Does NAD+ Decline With Age, and Does Restoring It Help?

Probably yes, but the human evidence is thinner than the marketing suggests. Small cross-sectional studies have found lower NAD+ in the skin, brain, and muscle of older adults. The two brain imaging studies scanned only 17 and 16 people, and independent reviewers estimate from them a young-to-old difference of roughly 10 to 20 percent. Blood results conflict. Restoring it is a separate question. Oral precursors such as nicotinamide riboside (NR) and nicotinamide mononucleotide (NMN) reliably raise blood NAD+, yet randomized trials in people have so far shown few meaningful gains in muscle function, metabolism, or cognition. The striking benefits reported in aging mice have not been reproduced in humans.

What NAD+ does in your cells

NAD+ stands for nicotinamide adenine dinucleotide. It is a small molecule found in every living cell, built from vitamin B3 (niacin and its relatives) or from the amino acid tryptophan. You cannot live without it. Severe dietary deficiency of its building blocks causes pellagra, a disease of inflamed skin, digestive problems, and impaired mental function.

NAD+ has two very different jobs, and understanding both is the key to understanding why researchers think it matters for aging, and why raising it might not be a simple win.

Job one: carrying electrons to make energy

When your cells break down glucose and fat, they strip off electrons and hand them to NAD+, converting it to NADH. NADH then delivers those electrons to the mitochondria, the structures that produce most of your cellular energy in the form of ATP. Once it drops off its electrons, NADH becomes NAD+ again and the cycle repeats. Chemists call this shuttling redox (reduction and oxidation). In this role NAD+ is recycled, not used up.

The balance between the two forms, the NAD+ to NADH ratio, works as a readout of how a cell's energy metabolism is running. A lower ratio has been linked to less efficient mitochondrial function.

Job two: fuel for repair and signaling enzymes

The second job is different: here NAD+ is consumed. Three families of enzymes break NAD+ apart to do their work, which means the cell must constantly rebuild its supply.

• Sirtuins are enzymes that remove chemical tags from proteins, including the proteins that package DNA. They help regulate metabolism, stress responses, and mitochondrial function, and they cannot work without NAD+.
• PARPs (poly-ADP-ribose polymerases) detect breaks in DNA and flag them for repair. Each repair event uses NAD+, so heavy DNA damage can drain a cell's supply.
• CD38 is an enzyme found largely on immune cells that breaks down NAD+ and also degrades NMN, one of its precursors. In mice, CD38 levels and activity rise with age.

Because these enzymes compete for the same pool, a cell with more DNA damage or more inflammation may have less NAD+ left over for everything else. That competition is the core of the "NAD+ decline" theory of aging described in scientific reviews of the field.

How the body makes and recycles NAD+

Most NAD+ in adult tissues is not made from scratch. It is recycled through the salvage pathway: when sirtuins, PARPs, or CD38 consume NAD+, they release nicotinamide, and an enzyme called NAMPT converts that nicotinamide back toward NAD+. NAMPT is the rate-limiting step, the bottleneck, in this recycling loop in skeletal muscle. NR and NMN are intermediates that enter the same pathway a step or two closer to the finished product, which is why they are sold as "NAD+ precursors."

Does NAD+ really fall with age in humans?

You will often read that NAD+ levels drop by half by middle age. That specific claim does not hold up well when you look at where it comes from. The honest summary is that a decline has been observed in several human tissues, but in a small number of small studies, none of which followed the same people over time.

Skin

The most cited human study, published in 2012, measured NAD+ in samples of non-sun-exposed pelvic skin from 49 people ranging from newborns to age 77. NAD+ fell with age in both sexes. Among post-pubescent males the correlation with age was r = -0.706, and among post-pubescent females it was r = -0.537. (A correlation of -1 would be a perfect straight-line decline; 0 would be no relationship.) PARP activity rose with age in males when newborns were included, although that trend was no longer statistically significant among post-pubescent males alone. DNA damage markers rose with age in both sexes, which fits the idea that DNA repair consumes more NAD+ as we get older.

This is a real finding, but note its limits: one tissue, 49 people, a single time point per person, and a wide age range that included infants, whose very high levels steepen the apparent slope.

