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Getting to Know NAD+: Why It Drops After 40 and What Actually Restores It
Healthy Aging · Cellular Health
As we get older, our bodies change in many ways. One molecule that has attracted a lot of attention in healthy-aging research is NAD⁺.
NAD⁺ (nicotinamide adenine dinucleotide) is an important molecule found in our cells. It helps with energy production, mitochondrial metabolism, DNA repair, and cellular signaling. Researchers are interested in NAD⁺ because aging and metabolic stress may affect how our bodies make and use it.
However, scientists do not yet fully understand how much NAD⁺ declines with age in humans. Evidence suggests that NAD levels decline not only with age, but also with stress. (1,2) So what does that mean for NAD⁺ after 40, and what can you actually do about it?
How to Support NAD⁺ Levels
The answer is more complicated than simply taking an NAD⁺ supplement. Our bodies constantly make, use, break down, and recycle NAD⁺ through several connected metabolic pathways. That means there are several places to intervene, starting with the most basic one.
How Can NAD⁺ Be Increased?
Exercise: one of the basics. Exercise is one of the most important ways to support overall metabolic and mitochondrial health. Both aerobic exercise and resistance training can influence NAD⁺ metabolism.
Exercise also has a long track record of benefits beyond NAD⁺. Regular physical activity can improve cardiovascular fitness, insulin sensitivity, muscle strength, and physical function.
In other words, you don't need a complicated supplement routine to support the systems NAD⁺ is involved in. Moving your body regularly is a strong foundation. (3) Beyond movement, the body also needs the raw materials to build NAD⁺, which is where diet and precursors come in.
Vitamin B3
Vitamin B3 provides the building blocks the body uses to make NAD⁺. Two forms, niacin and nicotinamide, both contribute to NAD⁺ production. Getting enough matters, but more isn't necessarily better: high doses of supplemental niacin can cause side effects, which is why the National Institutes of Health lists an upper intake level of 35 mg per day for adults. (4)
Nicotinamide Riboside (NR)
NR is an NAD⁺ precursor, meaning the body can use it as a starting material in NAD⁺ metabolism, and it has been studied in human clinical trials. One randomized, placebo-controlled trial found that long-term NR supplementation was well tolerated and increased NAD⁺ metabolism in healthy older adults. (5)
Nicotinamide Mononucleotide (NMN)
In one randomized, double-blind, placebo-controlled trial, people taking 250 mg/day of NMN for 12 weeks had a significant increase in whole-blood NAD⁺ levels. (6) Another randomized trial in older adults also found increases in blood NAD⁺ and NAD-related metabolites at 250 mg/day for 12 weeks, with some secondary improvements reported in walking time and sleep quality. (7)
These findings are interesting, but there is an important distinction: increasing an NAD⁺ measurement is not the same thing as proving that a supplement slows aging or extends lifespan. That distinction matters even more when we look at NAD⁺ itself taken by mouth.
What About Taking NAD⁺ Orally?
This is where things get especially interesting. Taking NAD⁺ itself by mouth is different from taking an NAD⁺ precursor such as NR or NMN.
NAD⁺ is a relatively complex molecule. We should not automatically assume that NAD⁺ swallowed in a supplement travels through the digestive system unchanged and then enters every cell intact. Instead, NAD-related molecules can be broken down and processed into smaller compounds, which can then take part in the body's NAD⁺ production and recycling pathways.
Research into NAD metabolism shows that NAD precursors taken orally can be changed by the body before contributing to NAD⁺ production. For example, research found that oral NR was extensively metabolized, and its contribution to the body's NAD synthesis involved conversion through other NAD-related metabolites. However, this study was performed in mice, and its findings should not automatically be assumed to work exactly the same way in humans. (8)
A Simple Way to Picture the Process
- Oral NAD⁺ → metabolic breakdown
- → NAD-related metabolites
- → cellular uptake and recycling
- → intracellular NAD⁺
The key idea is that oral NAD⁺ may not have to enter cells as an intact NAD⁺ molecule to potentially affect cellular NAD⁺ availability.
Human Evidence for Oral NAD⁺
A 2026 randomized controlled trial provides some of the most direct human evidence so far. Researchers studied a specially formulated oral NAD⁺ product called LNAD⁺ in healthy adults between the ages of 45 and 75. Participants took the product for five days. (9)
The researchers reported a 53% increase in intracellular NAD in whole blood compared with placebo on Day 6. At the same time, plasma NAD did not increase significantly. The assumption is that since NAD did not stay in the blood, it crossed into the cells. (9) In simple terms, the administered NAD⁺ appeared to interact with the body's metabolic pathways rather than simply sitting unchanged in the bloodstream. (9)
That finding is interesting because it suggests that a specially formulated oral NAD⁺ product may increase NAD⁺ within the cells without causing a large increase in NAD⁺ circulating in plasma (the fluid portion of blood that carries proteins, hormones, and nutrients).
But We Still Don't Know Much
- This was a small, short-term study involving one specific formulated product. It does not show that every oral NAD⁺ supplement will produce the same results.
- It also does not establish long-term benefits for aging, longevity, cognition, or disease prevention. (9)
What Does This Mean for NAD⁺ After 40?
This is where it helps to separate two different questions: Can we raise NAD⁺ levels? And: Does raising NAD⁺ improve health or slow aging? Those are not the same question.
