What the Research Shows on NAD+: Ageing, Precursor Trials and NAD+ Itself

NAD+ is not a peptide but a dinucleotide of about 663 daltons (PubChem): a nicotinamide nucleotide and an adenine nucleotide joined through their phosphate groups. Interest rests on two ideas: that it falls with age, and that restoring it matters. This review covers what is published as of October 2026.

What NAD+ does

NAD+ has two roles. As a redox cofactor it accepts electrons from the breakdown of fuels, becoming NADH, which passes them to the mitochondrial electron transport chain. As a substrate it is used up: sirtuins consume it to remove acetyl and related groups from proteins, PARPs to build poly(ADP-ribose) chains during DNA repair, and the NADases CD38, CD157 and SARM1 break it down. Each reaction releases nicotinamide, which the salvage pathway recycles through NMN back to NAD+; nicotinamide riboside (NR) joins the same route via NMN (Covarrubias et al., 2021). In mice, NAD+ turnover varied widely between tissues: fast in the small intestine and spleen, slow in skeletal muscle (Liu et al., 2018). Surplus nicotinamide can also be cleared by methylation, covered in our NNMT inhibitor article.

Does NAD+ decline with age?

In mice, mostly yes, though less than often implied. Across tissues of aged mice NAD+ was a median of about 30% lower, with production intact and turnover slightly faster, pointing to greater consumption rather than failing synthesis (McReynolds et al., 2021).

Human data are thinner and tissue-specific. Magnetic resonance spectroscopy found lower NAD+ in the brains of older healthy volunteers (Zhu et al., 2015). In a cross-sectional study, muscle NAD+ was lower in older adults, lowest in the physically impaired and closer to young levels in exercise-trained older adults, and it tracked daily step count (Janssens et al., 2022).

This is where the picture is mixed. A 2021 review of studies in yeast, worms, rodents, monkeys and humans found the evidence for an overall decline very limited, often from a single tissue and weakest in humans, and noted that analytical variability may explain some differences between laboratories (Peluso et al., 2021). In 2026, a validated mass spectrometry method applied to seven independent human cohorts found whole-blood NAD+ stable with age and across lifestyle interventions, though it rose with NR (Trętowicz et al., 2026).

The precursor route: NR and NMN in human trials

Most human work uses precursors, and the route matters: in mice, NR and NMN given intravenously reached tissues intact, but given orally they were largely converted to nicotinamide in the liver (Liu et al., 2018).

What they raised. NR raised NAD+ in circulating immune cells by about 60% against placebo in a crossover trial of 30 healthy middle-aged and older adults (Martens et al., 2018), and a 2026 systematic review of 33 human intervention studies found that oral NR and NMN consistently raised NAD+ or related metabolites in blood (Gallagher et al., 2026). Tissue is less consistent. In 12 older men, NR doubled muscle NAAD, a sensitive marker of NAD+ synthesis, without raising muscle NAD+ itself (Elhassan et al., 2019); in 25 women with prediabetes, NMN left muscle NAD+ unchanged (Yoshino et al., 2021). In a trial in 30 people with newly diagnosed Parkinson's disease, NR raised brain NAD by a variable amount on magnetic resonance spectroscopy (Brakedal et al., 2022).

What they changed. In a trial of 40 obese, insulin-resistant men, 12 weeks of NR did not improve insulin sensitivity, glucose metabolism, energy expenditure or body composition (Dollerup et al., 2018). One positive result came from NMN: muscle insulin sensitivity was 25% higher after 10 weeks in the 13 women given it, with no change on placebo (Yoshino et al., 2021). In the Parkinson's trial, those whose brain NAD rose showed altered brain metabolism, associated with mild clinical improvement (Brakedal et al., 2022). The 2026 review judged effects on functional, metabolic and vascular outcomes heterogeneous and often null (Gallagher et al., 2026). NOPARK, a phase 3 trial of NR in 410 people with early Parkinson's disease, was completed in June 2025 according to its ClinicalTrials.gov record; we found no published results as of 2 October 2026.

NAD+ given directly

NAD+ itself has been studied far less than its precursors, and the human evidence is small.

• Pharmacokinetics. In a pilot of 11 men (eight received NAD+, three saline), plasma NAD+ did not rise for the first two hours of a six-hour intravenous infusion, then peaked about 400% above baseline at six hours. The metabolites pointed to breakdown by NAD+-cleaving enzymes, NAD+ itself appeared in urine, and no adverse events were recorded. The study was part-funded by NAD+ Research Inc., and one author directs a clinic that uses intravenous NAD+ (Grant et al., 2019).
• Tolerability. A retrospective review of records at a commercial infusion clinic compared six clients given intravenous NAD+ with eight given intravenous NR. All six NAD+ recipients reported moderate to severe symptoms during infusions, including abdominal cramping, nausea, vomiting, a faster heart rate and chest pressure, which stopped when the infusions ended. The authors were employed by the clinic (Reyna et al., 2026).
• Heart failure. Two single-centre randomised trials in China gave NAD+ intravenously for seven days alongside standard treatment. In 60 hospitalised patients, using an NAD+ product approved in China, changes in NT-proBNP and ejection fraction favoured NAD+ but were not statistically significant (Pei et al., 2024). In 180 patients with ischaemic cardiomyopathy, ejection fraction at one month was modestly higher with NAD+ (45.4% versus 42.4%), with only non-significant trends in NT-proBNP, clinical events and functional class (Yu et al., 2026).

A 2026 systematic review found no eligible outcome trials of intravenous or intramuscular NAD+ for anti-ageing or wellness uses (Gallagher et al., 2026). Reviewing NAD for compounded medicines in 2019, the US FDA found the nonclinical data inadequate to characterise its toxicity and too little clinical data to judge its safety (Federal Register, 2019).

Stability and handling in solution

NAD+ is chemically fragile. The oxidised form undergoes base-catalysed breakdown at high pH, while the reduced form, NADH, is broken down by acid instead (Wolfe et al., 2024). Heat adds to this: in one biocatalysis study, free NAD+ in solution lost half its activity in about 35 hours at 37 °C and in about 18 minutes at 100 °C (McDonough et al., 2025). In another, a rise of just 6 °C clearly sped up NADH breakdown, and the buffer mattered: at pH 8.5 both forms lasted longer in Tris than in phosphate or HEPES (Wolfe et al., 2024). The FDA's 2019 review added that NAD degrades substantially on exposure to light, moisture, alkaline pH or ordinary room temperature.

This chemistry is the rationale for buffering NAD+ preparations and for keeping material cold, dry and out of the light. It describes the molecule, not any product: a vial's label and certificate of analysis are the record of its contents.

The bottom line

NAD+ biology is well established; the ageing story less so. The fall with age is real in many mouse tissues and in some human tissues, but modest, uneven and absent from human whole blood. Precursors reliably raise blood NAD+ in human trials, yet effects on outcomes remain mostly unproven. NAD+ given directly is the least studied route, and in the laboratory its sensitivity to pH, heat, moisture and light is the constant.

References

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