Brain

In 2015, a University of Minnesota team used high-field magnetic resonance spectroscopy, a scanner-based method that detects molecules without a biopsy, to measure NAD+ and NADH in the brains of 17 healthy volunteers aged 21 to 68. They reported that with increasing age NAD+ fell (correlation r = -0.75), total NAD fell, the NAD+ to NADH redox potential fell, and NADH rose. The paper did not report a percentage decline. A second scanner study, published in 2020, found an age-related decline in brain NAD+ in 16 people aged 26 to 78. A later critical review estimated from the published figures of these two studies that brain NAD+ differs between young and older adults by a modest 10 to 20 percent. That figure is the reviewers' estimate, not a number reported by either study.

Skeletal muscle

A 2022 study in Nature Aging compared muscle biopsies from young adults with those from older adults who were exercise trained, normally active, or physically impaired. NAD+ was one of the most prominently reduced metabolites in older muscle. The pattern was graded: impaired older adults had the lowest levels, while trained older adults had levels closer to those of young people. NAD+ abundance tracked with average daily step count and with measures of mitochondrial and muscle function.

That last detail matters. It suggests that at least part of what looks like an effect of age may be an effect of inactivity and declining health, which tend to come along with age but are not the same thing.

Blood

Blood is the easiest tissue to sample and the hardest to interpret. A 2019 study of about 30 healthy adults aged 20 to 87 found that plasma NAD+ and NADP+ were lower in older participants, while breakdown products such as nicotinamide and ADP-ribose were higher. The authors themselves flagged the small sample as a limitation. Other blood studies have reached different conclusions, and the critical review mentioned above describes blood findings as highly contradictory, ranging from no change to very large reductions. NAD+ does most of its work inside cells, so the small amount floating in plasma may say little about what is happening in your muscles or brain.

How strong is this evidence overall?

A 2021 systematic look at the question, pointedly titled "Age-dependent decline of NAD+: universal truth or confounded consensus?", concluded that evidence for a general decline is "very limited and often restricted to a single tissue or cell type." The authors noted that the human studies were all cross-sectional (comparing different young and old people rather than following individuals), that most were very small, and that different measurement methods give inconsistent numbers. Beyond skin, brain, and muscle, they found single studies of liver and spinal fluid. In the liver study, NAD+ in non-diseased liver tissue from 6 surgical patients over age 60 was about 65 to 70 percent of the level in 6 patients under 45, roughly 30 percent lower; all 12 were having surgery for liver cancer or bile duct stones. In the spinal fluid study of 70 people, total NAD (NAD+ and NADH measured together) averaged about 14 percent lower in those over 45 than in those 45 and under, a difference of borderline statistical significance (p = 0.05).

A 2025 review in Nature Metabolism reached a similar verdict: an age-related decline in humans "has been consistently observed only in a limited number of studies," and extrapolating from rodents "is not straightforward."

So the fair answer to "does NAD+ decline with age?" is: probably, in at least some tissues, by a modest amount, and how you live appears to influence it. It is not the steep, universal, clock-like drop that advertising implies.

Why levels might fall: the leading explanations

If NAD+ does fall, there are only two ways it can happen: the body makes less, or it uses more. Research points to both, though most of the mechanistic work is in mice.

More consumption: CD38 and chronic inflammation

In a 2016 mouse study from the Mayo Clinic, expression and activity of CD38 increased with age, and mice lacking CD38 were protected from age-related NAD+ decline and the mitochondrial dysfunction that went with it. A 2020 mouse study filled in a possible upstream cause. Senescent cells, which are worn-out cells that stop dividing and secrete inflammatory signals, accumulated in fat and liver with age. Their secretions pushed nearby immune cells called macrophages to multiply and produce CD38, which in turn lowered tissue NAD+.

If this chain holds in people, it reframes the problem. Low NAD+ would be partly a downstream consequence of chronic, low-grade inflammation rather than a simple shortage that can be topped up. These are animal findings; the same sequence has not been demonstrated in living humans.

More consumption: DNA damage and PARPs

The human skin study described above found that PARP activity climbed with age in males (a trend that depended on including newborns) and was inversely related to NAD+. Accumulating DNA damage could plausibly pull NAD+ away from other uses. This is an association in one human tissue, supported by cell and animal experiments.

