Nicotinamide Riboside (NR)

Think of NAD+ as the petrol your cells burn. NR genuinely fills the tank back up, and that part is real and measurable. The trouble is that topping up a healthy car's tank doesn't make it go faster or last longer if the engine wasn't actually running on empty. So far, in most people, NR fills the tank but the car drives much the same, though in one group with badly furred-up fuel lines (peripheral artery disease) it did help them go a little further.

NR is a precursor that the body converts into NAD+, a coenzyme essential for converting nutrients into cellular energy and for powering enzymes such as sirtuins and PARPs involved in DNA repair and metabolic regulation. Taken orally, NR enters cells and is phosphorylated by nicotinamide riboside kinases (NRK1/NRK2) to nicotinamide mononucleotide (NMN), which is then converted to NAD+. Crucially this route bypasses NAMPT, the normally rate-limiting enzyme of the NAD+ salvage pathway, which is the proposed reason NR can raise NAD+ efficiently. The therapeutic hypothesis is that restoring the age-related decline in NAD+ will improve mitochondrial and metabolic function; in humans the NAD+ increase is real but the downstream functional benefit has, in most trials, not materialised.

Research contexts. Not proven uses, and not recommendations.

Unusually for a supplement, there is a substantial body of completed human RCTs, and that's exactly why the honest verdict is sobering. NR is reliably absorbed and consistently raises blood NAD+ (Trammell 2016 established the pharmacokinetics; Martens 2018 showed a marked, well-tolerated chronic elevation in healthy middle-aged and older adults). But the trials measuring actual health outcomes are mostly null or marginal: studies in overweight/obese and metabolically impaired people found no improvement in insulin sensitivity, body composition, mitochondrial function or hepatic fat, and a 2025 systematic review/meta-analysis (Prokopidis et al.) found NR/NMN did not preserve muscle mass or function in older adults. The notable exception is the NICE randomised trial in peripheral artery disease (2024), which met its primary endpoint with a modest but statistically significant gain in 6-minute walk distance. Safety-focused trials in Parkinson's disease (NR-SAFE, high-dose) confirmed tolerability without proving benefit, and a long-COVID RCT raised NAD+ but did not improve cognition, fatigue, sleep or mood. A 2023 critical review in Science Advances assessed 25 human studies and concluded NR has displayed few clinically relevant effects, with a tendency in the literature to exaggerate weak results. In short: the biomarker reliably moves, and apart from a walking benefit in PAD the patient generally doesn't.

• !Efficacy gap: NR reliably raises NAD+ but most human trials have failed to show clinical benefit, so broad anti-ageing claims are unproven; the clearest positive signal is limited to walking distance in peripheral artery disease.
• !Marketing outpaces evidence: supplements are sold with strong longevity/energy claims that the human data do not support.
• !A 2022 animal study reported NR may promote triple-negative breast cancer growth and metastasis to the brain; unconfirmed in humans but a genuine flag given proliferating cells' high NAD+ demand.
• !Long-term safety in humans is established mainly over weeks-to-months at the doses tested; effects of years of continuous use are unknown.
• !Supplement quality is not regulated as a medicine, so actual NR content and purity can vary between products.
• !Authorised novel-food conditions are for healthy adults and exclude infants and children; pregnant and breastfeeding women are subject to a lower permitted intake.

Not a licensed medicine. Nicotinamide riboside chloride is an authorised novel food in Great Britain (following the EFSA 2019 assessment under Regulation (EU) 2015/2283, retained in UK law), permitted in food supplements for healthy adults, with a lower permitted intake for pregnant and breastfeeding women. It is therefore sold legally as a food supplement (e.g. Tru Niagen) rather than regulated by the MHRA as a medicine, which means it has not undergone the efficacy and safety scrutiny required of a licensed drug and cannot legally be marketed with claims to treat or prevent disease (such claims would fall foul of the Human Medicines Regulations 2012).

• · Phase I/II· Completed

  Chronic NR supplementation in healthy middle-aged and older adults (Martens 2018)

  Raised NAD+ and was well tolerated; only suggestive effects on blood pressure/arterial stiffness.

• · Phase I (safety)· Completed

  NR-SAFE high-dose NR in Parkinson's disease

  High doses tolerable with no methyl-donor depletion; designed to assess safety, not prove benefit.

• · Phase II· Completed

  Nicotinamide riboside for peripheral artery disease (NICE)

  RCT that met its primary endpoint: NR modestly but significantly improved 6-minute walk distance; the strongest positive clinical signal for NR so far.

• · Phase II· Completed

  NR for cognition and symptom recovery in long-COVID

  Double-blind RCT over 24 weeks; NR raised NAD+ several-fold but did not improve cognition, fatigue, sleep or mood versus placebo.

1. 01
   Nicotinamide riboside is uniquely and orally bioavailable in mice and humans — Trammell SAJ et al., Nature Communications (2016)

   First human pharmacokinetic trial; established dose-dependent rise in the blood NAD+ metabolome and NAAD as a repletion biomarker.

2. 02
   Chronic nicotinamide riboside supplementation is well-tolerated and elevates NAD+ in healthy middle-aged and older adults — Martens CR et al., Nature Communications (2018)

   Randomised crossover RCT; NR safely raised whole-blood NAD+ but functional/cardiovascular benefits were modest at best.

3. 03
   What is really known about the effects of nicotinamide riboside supplementation in humans — Damgaard MV, Treebak JT, Science Advances (2023)

   Critical review of 25 human studies concluding NR shows few clinically relevant effects and the literature tends to overstate findings.

4. 04
   The effect of nicotinamide mononucleotide and riboside on skeletal muscle mass and function: a systematic review and meta-analysis — Prokopidis K et al., Journal of Cachexia, Sarcopenia and Muscle (2025)

   Meta-analysis (10 RCTs); NR/NMN did not preserve muscle mass or function in adults over ~60, though it notes the positive PAD walking signal.

5. 05
   NR-SAFE: a randomized, double-blind safety trial of high dose nicotinamide riboside in Parkinson's disease — Brakedal B et al., Nature Communications (2023)

   High-dose NR was tolerable in Parkinson's disease with no methyl-donor depletion; a safety trial rather than a demonstration of efficacy.

6. 06
   Nicotinamide riboside for peripheral artery disease: the NICE randomized clinical trial — McDermott MM et al., Nature Communications (2024)

   RCT in PAD that met its primary endpoint: NR modestly but significantly improved 6-minute walk distance. The strongest positive clinical signal for NR to date.

7. 07
   Safety of nicotinamide riboside chloride as a novel food (EFSA opinion) — EFSA Panel on Nutrition, Novel Foods and Food Allergens, EFSA Journal (2019)

   Basis for UK/EU authorisation of NRC as a novel food in supplements; judged safe for healthy adults at the levels assessed, with a lower limit for pregnancy/lactation.

8. 08
   A bioluminescent-based probe for in vivo non-invasive monitoring of nicotinamide riboside uptake reveals a link between metastasis and NAD+ metabolism — Goun lab (Sazonova EV et al.), Biosensors and Bioelectronics (2022)

   Murine study reporting NR may promote triple-negative breast cancer and brain metastasis; not confirmed in humans but a safety flag.