NAD+

Nicotinamide adenine dinucleotide (NAD+) is a small, ubiquitous coenzyme present in virtually all cells. It primarily functions as an electron carrier in metabolic pathways, accepting electrons to form NADH during glycolysis, the citric acid cycle and oxidative phosphorylation. Beyond redox chemistry, NAD+ is also a substrate for signaling enzymes such as sirtuins, PARPs and ADP-ribosyltransferases, linking it to regulation of DNA repair, protein acetylation and cellular stress responses. Cells synthesize and maintain NAD+ through de novo and salvage pathways using precursors like nicotinamide, nicotinamide riboside (NR) and nicotinamide mononucleotide (NMN). Interest in NAD+ stems from experimental observations that cellular NAD+ levels decline with age in some tissues and that modulating NAD+ metabolism can alter mitochondrial and metabolic phenotypes in models; however, translation to humans remains under active study and is not yet conclusive.

NAD+ has two interrelated roles. As an oxidized cofactor it accepts electrons to form NADH, which is central to ATP production and maintenance of the cellular redox balance. As a substrate, NAD+ is consumed by enzymes that transfer ADP-ribose or remove acetyl groups: sirtuin deacetylases use NAD+ to regulate protein acetylation and mitochondrial biogenesis, while PARP enzymes use NAD+ to signal and repair DNA damage. Enzymes such as CD38 hydrolyse NAD+, lowering cellular pools. Cells restore NAD+ via salvage enzymes (for example NAMPT converting nicotinamide to NMN) and via de novo biosynthesis. Research strategies include supplying precursors, inhibiting NAD+-consuming enzymes, or enhancing salvage, but tissue-specific responses and downstream functional outcomes vary across models.

Research includes biochemical studies, animal models and a growing number of early human trials. In rodents, increasing NAD+ via precursors (NR, NMN) or manipulating salvage enzymes has improved mitochondrial function, metabolic markers, and resilience to some stressors in specific contexts. Human studies are smaller and shorter, often focusing on safety, NAD+ biomarker changes and metabolic endpoints; results are mixed and sometimes inconsistent. Investigations also explore NAD+ modulation for neurodegenerative, cardiovascular and age-related conditions, but evidence remains preliminary. Key limitations are variable precursor pharmacology, heterogeneous study designs, short follow-up, and limited tissue-specific human data.

Clinically, NAD+ is primarily relevant as a biological target and a rationale for supplementing precursors such as NR or NMN. Available human data do not establish NAD+ restoration as a validated therapy for specific diseases. Short-term trials report acceptable tolerability in many participants, but long-term safety, effects in vulnerable populations, interactions with medications, and product quality vary and are not well characterized. Routine clinical measurement of tissue NAD+ is not established. Healthcare professionals should consider current evidence limitations and discuss potential benefits, uncertainties and regulatory status with patients who are using or considering NAD+-related supplements.