Less production: a slower salvage pathway

In a study of 57 people, the amount of NAMPT (the bottleneck recycling enzyme) in skeletal muscle was lower with increasing age, and aerobic fitness, measured as peak oxygen uptake, was the best predictor of NAMPT levels. As discussed below, exercise training reversed this.

What happens when NAD+ is restored in animals

The excitement around NAD+ comes almost entirely from rodent studies, and those results are striking. Two examples are cited more than any others.

• NMN for 12 months in mice. In a 2016 study, normal mice given NMN in their drinking water for a year showed less age-associated weight gain, better energy metabolism, more physical activity, improved insulin sensitivity and blood lipids, and better eye function, without obvious toxicity.
• NR in old mice. A 2016 paper in Science reported that NR rejuvenated muscle stem cells in aged mice, delayed senescence of neural and pigment stem cells, and increased mouse lifespan.

Now the counterweight. The Interventions Testing Program is a long-running effort that tests candidate longevity compounds in genetically heterogeneous mice, a design intended to give sturdier answers than studies in a single inbred strain. When that program tested NR, it reported in 2021 that NR did not significantly increase lifespan in either sex at the dose tested, despite, in the authors' words, "some data suggesting that nicotinamide riboside would be effective."

Animal studies like these justify human trials. They do not substitute for them. Laboratory mice are often studied under conditions, such as high-fat diets, specific disease models, or a single inbred strain, that exaggerate a deficit and the benefit of fixing it. The 2025 Nature Metabolism review makes the same point: rodent results have not translated cleanly.

What human trials of NAD+ restoration have shown

Dozens of randomized controlled trials of NR and NMN have now been published. Almost all are small (most enrolled 12 to 90 participants) and short (3 weeks to 6 months). Two findings are consistent across them. First, oral precursors do raise NAD+ in blood. Second, that rise has rarely translated into changes a person would notice or a doctor would consider clinically important.

Do precursors actually raise NAD+ in people?

Yes, in blood, and this is the best-established fact in the field. The first human pharmacokinetic study of NR, published in 2016, found dose-dependent increases in the blood NAD+ metabolome after single doses of 100, 300, and 1,000 mg. In a 6-week crossover trial in 24 healthy adults aged 55 to 79, 1,000 mg of NR per day raised NAD+ in circulating immune cells by about 60 percent. Trials in people with mild cognitive impairment have reported twofold to 2.6-fold increases in blood NAD+, a long COVID trial using 2,000 mg per day reported 2.6-fold to 3.1-fold increases, and a Parkinson's disease safety trial using 3,000 mg per day reported up to a fivefold increase. NMN at 300, 600, or 900 mg per day raised blood NAD levels in an 80-person trial, with the highest levels at the two larger doses.

Tissue is a murkier story. In 12 older men given 1 g of NR daily for 21 days, muscle biopsies showed increases in NAD+-related metabolites, which indicates the supplement reached muscle, but mitochondrial energy production in that muscle did not change. In the NADPARK trial, brain NAD levels measured by MR spectroscopy rose on NR, though the authors described the response as "significant, but variable" from person to person.

Raising a number on a lab report is not the same as improving health. The trials below asked the question that matters.

Muscle strength and physical function

This is where mouse data set the highest expectations, and where human results have been most sobering.

• Healthy older adults, NR. In the 6-week, 24-person crossover trial, 1,000 mg per day had no effect on maximal exercise capacity or motor function.
• Older men, NMN. A Japanese trial gave 250 mg of NMN daily to healthy men aged 65 and older. Because of a supplement distribution error, only 20 of 42 participants completed the 12-week protocol as planned. The authors reported "nominally significant" improvements in gait speed and left-hand grip strength that, in their words, "should be validated in larger studies," and no effect on body composition.
• Middle-aged adults, NMN. In an 80-person, 60-day trial, six-minute walking distance improved more in all three NMN dose groups than with placebo. The analysis was per protocol, and several authors were employees of companies in the NMN business, so this result needs independent replication.
• Overweight adults 45 and older, NMN. Twenty-eight days of 1,000 mg twice daily produced no difference from placebo in muscle strength, muscle fatigability, aerobic capacity, or stair-climbing power.
• Amateur runners, NMN. In 48 runners training for 6 weeks, medium and high doses improved some measures of oxygen use at submaximal thresholds, but maximal oxygen uptake (VO2max) and peak power did not differ from placebo.
• Peripheral artery disease, NR. In the 90-person NICE trial, 6 months of NR improved six-minute walk distance by 17.6 meters relative to placebo. The authors called for a larger confirmatory trial. This is a specific disease population with impaired leg blood flow, not healthy aging.