A 2025 review concluded that evidence for a major age-related decline in NAD⁺ in humans remains limited. The review also found that human clinical trials of NAD⁺ precursors have shown biochemical changes, but evidence of major clinical benefits remains limited. (1) A 2026 systematic review reached a similar conclusion, finding that NR and NMN consistently affect NAD-related biomarkers in humans, while improvements in functional and health span outcomes have been inconsistent. (2)
So, for now, view NAD⁺ supplementation as an emerging area of healthy-aging research rather than an established anti-aging treatment. That still leaves plenty you can do today.
A Practical NAD⁺ Strategy
If you're interested in supporting healthy NAD⁺ metabolism, the research points toward a bigger picture rather than a single magic pill.
Exercise Consistently
Combine resistance training with aerobic activity.
Get Enough Vitamin B3
A balanced diet can provide vitamin B3. Foods rich in vitamin B3 include meat, fish, pork, legumes, nuts, and seeds.
Support Metabolic Health and Sleep
Metabolic health and healthy sleep–wake rhythms are closely interconnected with cellular processes involving NAD⁺, an important cofactor in metabolism and the regulation of circadian rhythms. (10)
Watch the Oral NAD⁺ Research
The 2026 LNAD⁺ trial provides early human evidence that a specially formulated oral NAD⁺ product can increase intracellular NAD through a process accompanied by downstream NAD metabolism. (9)
For people who want NAD⁺ support as part of a broader cellular-energy routine, some formulas pair NAD with other mitochondrial nutrients. TWC's Recharge, for example, combines NAD with methylene blue and PQQ, and fits best alongside, not in place of, the exercise, nutrition, and sleep habits above.
The Bottom Line
New research suggests that oral NAD⁺ itself may increase intracellular NAD, at least when delivered in lyophilized (freeze-dried) form. The evidence is consistent with metabolic processing and recycling playing an important role. (9)
The science is promising, but it is still developing. For now, NAD⁺ is best understood as one piece of the much larger puzzle of healthy aging, not a proven shortcut to turning back the biological clock. Consistent movement, adequate vitamin B3, and steady sleep and metabolic habits remain the foundation after 40.
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References
- Vinten KT, Trętowicz MM, Coskun E, van Weeghel M, Cantó C, Zapata-Pérez R, Janssens GE, Houtkooper RH. NAD+ precursor supplementation in human ageing: clinical evidence and challenges. Nat Metab. 2025 Oct;7(10):1974-1990. doi: 10.1038/s42255-025-01387-7. PMID: 41083806.
- Gallagher, C., & Emmanuel, O. O. (2026). NAD⁺ supplementation for anti-aging and wellness: A PRISMA-guided systematic review of preclinical and clinical evidence. Ageing Research Reviews. https://doi.org/10.1016/j.arr.2026.103057
- White AT, Schenk S. NAD(+)/NADH and skeletal muscle mitochondrial adaptations to exercise. Am J Physiol Endocrinol Metab. 2012 Aug 1;303(3):E308-21. doi: 10.1152/ajpendo.00054.2012. PMID: 22436696; PMCID: PMC3423123.
- National Institutes of Health, Office of Dietary Supplements. (2022, November 18). Niacin: Fact sheet for health professionals.
- Martens, C. R., Denman, B. A., Mazzo, M. R., Armstrong, M. L., Reisdorph, N., McQueen, M. B., Chonchol, M., & Seals, D. R. (2018). Chronic nicotinamide riboside supplementation is well-tolerated and elevates NAD⁺ in healthy middle-aged and older adults. Nature Communications, 9, 1286. https://doi.org/10.1038/s41467-018-03421-7
- Okabe, K., Yaku, K., Uchida, Y., Fukamizu, Y., Sato, T., Sakurai, T., Tobe, K., & Nakagawa, T. (2022). Oral administration of nicotinamide mononucleotide is safe and efficiently increases blood nicotinamide adenine dinucleotide levels in healthy subjects. Frontiers in Nutrition, 9, 868640. https://doi.org/10.3389/fnut.2022.868640
- Morifuji, M., Higashi, S., Ebihara, S., & Nagata, M. (2024). Ingestion of β-nicotinamide mononucleotide increased blood NAD levels, maintained walking speed, and improved sleep quality in older adults in a double-blind randomized, placebo-controlled study. GeroScience, 46(5), 4671–4688. https://doi.org/10.1007/s11357-024-01204-1
- Chellappa, K., McReynolds, M. R., Lu, W., Zeng, X., Makarov, M., Hayat, F., Mukherjee, S., Bhat, Y. R., Lingala, S. R., Shima, R. T., Descamps, H. C., Cox, T., Ji, L., Jankowski, C., Chu, Q., Davidson, S. M., Thaiss, C. A., Migaud, M. E., Rabinowitz, J. D., & Baur, J. A. (2022). NAD precursors cycle between host tissues and the gut microbiome. Cell Metabolism, 34(12), 1947–1959.e5. https://doi.org/10.1016/j.cmet.2022.11.004
- Kornilov, S. A., Hastings, W. J., McGrath, L. F., Leitz-Langan, M., Magis, A. T., Coppess, S. M., & Komac, W. (2026). Oral LNAD⁺ rapidly elevates whole blood intracellular NAD and metabolic flux without elevating plasma NAD: Evidence from a randomized controlled trial. GeroScience. https://doi.org/10.1007/s11357-026-02399-1
- Levine DC, Ramsey KM, Bass J. Circadian NAD(P)(H) cycles in cell metabolism. Semin Cell Dev Biol. 2022 Jun;126:15-26. doi: 10.1016/j.semcdb.2021.07.008. PMID: 34281771; PMCID: PMC8761220.
Author
This content is for information only and not to be used as medical advice. Consult with your care provider for your healthcare needs before starting any supplement or other medical interventions.
