Research dossier
Clinical research on NAD+ Precursor (NR)
8 trials reviewed across 6 indications.
Strongest evidence
Raising NAD+ levels
Mechanism
NR is a NAD+ precursor that enters the salvage pathway via NR kinases (NRK1/2), bypassing some rate-limiting steps. Oral NR raises blood NAD+ and the NAD+ metabolome dose-dependently within hours and on chronic dosing.
This is the one thing NR clearly does: it raises blood NAD+, reproducibly and dose-dependently, across multiple independent trials (Trammell 2016, Martens 2018 ~60%, Wang 2022 ~doubled). Target engagement is not in question. What's in question is whether moving that biomarker does anything clinically useful — and so far, in rigorous trials, it largely hasn't.
The NAD+ rise is real in young and old. But a higher blood NAD+ reading is target engagement, not a health outcome. The case for needing supplemental NAD+ is mechanistic (NAD+ declines with age in animals), not outcome-proven in humans.
Trials cited
First-in-human NR pharmacokinetics
positive · RCT
Trammell et al., 2016, Nature Communicationsn=12Industry-fundedThe foundational human NR trial. Single oral doses of 100, 300, and 1,000 mg produced dose-dependent increases in the blood NAD+ metabolome in healthy adults, establishing that oral NR is bioavailable and raises NAD+ in people. This is the most reproducible NR finding.
n=12, single dose, pharmacokinetic study — not an efficacy trial. Funded by ChromaDex (maker of Niagen); several authors held ChromaDex stock or employment. Proves target engagement (NAD+ goes up), not clinical benefit.
Chronic NR raises NAD+ in middle-aged/older adults
mixed · RCT
Martens et al., 2018, Nature Communicationsn=306 weeks of 1,000 mg/day NR was well tolerated and raised whole-blood NAD+ by ~60%. Blood pressure and aortic stiffness only trended downward (and only in the subgroup with elevated baseline BP) without reaching significance on the cardiovascular endpoints. NAD+ went up; the hard cardiovascular markers did not clearly move.
n=30, 6 weeks. The BP and arterial-stiffness signals were secondary, non-significant, and subgroup-driven — the authors framed them as hypothesis-generating for future trials, not as a demonstrated effect.
NR and the aged human muscle NAD+ metabolome
mixed · RCT
Elhassan et al., 2019, Cell Reportsn=1221 days of 1,000 mg/day NR raised the NAD+ metabolome in aged skeletal muscle and lowered circulating inflammatory cytokines, with an anti-inflammatory transcriptomic signature. But it did not improve mitochondrial bioenergetics — in fact muscle energy-metabolism and mitochondrial gene pathways were downregulated.
n=12, 21 days. NAD+ and an anti-inflammatory signal rose, but the functional mitochondrial improvement that would justify the 'cellular energy' claim did not appear. Molecular signals, not functional outcomes.
NR metabolic phenotyping in overweight/obese adults
mixed · RCT
Remie et al., 2020, American Journal of Clinical Nutritionn=13Deep metabolic phenotyping with clamps, MRS, and muscle biopsies. NR raised muscle NAD+ synthesis markers but did NOT improve insulin sensitivity or mitochondrial function. There was a shift in body composition (fat mass down, fat-free mass and sleeping metabolic rate up), but the core metabolic endpoints were unchanged.
n=13, 6 weeks. The body-composition shift is an interesting secondary signal in a tiny sample, not a confirmed outcome — the pre-specified insulin-sensitivity and mitochondrial endpoints were null.
NR safety in heart failure with reduced ejection fraction
mixed · RCT
Wang et al. (Tian/O'Brien groups), 2022, JACC: Basic to Translational Sciencen=30A safety/mechanism trial in HFrEF patients. NR at up to 2,000 mg/day was safe, well tolerated, and roughly doubled whole-blood NAD+. Exploratory signals showed increased PBMC mitochondrial respiration and reduced pro-inflammatory (NLRP3-related) cytokine expression. No clinical cardiac-outcome endpoint was tested.
n=30, designed primarily for safety and mechanism, not clinical efficacy. The respiration and cytokine findings are exploratory in peripheral immune cells — promising mechanistically, but not evidence that NR improves heart failure outcomes.