A 2025 systematic review and meta-analysis pooled the randomized trials in adults with mean ages of about 61 to 83. It found no significant effect of NMN on skeletal muscle index, handgrip strength, gait speed, or chair-stand time, and concluded that "current evidence does not support NMN and NR supplementation for preserving muscle mass and function" in this age group.

Metabolism, blood sugar, and body composition

The most rigorous metabolic trial was done in Denmark: 40 sedentary men with obesity and insulin resistance, aged 40 to 70, received 2,000 mg of NR per day or placebo for 12 weeks. Using the gold-standard clamp technique to measure insulin sensitivity, the investigators found no improvement in insulin sensitivity, glucose production, or glucose disposal, and no change in resting energy expenditure, fat breakdown, or body composition.

Other trials have found scattered signals:

• In 13 overweight or obese adults, 6 weeks of NR at 1,000 mg per day increased fat-free mass as a share of body weight by about 1.3 percentage points and raised sleeping metabolic rate, but had no effect on insulin sensitivity, mitochondrial function, liver fat, heart function, blood pressure, or inflammatory markers.
• In 25 postmenopausal women with prediabetes and overweight or obesity, 10 weeks of NMN at 250 mg per day improved insulin-stimulated glucose uptake in muscle, measured by clamp, while placebo did not. This is the most encouraging metabolic result to date, in one specific group.
• In 30 overweight or obese adults aged 45 and older, 28 days of NMN at 1,000 mg twice daily lowered body weight by 1.9 kg, diastolic blood pressure by about 7 mmHg, and LDL cholesterol by about 19 mg/dL relative to placebo. Insulin sensitivity, liver fat, and abdominal fat did not change.
• In 20 pairs of identical twins who differed in body weight, 5 months of NR (up to 1,000 mg per day) increased the number of mitochondria in muscle and altered gut bacteria, yet, in the authors' words, "did not ameliorate adiposity or metabolic health."

A 2026 meta-analysis of 15 randomized NMN trials, with doses of 250 to 2,000 mg per day for 14 days to 24 weeks, found no significant effects on body weight, BMI, fasting glucose, HbA1c, lipid profiles, or systolic blood pressure. Diastolic blood pressure fell slightly. The authors concluded that "broad metabolic benefits were not evident." If you are weighing options for metabolic health, the evidence base behind proven medical weight loss treatments is of a different order of magnitude.

Blood pressure and blood vessels

In the 24-person NR trial in healthy older adults, systolic blood pressure was 3.9 mmHg lower on NR than placebo, and arterial stiffness trended lower, but neither result was statistically significant after correction for multiple comparisons. In an exploratory look at the 13 participants whose systolic pressure started at 120 to 139 mmHg, the difference was about 9 mmHg; the authors made no statistical claim for it and recommended a dedicated trial. A 2026 pilot trial by the same lead investigator in people with mild cognitive impairment found no improvement in blood pressure over 12 weeks.

Cognition and brain health

Given the brain imaging data on age-related decline, cognition is a natural target. Three placebo-controlled trials have now tested it directly, and none found a benefit on its primary cognitive outcome.

• Mild cognitive impairment, 2024. Twenty older adults took NR, escalated to 1 g per day, or placebo for 10 weeks. Blood NAD+ rose 2.6-fold. Scores on the Montreal Cognitive Assessment and other cognitive tests did not change.
• Amnestic mild cognitive impairment, 2026. Forty-two participants completed 12 weeks of NR or placebo. Blood NAD+ doubled. There were no improvements in cognitive function (the primary outcome), total cerebral blood flow, or blood pressure. Exploratory analyses hinted at regional blood flow increases in the hippocampus.
• Long COVID, 2025. Fifty-eight adults took NR at 2,000 mg per day or placebo in a 24-week trial. There were no significant between-group differences in cognition, fatigue, sleep, anxiety, or depression. Dropout was high, about half of the main NR group by 20 weeks. Within-group improvements seen in a post hoc analysis were not adjusted for multiple comparisons.

