The Key to Aging: Understanding NAD, NMN, and NAD Injections

💡 At a Glance

· NAD (coenzyme I) is a core coenzyme responsible for energy metabolism, DNA repair, and aging regulation in all cells, and its level drops to about half between the 20s and 50s.

· When NAD decreases, the functions of sirtuins (aging-regulating proteins) and PARP (DNA repair enzymes) decline, leading to collagen breakdown, fine lines, and reduced elasticity.

· The oral supplement with the strongest evidence is NMN. Taking 250 mg per day for 12 weeks significantly increased blood NAD levels (Igarashi et al., 2022).

· NAD intravenous injections are popular, but even with intravenous administration, the increase in blood NAD is limited and discomfort during infusion is common, so their efficiency remains debated.

· Lifestyle habits such as exercise, sleep, and sun protection also directly contribute to maintaining NAD.

NAD (NAD+, Nicotinamide Adenine Dinucleotide, coenzyme I, coenzyme I) is a coenzyme (an assisting substance that helps enzymes work) found inside every living cell in the body. Recently, in the anti-aging field, it has been called the “switch of aging,” and interest in NMN supplements and NAD intravenous injections is growing rapidly. Yet the criteria for choosing between them are often mixed up. In this article, we summarize why NAD is important for aging and skin, along with three management methods based on the research evidence available so far.

Why is NAD directly linked to skin aging?

The reason NAD is important is not simply because it creates energy, but because two types of enzymes that directly regulate aging use NAD as fuel.

The first is sirtuin. Sirtuins such as SIRT1 and SIRT6 are “NAD-dependent proteins” that only work when NAD is available. They suppress the enzyme that breaks down collagen (MMP-1), protecting collagen, which is the basis of skin elasticity, and they also help calm inflammatory signals (NF-κB).

The second is the group of DNA repair enzymes called PARP. Every day, skin DNA is damaged by ultraviolet light, air pollution, and oxidative stress, and PARP immediately repairs that damage. However, PARP also uses NAD to work, so when NAD is insufficient, repair slows and damage accumulates.

The problem is that NAD decreases with age. Multiple studies report that in humans, intracellular NAD drops to about half between the 20s and 50s. As NAD decreases, sirtuin activity falls and DNA repair slows, resulting in cellular aging (the accumulation of senescent cells) and chronic inflammation (“inflammaging”). Moreover, when inflammation occurs, an enzyme called CD38 consumes NAD even faster, creating a vicious cycle of “NAD decline → inflammation → further NAD decline” (summarized in a 2025 review by Nadis Academy). This is why interest in NAD supplementation has recently grown: external skincare alone cannot easily address these internal cellular energy and repair issues.

Management Method 1. Oral NMN Supplement — The Strongest Current Evidence

NMN (nicotinamide mononucleotide) is the immediate precursor of NAD, meaning it is the material that is converted into NAD in the body. Among the three management methods, it has the most clinical evidence in humans.

• In a randomized, double-blind trial in healthy older men, taking NMN 250 mg/day for 6 to 12 weeks significantly increased blood NAD and its metabolites, and some indicators of walking speed and grip strength showed improvement trends (Igarashi et al., 2022, npj Aging).
• In a human comparative study published in Nature Metabolism in 2025, taking NMN and NR (another precursor) for 14 days approximately doubled blood NAD, whereas ordinary nicotinamide did not produce the same effect (Christen et al., 2025).
• In terms of safety, a trial in healthy adults found no serious adverse events when NMN 1,250 mg/day was administered for 4 weeks (2022, randomized, placebo-controlled study).

That said, there are limitations that should be stated honestly. Large-scale clinical trials directly measuring skin improvement from NMN are still lacking, and current evidence combines the fact that it raises blood NAD with inference through the sirtuin and PARP mechanisms above. In addition, a meta-analysis combining 8 randomized controlled trials in healthy adults reported that improvements in metabolic markers such as blood glucose and lipids were not statistically clear (2024). In other words, NMN is a “validated tool for steadily replenishing NAD,” but the degree of perceived effect varies widely by individual.

Management Method 2. NAD Intravenous Injection — The Gap Between Popularity and Evidence

NAD intravenous injection became popular mainly through wellness clinics as a concept of directly delivering NAD into the bloodstream to replenish it quickly. Intuitively, it seems the most powerful, but recent human study results show that it is not as simple as expected.