Blood pressure & cardiovascular markers
Mechanism
Proposed improvements in endothelial function and arterial compliance via restored NAD+ and sirtuin activity. Heart-failure interest centers on NAD+ supporting cardiac and immune-cell mitochondrial respiration.
Martens 2018 saw only non-significant downward trends in blood pressure and aortic stiffness, confined to a high-baseline-BP subgroup — explicitly framed as hypothesis-generating. The HFrEF trial (Wang 2022) was a safety/mechanism study showing NR is safe and raises NAD+ in heart-failure patients, with exploratory anti-inflammatory and respiration signals in immune cells — but no clinical cardiac outcome was measured.
No trial has shown NR lowers blood pressure significantly or improves a hard cardiovascular outcome. The heart-failure work is early-stage and mechanistic. Treat cardiovascular benefit as unproven.
Chronic NR raises NAD+ in middle-aged/older adults
mixed · RCT
Martens et al., 2018, Nature Communicationsn=306 weeks of 1,000 mg/day NR was well tolerated and raised whole-blood NAD+ by ~60%. Blood pressure and aortic stiffness only trended downward (and only in the subgroup with elevated baseline BP) without reaching significance on the cardiovascular endpoints. NAD+ went up; the hard cardiovascular markers did not clearly move.
n=30, 6 weeks. The BP and arterial-stiffness signals were secondary, non-significant, and subgroup-driven — the authors framed them as hypothesis-generating for future trials, not as a demonstrated effect.
NR safety in heart failure with reduced ejection fraction
mixed · RCT
Wang et al. (Tian/O'Brien groups), 2022, JACC: Basic to Translational Sciencen=30A safety/mechanism trial in HFrEF patients. NR at up to 2,000 mg/day was safe, well tolerated, and roughly doubled whole-blood NAD+. Exploratory signals showed increased PBMC mitochondrial respiration and reduced pro-inflammatory (NLRP3-related) cytokine expression. No clinical cardiac-outcome endpoint was tested.
n=30, designed primarily for safety and mechanism, not clinical efficacy. The respiration and cytokine findings are exploratory in peripheral immune cells — promising mechanistically, but not evidence that NR improves heart failure outcomes.
Insulin sensitivity & metabolic health
Mechanism
NAD+ is a substrate for sirtuins, which regulate glucose and lipid metabolism. Rodent NR studies suggested improved insulin sensitivity and mitochondrial function — the hypothesis carried into human trials.
The metabolic claim has been directly tested and failed. Dollerup 2018 (2,000 mg/day, 12 weeks, insulin-resistant obese men) found no effect on insulin sensitivity, mitochondrial function, or metabolic flexibility. Remie 2020 (clamp + biopsies) also found no insulin-sensitivity or mitochondrial improvement. Two well-designed RCTs in the target population: null.
Tested in exactly the metabolically impaired population where benefit was expected, at a high dose, and it did not work. NR is not a metabolic therapy on current human evidence.
NR in obese insulin-resistant men (null)
Null · RCT
Dollerup et al., 2018, American Journal of Clinical Nutritionn=40A rigorous 12-week RCT at the high 2,000 mg/day dose in exactly the population (insulin-resistant obese men) where a metabolic benefit was expected. Result: no effect on insulin sensitivity, muscle mitochondrial function, or metabolic flexibility. A clean null on the headline metabolic claim.
One of the most important NR trials precisely because it is well-designed, adequately dosed, and negative on the endpoints NR is marketed to improve. The 'NR fixes metabolism' story does not survive this trial.
NR metabolic phenotyping in overweight/obese adults
mixed · RCT
Remie et al., 2020, American Journal of Clinical Nutritionn=13Deep metabolic phenotyping with clamps, MRS, and muscle biopsies. NR raised muscle NAD+ synthesis markers but did NOT improve insulin sensitivity or mitochondrial function. There was a shift in body composition (fat mass down, fat-free mass and sleeping metabolic rate up), but the core metabolic endpoints were unchanged.
n=13, 6 weeks. The body-composition shift is an interesting secondary signal in a tiny sample, not a confirmed outcome — the pre-specified insulin-sensitivity and mitochondrial endpoints were null.
