Benefits
Documented blood NAD+ elevation
In placebo-controlled trials, NR raised blood NAD+ in a dose-dependent way: 22%, 51% and 142% at 100, 300 and 1,000 mg a day over 8 weeks, about 60% in blood immune cells at 1,000 mg a day in older adults, and about twofold at 1,000 mg a day over 2 weeks. This is a blood marker and does not by itself show a health benefit.
Mitochondrial function in human muscle
NR improves metabolic problems in rodents. In a 21-day crossover trial in 12 older men, 1 g a day raised the muscle NAD+ metabolome and lowered some circulating inflammatory markers, but it did not change muscle mitochondrial bioenergetics.
Cardiovascular biomarkers in older adults
In a 6-week crossover trial in 30 healthy adults aged 55 to 79, 1,000 mg a day was well tolerated. Exploratory analyses showed trends toward lower systolic blood pressure and aortic stiffness, mainly in people with above-normal baseline pressure, but neither change was significant after correction for multiple comparisons, and the subgroup analysis was exploratory. No cardiovascular outcome has been tested.
Cognitive tests unchanged in two trials in older adults
Two placebo-controlled pilot trials in older adults with mild cognitive impairment, 10 and 12 weeks long with up to 1 g a day, found that NR raised blood NAD+ at least twofold but did not improve cognitive test scores. Benefits seen in animal studies have not carried over to people so far.
Sirtuin and PARP enzyme support
NAD+ is the substrate for sirtuin enzymes, which are studied in aging research, and for PARP enzymes, which repair DNA. Raising NAD+ supplies these enzymes, but no human trial has shown that NR changes sirtuin activity, the pace of aging or lifespan.
Effects beyond NAD+ unproven in healthy adults
Raising blood NAD+ has not yet translated into clear health benefits in people: trials found no change in muscle mitochondrial function or cognitive scores, and blood-pressure effects were exploratory. The longevity case rests mainly on rodent research.
Mechanism of action
Nucleoside-transporter uptake and NRK phosphorylation
NR enters cells via nucleoside transporters and is phosphorylated by NR kinases (NRK1/2) to form NMN, which is then adenylylated to NAD+. This pathway bypasses the rate-limiting NAMPT step that limits nicotinamide (niacinamide) conversion. In mice, oral NR raised liver NAD+ more effectively than nicotinic acid or nicotinamide, and a human study suggests gut microbes convert part of an NR dose to nicotinic acid, which also feeds NAD+ production.
Sirtuin substrate supply
NAD+ is consumed by sirtuins, enzymes that remove chemical tags from proteins and so influence gene expression and protein activity; animal research links them to some effects of calorie restriction. Raising NAD+ supplies these enzymes, but no human trial cited here has measured sirtuin activity after NR.
PARP enzymes and DNA repair
NAD+ is also consumed by PARP enzymes, which signal DNA damage so that repair machinery can assemble. NAD+ levels have been reported to fall after DNA damage and with aging, mostly in animal research. Whether NR supplements change DNA repair in people has not been tested.
Clinical trials
Randomized, double-blind, three-arm crossover study: single oral doses of 100, 300 and 1,000 mg NR with 7-day washouts. ChromaDex supplied the NR and sponsored the study. (Trammell et al. 2016, Nat Commun)
12 healthy adults aged 30 to 55 (6 men, 6 women)
Each single dose raised the blood NAD+ metabolome in a dose-dependent way. Two people reported flushing at 300 mg and two reported feeling hot at 1,000 mg. Blood markers only; no health outcome was measured.
Randomized, double-blind, placebo-controlled crossover trial: NR 1,000 mg a day or placebo for 6 weeks each. (Martens et al. 2018, Nat Commun)
30 healthy adults aged 55 to 79
NR raised NAD+ in blood immune cells by about 60% versus placebo and was well tolerated. Systolic blood pressure and aortic stiffness showed only trends, larger in people with above-normal baseline pressure in an exploratory subgroup analysis; neither change was significant after correction for multiple comparisons.
Randomized, double-blind, placebo-controlled parallel trial: NR 100, 300 or 1,000 mg a day or placebo for 8 weeks. Funded by ChromaDex. (Conze et al. 2019, Sci Rep)
140 overweight but otherwise healthy adults (35 per group)
Whole-blood NAD+ rose 22%, 51% and 142% at the three doses within 2 weeks and stayed up. There were no reports of flushing, adverse events did not differ from placebo, and LDL cholesterol did not rise.
Randomized, open-label, placebo-controlled parallel study: NR 1 g, NMN 1 g, nicotinamide 0.5 g or placebo daily for 14 days. Eleven of the 12 authors are Nestle employees. (Christen et al. 2026, Nat Metab)
65 healthy adults analysed (mean age about 35)
NR and NMN each roughly doubled whole-blood NAD+ versus placebo; nicotinamide did not (P=0.461). All three were well tolerated.
Phase 2 randomized, double-blind, placebo-controlled pilot trial of NR 500 mg twice daily (1,000 mg a day) for 12 weeks in older adults with amnestic mild cognitive impairment. (Martens et al. 2026, Alzheimers Dement)
42 older adults with amnestic mild cognitive impairment completed (22 NR, 20 placebo)
Blood NAD+ doubled with NR, but cognitive function (the primary outcome), total cerebral blood flow and blood pressure did not improve. There were no serious adverse effects.