Nicotinamide riboside, an NAD+ precursor vitamin: does swallowing it raise NAD+? In human trials, blood NAD+ rose

Nicotinamide riboside, or NR, is an NAD+ precursor vitamin: a building block the body can turn into NAD+ (Conze 2019). In human trials, swallowing it raised blood NAD+. In an 8-week randomized, double-blind, placebo-controlled trial of overweight but otherwise healthy adults, 100, 300 and 1,000 mg of NR raised whole blood NAD+ by 22%, 51% and 142% within two weeks, and the rise held for the rest of the study (Conze 2019).

Here is how NR got from rodent studies to human trials, and what those trials measured.

How it was found

Interest in NR grew out of interest in NAD+. Researchers came to see NAD+ as a key co-substrate for enzymes involved in the benefits of regular calorie restriction on healthspan, and proposed NAD+ precursors as a way to improve physiological function with aging in humans (Martens 2018). In preclinical models, NAD+ was reported to decline with aging, but human data were sparse (Elhassan 2019).

In rodent studies, NR supplementation eased metabolic dysfunction (Elhassan 2019). The question for people was whether swallowing it would raise NAD+ at all.

In 2017, an open-label, non-randomized study of 8 healthy volunteers measured exactly that. They took 250 mg of NR on days 1 and 2, stepped up to 1,000 mg twice daily by days 7 and 8. Whole blood NAD+ rose 100% from baseline, and there were no adverse events (Airhart 2017).

In 2018, a randomized, double-blind, placebo-controlled crossover trial with two 6-week periods found that chronic NR was well tolerated and effectively stimulated NAD+ metabolism in healthy middle-aged and older adults (Martens 2018).

What the human trials later showed

The dose question came next. In the 8-week trial, each higher dose raised whole blood NAD+ further: 22% at 100 mg, 51% at 300 mg and 142% at 1,000 mg. The rise appeared within two weeks and held for the rest of the study, with no reports of flushing and no significant difference in adverse events versus placebo (Conze 2019).

In one 21-day randomized, double-blind, placebo-controlled crossover trial, 12 older men took 1 g of NR a day. NR raised the muscle NAD+ metabolome, which the authors take as evidence that oral NR is available to aged human muscle, and it lowered circulating inflammatory cytokines (Elhassan 2019).

At the high end, a four-week randomized, double-blind safety trial in 20 people with Parkinson’s disease gave 10 of them 1,500 mg twice daily. Blood NAD+ rose up to five-fold, with no moderate or severe adverse events (Berven 2023).

Study	Design	People	Dose / Duration	Result	Grade
Airhart 2017	Pilot (open-label, non-randomized)	8 healthy volunteers	250 mg stepped up to 1,000 mg twice daily / 9 days	Whole blood NAD+ rose 100%; no adverse events	B
Martens 2018	RCT (crossover)	Healthy middle-aged and older adults	Not reported / 2 × 6 weeks	Well tolerated; stimulated NAD+ metabolism	A
Conze 2019	RCT	Overweight but otherwise healthy adults	100, 300 or 1,000 mg / 8 weeks	Whole blood NAD+ rose 22%, 51% and 142% within 2 weeks, and held	A
Elhassan 2019	RCT (crossover)	12 older men	1 g a day / 21 days	Muscle NAD+ metabolome raised; circulating inflammatory cytokines lowered	A
Berven 2023	RCT	20 people with Parkinson’s disease (10 on NR)	1,500 mg twice daily / 4 weeks	Blood NAD+ rose up to five-fold; no moderate or severe adverse events	A
McDermott 2024	RCT	90 people with peripheral artery disease	Not reported (NR, with or without resveratrol) / 6 months	6-minute walk +17.6 meters versus placebo	A
Prokopidis 2025	Meta-analysis	Adults with a mean age of 60.9 to 83	NMN or NR versus placebo, several RCTs	Current evidence does not support NMN or NR for muscle mass and function	A

Beyond NAD+ levels, NR also has a walking result. In a 6-month randomized, double-blind trial of 90 people with peripheral artery disease, NR improved 6-minute walk distance by 17.6 meters versus placebo (+7.0 versus −10.6 meters), and adding resveratrol brought no further benefit (McDermott 2024).

The limit is muscle more broadly: a 2025 systematic review and meta-analysis of randomized trials concluded that current evidence does not support NMN or NR for preserving muscle mass and function in adults with a mean age over 60 (Prokopidis 2025).

Where it stands now

The human trials establish the NAD+ rise. NR raised whole blood NAD+ by 100% in an open-label study (Airhart 2017), by 22% to 142% depending on dose in an 8-week randomized trial (Conze 2019), and up to five-fold at 1,500 mg twice daily (Berven 2023), and it was well tolerated in the trials that reported safety. Whether that rise changes how energetic people feel day to day is something these trials did not measure.

Next step

The question most readers ask next is how a building block becomes NAD+ inside the body, and where NR sits in that pathway. The evidence page that maps that route, how NMN and NR become NAD+ in human trials, is the next one to read: https://healthspanpost.com/articles/how-do-nmn-and-nr-become-nad-in-human-trials-both-raised-blood-nad/

RULES CHECK

1 sourced: PASS — every research claim cites a paper in evidence.jsonl (Airhart 2017, Martens 2018, Conze 2019, Elhassan 2019, Berven 2023, McDermott 2024, Prokopidis 2025); years match evidence.jsonl 2 disclosure+sponsored: N/A — no product named, no affiliate link (discover day) 3 no testimonials: PASS 4 structure/function: PASS — no product on the page; disease populations named only as where trials ran 5 no persona: PASS 6 own channels: PASS 7 not AU / no creds: PASS 8 doubts: none Notes (reviewer): rewrote the title to be two-sided; cut uncited and inaccurate mechanism lines (“can’t swallow NAD+”, “rebuilt every time it is spent”); scoped Conze’s 22–142% to its one trial and population and dropped “per day” (not in the abstract); corrected Airhart (9-day uptitration, not single dose), Elhassan (muscle NAD+ metabolome, not muscle NAD+), Berven (10 of 20 on NR, Parkinson’s disease), McDermott (17.6 m is versus placebo) and Prokopidis (its conclusion covers NMN and NR; stated once, not three times); cited Martens 2018 for the calorie-restriction sentence lifted from its abstract; restored the real Berven and McDermott titles; added “What we don’t know yet”; US spelling.