Muscle, mitochondria & 'cellular energy'
Mechanism
NAD+ depletion is implicated in age-related mitochondrial dysfunction, so restoring NAD+ was hypothesized to improve muscle bioenergetics. Anti-inflammatory effects via reduced cytokine signaling are a secondary proposed route.
Elhassan 2019 raised muscle NAD+ in aged men and produced an anti-inflammatory signature — but did NOT improve mitochondrial bioenergetics (energy-metabolism gene pathways were actually downregulated). Dollerup and Remie also found no mitochondrial-function improvement. The 'NR powers your mitochondria' claim has molecular signals but no functional confirmation.
Anti-inflammatory and NAD+-metabolome effects in aged muscle are interesting biology, but no trial has shown improved muscle function, strength, or mitochondrial performance. Not an energy or muscle supplement on current evidence.
NR and the aged human muscle NAD+ metabolome
mixed · RCT
Elhassan et al., 2019, Cell Reportsn=1221 days of 1,000 mg/day NR raised the NAD+ metabolome in aged skeletal muscle and lowered circulating inflammatory cytokines, with an anti-inflammatory transcriptomic signature. But it did not improve mitochondrial bioenergetics — in fact muscle energy-metabolism and mitochondrial gene pathways were downregulated.
n=12, 21 days. NAD+ and an anti-inflammatory signal rose, but the functional mitochondrial improvement that would justify the 'cellular energy' claim did not appear. Molecular signals, not functional outcomes.
NR in obese insulin-resistant men (null)
Null · RCT
Dollerup et al., 2018, American Journal of Clinical Nutritionn=40A rigorous 12-week RCT at the high 2,000 mg/day dose in exactly the population (insulin-resistant obese men) where a metabolic benefit was expected. Result: no effect on insulin sensitivity, muscle mitochondrial function, or metabolic flexibility. A clean null on the headline metabolic claim.
One of the most important NR trials precisely because it is well-designed, adequately dosed, and negative on the endpoints NR is marketed to improve. The 'NR fixes metabolism' story does not survive this trial.
NR metabolic phenotyping in overweight/obese adults
mixed · RCT
Remie et al., 2020, American Journal of Clinical Nutritionn=13Deep metabolic phenotyping with clamps, MRS, and muscle biopsies. NR raised muscle NAD+ synthesis markers but did NOT improve insulin sensitivity or mitochondrial function. There was a shift in body composition (fat mass down, fat-free mass and sleeping metabolic rate up), but the core metabolic endpoints were unchanged.
n=13, 6 weeks. The body-composition shift is an interesting secondary signal in a tiny sample, not a confirmed outcome — the pre-specified insulin-sensitivity and mitochondrial endpoints were null.
Cognition
Mechanism
NAD+ supports neuronal energy metabolism and DNA repair; cerebral-blood-flow changes were proposed as a route to cognitive benefit. Largely mechanistic.
The one cognition RCT (Orr 2024, older adults with mild cognitive impairment) was null — NR raised NAD+ and was safe, but cognition did not separate from placebo. A cerebral-blood-flow change was noted without translating into cognitive performance. There is no positive human cognition trial for NR.
Small pilot, but the result is null. Do not use NR for cognition on current evidence.
NR for mild cognitive impairment (null)
Null · RCT
Orr et al., 2024, GeroScience (epub 2023)n=42A placebo-controlled randomized pilot (52 randomized, 42 completed: 22 NR, 20 placebo) in older adults with mild cognitive impairment. NR raised blood NAD+ and was safe, but it did not produce a meaningful cognitive improvement — the cognitive endpoints did not separate from placebo. A cerebral-blood-flow change was seen without a cognitive benefit.
Pilot/feasibility design, 10 weeks, primarily powered for safety. NAD+ rose as expected; cognition did not improve. There is no positive human cognition trial to set against this null.