Parkinson's disease is the area with the most momentum. In the 30-person phase 1 NADPARK trial, newly diagnosed patients took 1,000 mg of NR or placebo for 30 days. Those whose brain NAD levels rose showed altered brain metabolism on PET imaging and mild clinical improvement. A follow-up safety trial found 3,000 mg per day well tolerated for 4 weeks in 20 patients, with a slight initial rise in homocysteine. The decisive test is the phase 3 NOPARK trial, which enrolled 410 people with early Parkinson's disease for 52 weeks of NR or placebo. According to its ClinicalTrials.gov record, the trial was completed in June 2025. As of September 2026, no results had been posted to the registry, and none could be located in the published literature.

Inflammation

One of the more reproducible secondary findings is a reduction in circulating inflammatory markers. NR lowered levels of several inflammatory cytokines in the 12-person study of older men, and in both blood and spinal fluid in NADPARK. A 2023 critical review of all 25 human NR studies then published agreed that NR "may play a role in the reduction of inflammatory states." Whether this translates into fewer diseases is unknown.

The overall verdict from independent reviewers

That same 2023 review, written by researchers who run NR trials themselves, concluded that oral NR "has displayed few clinically relevant effects, and there is an unfortunate tendency in the literature to exaggerate the importance and robustness of reported effects." The 2025 Nature Metabolism review likewise summarized that human clinical trials "have shown limited efficacy."

NAD+ itself by IV or injection: what is known

Everything above concerns oral precursors, because that is where the randomized trials are. NAD+ given directly by vein or under the skin has far less research behind it. The most detailed published human study is a 2019 pilot in 11 healthy men aged 30 to 55: eight received 750 mg of NAD+ intravenously over 6 hours and three received saline. Plasma NAD+ did not change for the first 2 hours, then rose to about 398 percent above baseline by the end of the infusion, with a large increase in NAD+ and its breakdown products in urine. No adverse events were recorded. The study was conducted at, and partly funded by an affiliate of, a clinic that sells NAD+ infusions, and it measured blood and urine chemistry only. It did not test whether anyone felt, functioned, or aged any differently.

Regulatory status. As of September 2026, NAD+ is not an FDA-approved drug for any condition. Injectable NAD+ comes either from compounding pharmacies or from peptide suppliers; neither route is FDA-reviewed. On the compounding side, the FDA's list of bulk substances nominated for compounding under section 503A, updated May 14, 2026, places nicotinamide adenine dinucleotide in Category 1, "bulk drug substances under evaluation," which means the agency has not yet made a final decision about it, and compounded drugs are not reviewed by the FDA for safety, effectiveness, or quality before they are dispensed. NR and NMN are sold as dietary supplements, which also do not go through FDA approval; in a citizen petition response dated September 29, 2025, the FDA concluded that NMN is not excluded from the definition of a dietary supplement, reversing the position it had taken in late 2022.

NAD+ is also sold by anonymous online sellers labeled "for research use only" for self-directed injection with no prescriber involved, and that route offers no way to know what is in the vial or what dose you are taking. A physician-provided route adds what self-directed use lacks: an independent laboratory test for identity and purity on each batch, a certificate of analysis the patient can see, reconstitution in the office, written dosing instructions, and medical follow-up. None of that makes the product FDA-approved or changes the state of the evidence. Rx2BFIT offers NAD+ by injection, not IV infusion, and does not use a compounding pharmacy. Its NAD+ comes from a supplier whose batches are tested by an independent laboratory for identity and purity, with a certificate of analysis on file, and is reconstituted in the office under Dr. Patel's supervision. It is not an FDA-approved product, and the limits of the human evidence are part of what Dr. Patel reviews with every patient before starting.

For a route-by-route breakdown, see the companion guide on NAD+ injections, IV therapy, and oral supplements. General background on how the therapy is delivered is on the NAD+ treatment page.

