NAD+: Complete Guide

NAD+ is a dinucleotide composed of two nucleotides joined through their phosphate groups — one containing an adenine nucleobase and the other containing nicotinamide. It exists in two forms: NAD+ (oxidized) and NADH (reduced). This redox pair is fundamental to cellular metabolism, shuttling electrons in reactions that convert nutrients into ATP — the cell's primary energy currency.

Beyond energy metabolism, NAD+ serves as a substrate (not just a cofactor) for three critical enzyme families: sirtuins (SIRT1-7), which regulate gene expression, DNA repair, and cellular stress responses; PARPs (poly ADP-ribose polymerases), which repair damaged DNA; and CD38/CD157, ectoenzymes involved in immune cell signaling. Each of these enzymes consumes NAD+ in the process of functioning, meaning high demand can deplete cellular pools.

The age-related decline in NAD+ has become a central focus of longevity research. Studies in model organisms have shown that restoring NAD+ levels can reverse certain hallmarks of aging, including mitochondrial dysfunction, stem cell exhaustion, and impaired DNA repair capacity.

NAD+ supplementation works through several interconnected mechanisms:

• Sirtuin activation: NAD+ is the required co-substrate for all seven mammalian sirtuins. SIRT1 and SIRT3 are particularly important — SIRT1 deacetylates transcription factors involved in stress resistance, fat metabolism, and inflammation, while SIRT3 regulates mitochondrial protein function. Without adequate NAD+, sirtuin activity declines proportionally.
• DNA repair support: PARP1 and PARP2 consume NAD+ to generate poly(ADP-ribose) chains that recruit DNA repair machinery to damaged sites. Under genotoxic stress, PARP activation can dramatically deplete NAD+ pools, creating a competition between DNA repair and sirtuin-mediated maintenance.
• Mitochondrial function: NAD+ is essential for the citric acid cycle and oxidative phosphorylation. Declining NAD+ impairs mitochondrial electron transport, reducing ATP production and increasing reactive oxygen species (ROS) generation — a self-reinforcing cycle of mitochondrial decline.
• Epigenetic regulation: Through sirtuin-mediated histone deacetylation, NAD+ levels directly influence gene expression patterns. Age-related NAD+ depletion contributes to epigenetic drift — the loss of youthful gene expression patterns.

Aging and Longevity

The most extensive NAD+ research involves aging. Studies in aged mice demonstrated that NAD+ repletion (via precursors like NMN) reversed age-related mitochondrial dysfunction, improved muscle stem cell function, extended lifespan, and restored vascular density to youthful levels. Human trials with NAD+ precursors have shown increases in blood NAD+ levels and improvements in markers of biological age.

Neurodegeneration

NAD+ depletion is observed in Alzheimer's, Parkinson's, and ALS models. Supplementation has shown neuroprotective effects in preclinical studies, potentially through SIRT1-mediated reduction of tau phosphorylation and amyloid processing, and through improved mitochondrial function in neurons.

Metabolic Health

NAD+ influences insulin sensitivity through SIRT1 modulation of glucose and lipid metabolism. Animal studies show NAD+ repletion improves glucose tolerance, reduces hepatic fat accumulation, and enhances mitochondrial fatty acid oxidation. Clinical trials are investigating effects on metabolic syndrome.

Cardiovascular Research

NAD+ supplementation has been shown to protect against cardiac hypertrophy, improve endothelial function, and restore age-related decline in blood vessel density in animal models. These effects are primarily mediated through SIRT1 and SIRT3 activation in cardiac and vascular tissue.

NAD+ is administered through several routes with varying bioavailability:

Route	Typical Research Dose	Frequency	Notes
Subcutaneous injection	100–500 mg	Daily or 2–3× weekly	Direct bioavailability, avoids GI degradation
IV infusion	250–750 mg	1–2× weekly	Clinic-administered, rapid NAD+ repletion
Oral (NMN/NR precursors)	250–1000 mg	Daily	Indirect — requires enzymatic conversion to NAD+

Injectable NAD+ bypasses the oral precursor conversion pathway (NMN → NAD+ or NR → NMN → NAD+), providing more direct restoration of cellular NAD+ pools. For reconstitution guidance, use the peptide calculator. For injection preparation, see the reconstitution guide.

For detailed protocols, visit the NAD+ dosage guide.

NAD+ supplementation has a generally favorable safety profile in published research, though injectable routes carry additional considerations:

• Injection site discomfort: Subcutaneous NAD+ injections commonly produce stinging or burning at the injection site, often described as more uncomfortable than typical peptide injections
• Flushing and warmth: Transient flushing, particularly with higher doses or IV administration
• Nausea: Reported with IV infusions, typically managed by slowing infusion rate
• GI effects: Oral precursors (NMN, NR) may cause mild GI discomfort at higher doses
• Theoretical concerns: Some researchers have raised questions about NAD+ supplementation potentially supporting tumor growth in established cancers, as rapidly dividing cells also require NAD+ — though this remains an area of active investigation

Read more in the NAD+ side effects guide.

Understanding the NAD+ supplementation landscape:

Form	Route	Conversion Steps to NAD+	Key Consideration
NAD+ (direct)	SC injection, IV	0 (direct)	Immediate bioavailability, injection discomfort
NMN	Oral, SC	1 step (NMN → NAD+)	Good oral absorption, widely available supplement
NR (Niagen)	Oral	2 steps (NR → NMN → NAD+)	Most clinical trial data, well-tolerated orally
Niacin (B3)	Oral	Multiple steps	Oldest approach, causes flushing, raises HDL

Injectable NAD+ offers the most direct pathway but requires injection administration. Oral precursors like NMN and NR are more convenient but undergo enzymatic conversion that may be rate-limited. The choice depends on the research context and goals. For other anti-aging peptides, see epitalon (telomerase activation) and SS-31 (mitochondria-targeted).