-term NMN supplementation can improve selected measures of physiological function in aging mice, providing a biological rationale for investigating similar outcomes in humans.19 Although these observations cannot be directly extrapolated to human aging, they support continued research into the potential applications of NAD⁺ precursor supplementation.
The preliminary improvements in physical performance and metabolic function reported in selected human NMN trials are relevant to this broader objective. Maintaining mobility, exercise capacity, and metabolic health may contribute to functional independence during aging, although further research is required to determine whether the observed benefits can be sustained over longer periods.
Future clinical studies involving larger populations, extended intervention periods, and clinically meaningful measures of physiological function will be essential for clarifying the potential role of NMN in supporting healthspan. Such investigations may also help identify individuals who are more likely to benefit from NAD⁺ precursor supplementation.
Conclusion
The recent findings published in Nature Metabolism challenge the assumption that whole-blood NAD⁺ concentrations consistently decline with chronological age. These observations highlight important differences between circulating NAD⁺ measurements and tissue-specific metabolism, while reinforcing the need for reliable analytical methods when investigating the relationship between NAD⁺ and aging.
Importantly, human clinical trials have established that NAD⁺ precursor supplementation can increase circulating NAD⁺ concentrations, with selected NMN studies reporting encouraging improvements in physical performance and metabolic function. Although clinical outcomes remain variable and longer-term evidence is required, the existing findings provide a meaningful scientific foundation for continued investigation.
The potential applications of NMN are therefore best considered within the broader context of maintaining physiological function throughout aging. As research continues to clarify the relationship between NAD⁺ metabolism and healthspan, further clinical investigations may help establish how NAD⁺ precursor supplementation can contribute to strategies aimed at supporting healthier aging.