Safety, side effects, and the cancer question

Short-term safety in trials

Across published trials, NR and NMN have been well tolerated. The 2026 meta-analysis of NMN trials found no increase in overall adverse events, serious adverse events, withdrawals, or liver enzyme elevations at 250 to 2,000 mg per day for up to 24 weeks. In the Danish trial, 2,000 mg per day of NR for 12 weeks produced no serious adverse events attributed to NR and normal safety blood tests. Side effects reported with NR in the healthy older adult trial were mild and infrequent: nausea, flushing, leg cramps, and increased bruising.

Two caveats deserve emphasis. The longest of these trials ran about 6 months, and most enrolled a few dozen people, so they cannot detect rare harms or harms that take years to develop. And the authors of the 2026 meta-analysis specifically called for larger, longer trials to confirm long-term safety.

Why scientists raise cancer as a theoretical concern

Cancer cells are hungry for energy and divide rapidly, and both processes depend on NAD+. Researchers have long noted that NAD+ metabolism influences cancer as well as aging. That raises a reasonable question: could flooding the body with NAD+ precursors feed an existing, undetected cancer?

Two laboratory findings keep this question alive:

• A 2019 study in Nature Cell Biology, using cell cultures and mouse models, showed that higher NAD+ metabolism amplifies the inflammatory secretions of senescent cells, secretions that are known to promote tumor growth. The authors concluded that NAD+ augmentation for anti-aging purposes "should be administered with precision."
• A 2023 study in mice with triple-negative breast cancer found that NR supplementation significantly increased cancer prevalence and metastasis to the brain. The authors stressed the need to personalize use in certain patient populations.

On the other side of the ledger, there is a large human trial of a related compound. In the phase 3 ONTRAC trial, published in the New England Journal of Medicine, 386 people with a history of skin cancer took nicotinamide (a form of vitamin B3 and the most direct NAD+ salvage substrate) at 500 mg twice daily or placebo for 12 months. The rate of new non-melanoma skin cancers was 23 percent lower with nicotinamide, and adverse events did not differ between groups. The benefit disappeared after participants stopped taking it. Nicotinamide is not NR or NMN, and skin cancer is not all cancer, but this result shows that raising NAD+ availability does not automatically promote tumors in humans.

The bottom line: no human trial has shown that NAD+ precursors cause or accelerate cancer, and no human trial has been large or long enough to rule it out. If you have a current or past cancer diagnosis, this is a conversation to have with your oncologist before using any NAD+ product.

Other open questions

The 3,000 mg per day Parkinson's trial noted a slight early rise in homocysteine, an amino acid linked to cardiovascular risk when elevated, although the authors reported that the body's methyl donor pool remained intact. People who are pregnant or breastfeeding, children, and people with significant liver or kidney disease have essentially not been studied. High doses of the older vitamin B3 form nicotinic acid (niacin) can cause flushing, raised blood sugar, and liver damage. Flushing was also among the mild events reported with NR in one trial. That history is a reminder that B3 compounds are not automatically harmless at pharmacologic doses.

Seek urgent medical care if, after any injection or infusion, you develop trouble breathing, chest pain or pressure, swelling of the face or throat, fainting, a high fever, or spreading redness and pain at the injection site.

Lifestyle factors that raise NAD+

The intervention with the best human evidence for improving NAD+ biology is not a product.

Exercise

In the 57-person study mentioned earlier, 12 weeks of training increased muscle NAMPT, the bottleneck enzyme for NAD+ recycling. Aerobic training raised it by 12 percent in young adults (35 and under) and 28 percent in older adults (55 and over). Resistance training raised it by 25 percent in the young and 30 percent in the older group. The authors concluded that exercise training reverses the age-dependent decline in muscle NAMPT.

This dovetails with the Nature Aging biopsy study: trained older adults had muscle NAD+ levels close to those of young adults, and NAD+ abundance rose with daily step count. Both aerobic and resistance exercise also have what NAD+ supplements lack: recognized benefits for the outcomes people actually care about. The U.S. National Library of Medicine lists stronger muscles and bones, fewer falls in older adults, better blood sugar and insulin control, and a lower risk of heart disease among them. If exercise is not producing the changes you expect, the guide on why you might be working out but not losing fat covers the common reasons.