Healthy aging & 'longevity'
Mechanism
NAD+ declines with age in animal tissues, and NAD+ precursors rescue some age-related declines in rodents via sirtuin and PARP pathways. This is the basis of the longevity marketing.
No human RCT has shown NR extends lifespan, healthspan, or any hard outcome. Notably, NR FAILED to extend lifespan in well-controlled mouse studies despite raising NAD+ — so even the animal longevity case is weaker than the marketing implies. And a 2022 preclinical study found NR-enriched diets associated with increased breast-cancer metastasis in mice, a measured reason for caution rather than enthusiasm.
Anti-aging benefit is unproven in humans and equivocal even in mice. Anyone buying NR for longevity is paying for a mechanism, not outcome evidence — and should weigh the preclinical cancer signal if they have a cancer history.
First-in-human NR pharmacokinetics
positive · RCT
Trammell et al., 2016, Nature Communicationsn=12Industry-fundedThe foundational human NR trial. Single oral doses of 100, 300, and 1,000 mg produced dose-dependent increases in the blood NAD+ metabolome in healthy adults, establishing that oral NR is bioavailable and raises NAD+ in people. This is the most reproducible NR finding.
n=12, single dose, pharmacokinetic study — not an efficacy trial. Funded by ChromaDex (maker of Niagen); several authors held ChromaDex stock or employment. Proves target engagement (NAD+ goes up), not clinical benefit.
NR uptake and breast-cancer metastasis (preclinical safety signal)
negative · Observational
Goun et al., 2022, Biosensors and BioelectronicsUsing a bioluminescent probe to track NR uptake in vivo, researchers found triple-negative breast cancer tumors took up far more NR than less aggressive lines, and NR-enriched diets were associated with increased cancer prevalence and brain metastasis in the mouse model. A measured safety signal: NAD+ fuels proliferation and DNA repair, which aggressive tumors can exploit.
Preclinical mouse data — not a human finding, and not proof that NR causes or worsens cancer in people. But it is a biologically plausible caution: anyone with active or recent cancer should avoid NR without oncology clearance.
4 forms of NAD+ Precursor (NR) compared
Niagen® (NR chloride)
Nicotinamide riboside (NR)
Well absorbed; raises blood NAD+ dose-dependently
Best forNAD+ precursor — studied for metabolism, cardiovascular markers, muscle, cognition (mostly null on outcomes)The branded, patented form (ChromaDex's Niagen, nicotinamide riboside chloride) is what almost every human trial used. The NAD+-raising effect is well established; the clinical-outcome evidence is not. Most positive-leaning trials are ChromaDex-funded — read the 'positive RCT count' as smaller than it looks.
Nicotinamide mononucleotide (NMN)
Raises blood NAD+ in humans; oral uptake mechanism debated
Best forThe other heavily-marketed NAD+ precursorNMN is one step further down the NAD+ pathway than NR. The two have comparable surrogate-endpoint evidence (both reliably raise NAD+; neither has shown lifespan extension in humans). No head-to-head RCT favors one on a clinical endpoint. NMN dominates the marketing (Sinclair/podcast hype); NR has the longer, more pharmacologically characterized trial history. See our NMN dossier for detail.
Niacinamide (nicotinamide)
Well absorbed
Best forThe cheap, classic NAD+ precursor / B3 vitamerNicotinamide is the simplest, cheapest NAD+ precursor and corrects niacin deficiency. It raises NAD+ too — the premium pricing of NR and NMN is sold on the claim of superior NAD+ delivery and fewer downsides, but the human outcome data don't establish that NR/NMN beat plain nicotinamide on health endpoints. See our niacin dossier.
Nicotinic acid (niacin)
Well absorbed
Best forLipid effects and pellagra repletion — a different pharmacologyAlso a B3 vitamer and NAD+ precursor, but with distinct pharmacology (flushing, lipid effects) and a failed cardiovascular-outcome history at high dose. Not interchangeable with NR for the NAD+/longevity use case. See our niacin dossier.