The NAD molecule is large and has difficulty entering cells directly. In one human comparative study, NAD intravenous injection increased blood NAD by only about 2% 24 hours after administration, whereas NR intravenous injection increased it by about 20% in just 3 hours (2026, retrospective pilot study). In the NAD injection group, changes suggesting an inflammatory response, such as increases in white blood cells and neutrophils, were also observed.

In terms of experience, NAD intravenous injections often cause discomfort such as burning, nausea, and chest tightness when infused quickly, so they must be administered slowly (usually over tens of minutes to hours). The U.S. FDA has warned about contamination and quality risks in some compounded NAD injections. A 2020 systematic review concluded that randomized clinical trials of NAD injection therapy are few and that the evidence is “promising but still at an exploratory stage.”

In summary, NAD intravenous injection may be considered when rapid replenishment is desired or when oral absorption is difficult, but the common belief that “intravenous means unquestionably more effective” is not supported by current evidence. For aesthetic skin care and anti-aging purposes, it is advisable to receive sufficient guidance on expected effects, discomfort during infusion, and the evidence relative to cost before deciding.

Management Method 3. Lifestyle Habits — The Most Underrated NAD Strategy

Before supplements or injections, there are lifestyle habits that help reduce NAD consumption and support its production. Regular aerobic exercise stimulates NAD synthesis pathways, and adequate sleep and fasting (including intermittent fasting) are reported to help reduce NAD consumption. Above all, sun protection reduces the DNA damage that PARP must repair, making it the most cost-effective “NAD-saving” method.

Diore Clinical Principles

In our clinic, we guide NAD management not as “one procedure that ends the process,” but as something that is built up in order of evidence strength. First, we check the foundation such as sun protection, sleep, and exercise; then we add the oral precursors with the strongest evidence (NMN/NR); and only when rapid replenishment is needed or oral use is difficult do we present intravenous injection as an option after fully explaining its expectations and limitations. Since NAD management is an area where individual responses vary greatly, our principle is to provide guidance based on the current evidence without exaggeration.

Frequently Asked Questions (Q&A)

Q1. How much NMN supplement should I take per day to raise NAD?

In human trials, blood NAD increased significantly when 250 mg/day was taken for 6 to 12 weeks, and reports show that up to 1,250 mg/day was used safely for 4 weeks. There is still insufficient evidence that higher doses proportionally increase effectiveness, so consistency is generally more important than short-term high doses. Please consult a medical professional about any underlying conditions or medications before taking it.

Q2. Is NAD intravenous injection faster and better than taking NMN?

Contrary to intuition, in human studies NAD intravenous injection showed only a limited increase in blood NAD even after administration (about 2% after 24 hours), whereas precursor (NR) intravenous injection increased it by about 20% in just 3 hours. This is because the NAD molecule has difficulty entering cells directly. It is hard to say that intravenous administration is always superior.

Q3. Will NAD injections improve wrinkles or skin elasticity?

Mechanistically, it is clear that NAD is involved in collagen protection and DNA repair through sirtuins and PARP, but clinical skin studies directly proving that NAD injections improve wrinkles or elasticity are currently very limited. If your goal is cosmetic improvement, it is better to distinguish between mechanistic expectations and actual evidence.

Q4. Which is better, NMN or NR?

Both ingredients were shown in a comparative human study to raise blood NAD about twofold after 14 days of use, so their efficiency in increasing NAD is reported to be similar (Christen et al., 2025). In intravenous use, NR was shown to raise NAD more quickly. Rather than one being absolutely superior, the choice depends on the form of absorption and individual response.

Q5. Is it normal to feel nauseous or tight in the chest during NAD intravenous injection?

When infused quickly, burning, nausea, and chest pressure are commonly reported, which is why slow infusion is standard. However, if symptoms are severe or persist, you should inform the medical staff immediately.

Conclusion

NAD is a key coenzyme that connects aging and skin at the cellular level, and it is a definite fact that it decreases with age. However, what should be used to replenish it should be judged by the strength of the evidence, not by marketing. So far, lifestyle habits and oral precursors (NMN/NR) are the most validated foundation, and intravenous injection should be chosen only after receiving accurate guidance about expectations and limitations. At Diore Clinic, we assess each person’s skin condition and lifestyle together and design the management sequence accordingly.

ℹ️ This content is intended to provide general medical information and does not replace individual medical care. The indications and precautions for taking supplements such as NMN or receiving intravenous injections may vary depending on each person’s health status, and accurate diagnosis and consultation should be conducted with a medical professional specializing in skin and aesthetic treatments.