Adequate vitamin B3 in your diet

Your body builds NAD+ from niacin, nicotinamide, and tryptophan in food. The recommended daily intake of niacin is 16 mg for adult men and 14 mg for adult women, according to the U.S. National Library of Medicine. Good sources include poultry, fish, lean meats, peanuts, legumes, eggs, milk, rice, and enriched breads and cereals. Most people eating a varied diet meet this easily. There is no good evidence that eating more B3 than you need raises tissue NAD+ in a way that improves health; the point is simply that the raw materials are ordinary nutrients.

Reducing the drains on NAD+

The mechanistic research suggests that chronic inflammation and DNA damage increase NAD+ consumption. It follows, in theory, that the habits known to reduce both, such as not smoking, protecting skin from excessive sun, maintaining a healthy weight, sleeping enough, and limiting alcohol, should help preserve NAD+. To be clear about the evidence tier: these habits are well proven to improve health, but their specific effect on human tissue NAD+ levels has mostly not been measured directly. Calorie restriction has been tied to NAD+-dependent enzymes in laboratory research; comparable human tissue data are sparse.

Myths versus realities

Myth: NAD+ falls by half by age 50 in everyone

Reality: no longitudinal human study has tracked NAD+ in the same people over decades. Cross-sectional studies suggest modest declines in some tissues, an estimated 10 to 20 percent in brain based on two small imaging studies, and physically active older adults can have muscle levels similar to young adults.

Myth: if a supplement raises your blood NAD+, it is working

Reality: nearly every trial shows higher blood NAD+, and most of those same trials show no change in strength, insulin sensitivity, or cognition. Blood NAD+ is a marker of absorption, not of benefit.

Myth: the mouse studies prove it slows aging

Reality: individual labs reported impressive results in mice, including a lifespan increase with NR. A later lifespan study in genetically heterogeneous mice, the Interventions Testing Program, did not find a lifespan benefit from NR in either sex. No human study has tested lifespan or disease prevention.

Myth: NAD+ therapies are FDA approved

Reality: as of September 2026, NAD+ is not an FDA-approved drug. Injectable NAD+ comes either from compounding pharmacies or from peptide suppliers; neither route is FDA-reviewed, and the bulk substance is still under FDA evaluation for compounding. NR and NMN are dietary supplements that are not evaluated for effectiveness before sale.

Myth: it is natural, so there is no downside

Reality: short-term trials are reassuring, but none has run longer than about 6 months, and laboratory studies raise an unresolved question about feeding existing cancers. Unknown is not the same as safe.

Who might reasonably consider it, and who should be cautious

Given the state of the evidence, NAD+ restoration is best understood as experimental wellness therapy with a good short-term safety record and unproven benefits. Some adults decide that trade-off is acceptable, particularly if they have the basics of healthy aging in place and understand they are acting ahead of the evidence. Others reasonably decide to wait for larger trials.

Extra caution, and a specific conversation with the relevant specialist, is warranted if you:

• Have an active cancer or a history of cancer
• Are pregnant, trying to conceive, or breastfeeding, because these groups have not been studied
• Have significant liver or kidney disease
• Take multiple prescription medications, since interaction data are minimal
• Are considering it in place of, rather than alongside, a treatment with proven benefit for a diagnosed condition

Questions to ask your doctor

1. Which form are you recommending (oral NR, oral NMN, injected or IV NAD+), and what human evidence exists for that specific form and route?
2. What outcome are we trying to change, and how will we measure whether it is working, beyond a blood NAD+ level?
3. Where does the product come from, is each batch tested by an independent laboratory for identity and purity, can I see the certificate of analysis, and what is its current FDA status?
4. Given my personal and family history of cancer, does the theoretical cancer concern change your advice for me?
5. How long would you suggest I try it before we decide it is not doing anything?
6. Could any of my current medications or conditions make this a poor choice?
7. What would you prioritize first for my goals: exercise programming, sleep, nutrition, or treatment of a specific condition?

A prescriber who welcomes these questions and answers them with reference to actual studies, including the negative ones, is giving you what you need to make an informed choice.

This is general information, not medical advice. Whether a treatment is right for you is determined by a licensed provider after an evaluation.