Are you deficient? Symptoms, risk groups, lab tests
NR is not an essential nutrient and has no RDA, EAR, or upper limit. The body makes NAD+ from several precursors (tryptophan, nicotinic acid, nicotinamide, and NR). Blood and tissue NAD+ have been reported to decline with age in animals and some human studies, but there is no validated clinical 'NR deficiency' or 'NAD+ deficiency' diagnosis. Frank niacin (B3) deficiency causes pellagra, which is treated with niacin/nicotinamide, not NR.
Common symptoms
- No defined NR-deficiency syndrome in humans
- NAD+ decline with age is a research concept, not a diagnosable condition
- Frank B3 deficiency (pellagra) is a separate, niacin-treated disorder
Who is at risk
Older adults (60+)
NAD+ and salvage-pathway capacity decline with age in animal tissue and some human data. Whether topping NAD+ back up with NR produces meaningful benefit is the open research question — the rigorous trials so far have been largely null on function.
Adults with metabolic disease
Altered NAD+ metabolism is associated with obesity and insulin resistance — but the best-designed trial in insulin-resistant obese men (Dollerup 2018) found no metabolic benefit from NR.
Lab markers
Whole-blood NAD+ / NAD+ metabolome
Not a routine clinical test. NR reliably raises it, so it works as a compliance / target-engagement biomarker — but a higher NAD+ reading is not itself evidence of clinical benefit, which is the central honesty point for this entire category.
Side effects and drug interactions
Side effects
Gastrointestinal upset (nausea, bloating, indigestion)
Uncommon · More common at 1,000 mg/day and above
The most common NR complaint across trials. Usually mild and dose-related; more likely at gram-level doses and on an empty stomach.
Flushing, fatigue, or headache
Rare
Reported infrequently. NR flushing is far less common than nicotinic-acid flushing. When these occur they are usually mild and transient.
Theoretical concern: NAD+ elevation in established cancer
Rare
NAD+ supports cell proliferation and PARP-mediated DNA repair. A 2022 preclinical mouse study linked NR-enriched diet to increased breast-cancer metastasis. Not demonstrated in supplemented humans, but a biologically plausible reason for anyone with active or recent cancer to avoid NR without oncology clearance.
Product quality and labeling accuracy
Uncommon
Independent testing has found NAD-precursor products that under-deliver the labeled amount. Buy from manufacturers that publish third-party purity testing; the branded Niagen form is the one actually used in trials.
Drug interactions
Other
Chemotherapy / cytotoxic cancer therapyPARP inhibitorsNAD+ is required for PARP-mediated DNA repair — precisely the pathway some oncology drugs are designed to block. Theoretical concern that boosting NAD+ could oppose PARP-inhibitor mechanism or support tumor-cell proliferation, with supporting preclinical signal.
Anyone in active cancer treatment or with recent cancer history should not supplement NR without explicit oncology clearance.
Additive effect
AntihypertensivesNR trended toward lowering blood pressure in a high-baseline-BP subgroup (non-significant). Any additive effect is likely small but worth noting when stacking with BP medication.
The effect is unproven and probably minor, but monitor if combining with blood-pressure medication.
Other
ImmunosuppressantsNAD+ modulates immune-cell metabolism via sirtuin and CD38 pathways; NR reduced inflammatory cytokine signaling in trial subgroups. Interaction with immunomodulatory therapy is plausible but uncharacterized.
Patients on systemic immunosuppression should consult their prescriber before adding NR.
Other critical caveats
- NR's one well-proven effect is raising blood NAD+. That is target engagement, not a health outcome. The rigorous human trials that tested whether the NAD+ rise improves anything — insulin sensitivity (Dollerup 2018), mitochondrial function (Remie 2020, Elhassan 2019), cognition (Orr 2024) — were largely null. The honest summary: it moves a biomarker, it has not yet shown it makes humans healthier.
- The evidence base is heavily industry-funded. Many NR trials are funded by ChromaDex (maker of Niagen) or use ChromaDex-supplied material. The most reproducible result (NAD+ goes up) is genuine, but treat the broader 'positive trial' framing with skepticism — independent, outcome-focused replication is limited.
