NAD+: Research & Studies

Research Overview#

The research literature on NAD+ has expanded rapidly over the past decade, driven by the discovery that NAD+ levels decline with age and that NAD+ replenishment can reverse multiple hallmarks of aging in preclinical models. The clinical evidence base is growing but remains mostly in the early-phase trial stage.

Key Clinical Studies#

Nicotinamide riboside in healthy older adults (Martens et al., 2018)

• Design: Randomized, double-blind, placebo-controlled crossover trial
• Population: 24 lean, healthy men and women aged 55-79
• Intervention: NR 500 mg twice daily (1000 mg/day) for 6 weeks, with 6-week washout
• Key findings: NR raised whole blood NAD+ approximately 60% from baseline, was well tolerated with no serious adverse events, and showed trends toward reduced systolic blood pressure and aortic stiffness. This was one of the first well-controlled human trials demonstrating that oral NR reliably raises NAD+ in older adults.

NR in skeletal muscle aging (Elhassan et al., 2019)

• Design: Open-label, single-arm study with muscle biopsies
• Population: 12 aged men (70-80 years)
• Intervention: NR 1000 mg/day for 21 days
• Key findings: NR increased skeletal muscle NAD+ metabolite levels and induced anti-inflammatory transcriptomic signatures. This study provided the first direct evidence that oral NR supplementation alters the NAD+ metabolome in human skeletal muscle.

NR safety at high doses (NR-SAFE trial)

• Design: Randomized, double-blind, placebo-controlled
• Population: 52 healthy middle-aged and older adults
• Intervention: NR 2000 mg/day for 12 weeks
• Key findings: Established safety and tolerability of NR at the highest dose tested in a controlled trial. No clinically significant adverse events were attributed to NR.

NR in Parkinson's disease (NOPARK trial)

• Design: Phase II, randomized, double-blind, placebo-controlled
• Population: 30 Parkinson's disease patients
• Intervention: NR 1000 mg/day for 30 days
• Key findings: NR increased cerebral NAD+ levels measured by MRS and showed some improvements in MDS-UPDRS clinical scores. This represents one of the first controlled trials targeting a neurodegenerative disease with NAD+ augmentation.

First-in-human NMN study (Irie et al., 2020)

• Design: Open-label, single-arm safety and pharmacokinetics
• Population: 10 healthy Japanese men
• Intervention: NMN 250 mg single dose
• Key findings: NMN was safe, well tolerated, and raised plasma NAD+ metabolites. This established the feasibility of oral NMN supplementation in humans.

Key Preclinical Studies#

NAD+ and aging (Imai and Guarente laboratories)

• Shin-ichiro Imai's laboratory demonstrated that NAMPT (the rate-limiting enzyme in the NAD+ salvage pathway) declines with age in multiple tissues in mice, and that NMN supplementation reverses age-related metabolic decline, improves insulin sensitivity, and enhances physical activity in aged mice.
• Leonard Guarente's laboratory established the connection between NAD+ and sirtuin biology, showing that caloric restriction extends lifespan partly through increased NAD+ availability and sirtuin activation.

CD38 as a driver of NAD+ decline (Chini laboratory)

• Eduardo Chini's laboratory identified CD38 as the dominant NADase responsible for age-related NAD+ decline. CD38 expression increases with age and chronic inflammation, and CD38 knockout mice maintain youthful NAD+ levels into old age.
• This work established CD38 inhibition as a potential therapeutic strategy complementary to NAD+ precursor supplementation.

SARM1 and axonal degeneration

• SARM1 was identified as an NADase activated during axonal injury, rapidly depleting axonal NAD+ and triggering Wallerian degeneration. SARM1 inhibitors are being developed for neurodegenerative diseases and traumatic nerve injury.

NMN in Alzheimer's disease models

• NMN supplementation reduced amyloid-beta production and accumulation, improved synaptic plasticity, and rescued cognitive deficits in APP/PS1 transgenic mouse models of Alzheimer's disease. These findings have motivated the ongoing human trials in neurodegenerative conditions.

Systematic Reviews and Meta-Analyses#

• A systematic review of human clinical trials of NAD+ precursors (NR and NMN) found consistent evidence for NAD+ metabolite elevation across studies but insufficient data to draw conclusions about clinical efficacy for any specific disease indication.
• Evidence quality is limited by small sample sizes (most trials n<50), short duration (most <12 weeks), and reliance on surrogate biomarker endpoints rather than clinically meaningful outcomes.

Ongoing Clinical Trials#

Multiple clinical trials are currently registered investigating NAD+ precursors:

• NR in heart failure (NCT03423342)
• NMN in aging and metabolic health (multiple trials in the US, Japan, and China)
• IV NAD+ in substance use disorders (multiple centers)
• NR in kidney disease and AKI recovery
• NMN in exercise performance and body composition

Research Methodology#

The NAD+ research field benefits from strong mechanistic understanding of NAD+ biology and well-validated preclinical models. However, translation to human clinical evidence faces several challenges:

• Most human trials use blood NAD+ metabolites as primary endpoints rather than disease-specific clinical outcomes
• The relationship between blood NAD+ levels and tissue NAD+ levels in specific organs (brain, heart, liver) is incompletely understood
• Placebo effects and natural variation in NAD+ levels complicate interpretation of small trials
• Diverse formulations, doses, and routes of administration make cross-study comparisons difficult

Evidence Quality Assessment#

The evidence base for NAD+ currently spans:

• Systematic reviews/meta-analyses: Emerging; primarily summarizing biomarker outcomes
• Randomized controlled trials (human): Multiple completed for NR; emerging for NMN; very limited for IV NAD+
• Animal studies: Extensive body of research across aging, neurodegeneration, metabolic disease, and cardiovascular models
• In vitro studies: Extensive mechanistic work on NAD+-dependent enzymes and pathways
• Case reports/series: Available for IV NAD+ in addiction medicine

Related Reading#

• NAD+ overview and research guide
• NAD+ dosing protocols
• NAD+ molecular structure