- No human RCT has shown NR extends lifespan or any hard outcome. And unlike the rodent story for some precursors, NR failed to extend lifespan even in well-controlled mouse studies despite raising NAD+. The longevity case is weaker than the marketing implies, in mice and in humans.
- Preclinical cancer safety signal. A 2022 mouse study linked NR-enriched diet to increased breast-cancer (especially triple-negative) growth and brain metastasis, consistent with NAD+ fueling proliferation and DNA repair. This is animal data, not proof of human harm — but anyone with active or recent cancer should avoid NR without oncology clearance.
- NR vs NMN vs niacinamide: all raise NAD+, none has shown a clinical-outcome advantage in humans, and plain nicotinamide is far cheaper. The premium pricing of NR (and NMN) is sold on superior NAD+ delivery, not on superior health outcomes — because the outcome data to justify that premium don't exist yet.
Frequently asked
Does nicotinamide riboside actually do anything?
It reliably raises your blood NAD+ — that part is well proven and reproducible. The problem is what comes next: the careful human trials that tested whether the NAD+ rise improves insulin sensitivity, mitochondrial function, blood pressure, or cognition came back largely null. So the honest answer is: NR moves a biomarker, but it has not yet been shown to make humans measurably healthier. You're buying a mechanism, not a proven outcome.NR vs NMN — which is better?
Nobody has shown either is better on a clinical endpoint — there's no head-to-head outcome trial. Both reliably raise blood NAD+. NR (Niagen) has the longer, more pharmacologically characterized trial record; NMN has the louder marketing (Sinclair, podcasts). The clinical evidence doesn't favor either, and both share the same core problem: the NAD+ rise hasn't translated into proven health benefits in rigorous trials. If you're set on trying one, price and third-party testing matter more than the NR-vs-NMN debate.Will NR help me live longer or age slower?
There's no human evidence for that. No RCT has shown NR extends lifespan or healthspan. And the animal case is shakier than you'd think — NR failed to extend lifespan even in controlled mouse studies despite raising NAD+. There's also a 2022 preclinical study linking NR to worse breast-cancer metastasis in mice. For longevity specifically, you're paying for a hypothesis.Is NR safe?
Short-term human safety (up to 12 weeks, up to 2,000 mg/day) looks good — side-effect rates similar to placebo, with mild GI upset the most common complaint. Long-term safety isn't characterized. The specific caution worth taking seriously: a 2022 mouse study tied NR to increased breast-cancer metastasis, and NAD+ supports DNA-repair pathways some cancer drugs target. Anyone with active or recent cancer should clear NR with oncology first. Pregnancy and breastfeeding have no safety data.How much NR should I take?
Human trials used 100–2,000 mg/day. 1,000 mg/day reliably raises blood NAD+ (Martens 2018, ~60%); 300 mg is a common consumer dose. But here's the catch worth internalizing: higher doses raise the NAD+ biomarker more without any evidence they produce more clinical benefit — the well-designed trials at 2,000 mg/day (Dollerup) were still null on the endpoints that matter. More NAD+ on a blood test does not mean more health.
References
- 01Trammell et al., 2016 — First-in-human NR pharmacokinetics (Nature Communications)
- 02Martens et al., 2018 — Chronic NR raises NAD+ in older adults (Nature Communications)
- 03Dollerup et al., 2018 — NR in obese insulin-resistant men, null metabolic RCT (Am J Clin Nutr)
- 04Remie et al., 2020 — NR metabolic phenotyping RCT (Am J Clin Nutr)
- 05Elhassan et al., 2019 — NR and aged human muscle NAD+ metabolome (Cell Reports)
- 06Orr et al., 2024 — NR for mild cognitive impairment, null cognition RCT (GeroScience)
- 07Wang et al., 2022 — NR safety in heart failure (JACC: Basic to Translational Science)
- 08Goun et al., 2023 — NR uptake and breast-cancer metastasis, preclinical (Biosensors and Bioelectronics)
- 09Examine.com — Nicotinamide Riboside
Last reviewed2026-05-24