NAD+

NAD+ is a pyridine dinucleotide coenzyme, not a peptide, and the central redox carrier of cellular metabolism. It cycles between the oxidised form (NAD+) and the reduced form (NADH); in healthy cells the ratio sits at roughly 700 parts NAD+ to one part NADH, and that ratio governs how efficiently oxidative metabolism runs. It is consumed as a substrate, not merely cycled, by the sirtuins, PARPs, and CD38, so demand rises with DNA damage, inflammation, and immune activation.

ATP turnover is enormous: about 100 grams is held at any moment, roughly 90% of it generated in the electron transport chain where NAD+ is a critical cofactor. Endogenous NAD+ begins declining around the third decade and may fall 50% or more by the 40s. Because NAD+ underpins oxidative metabolism, DNA repair, circadian regulation, and immune function, that decline is implicated in fatigue, impaired repair, metabolic dysfunction, oncogenesis, and neurodegenerative disease including Alzheimer's and Parkinson's.

The link to the sirtuins (SIRT1 through SIRT7), NAD+-dependent deacetylases governing stress response, metabolism, DNA repair, and chromosomal stability, is the mechanistic centre of the longevity interest.

NAD+ can be raised via oral precursors (niacin through the Preiss-Handler pathway; NMN and NR through the salvage pathway), via subcutaneous or intramuscular injection, or via exercise. Injectable NAD+ is supplied lyophilised, in buffered and unbuffered presentations; it is acidic in solution, which is why a buffered presentation exists. It is a large molecule that precipitates at high concentration, so it requires more diluent than most peptides.

NAD+ cycles between its oxidised form and NADH. In glycolysis, cytosolic glucose breakdown yields a small ATP amount plus NADH within milliseconds, sustaining roughly the first 10 seconds of maximal effort before lactate accumulates. In the mitochondrial Krebs cycle, glycolytic products are fully oxidised and most NADH is generated. At the inner-membrane electron transport chain, NADH donates electrons to drive proton pumping and roughly 90% of ATP synthesis, regenerating NAD+. The healthy NAD+:NADH ratio of about 700:1 determines oxidative efficiency; when NAD+ is scarce, energy production is rate-limited and cellular stress rises.

Decline has three drivers. NAD+-consuming enzymes, particularly CD38 and the PARPs, draw more substrate with age as DNA repair and immune processes become less efficient; CD38 expression rises with age and chronic inflammation. NAMPT, the rate-limiting enzyme of the salvage pathway responsible for about 80% of NAD+ synthesis, loses efficiency. Damaged mitochondria recycle NAD+ poorly, establishing a feed-forward loop of reduced NAD+, impaired oxidative output, and further mitochondrial stress.

NAD+ is the obligate co-substrate for SIRT1 through SIRT7, which regulate DNA repair and genomic stability, inflammation, mitochondrial biogenesis, lipid metabolism and insulin sensitivity, and circadian rhythm. It is consumed by PARP enzymes during DNA repair, so accumulated damage and falling NAD+ compound each other.

Direct injection bypasses the biosynthesis pathways entirely: no conversion, no gut deamidation of precursors to nicotinic acid, no flush. Rigorous controlled trials of subcutaneous NAD+ remain limited. Two caveats shape use. Converting precursors to NAD+ requires ATP, so damaged mitochondria may fail to use the substrate, which is the rationale for repairing structure with SS-31 first. And chronic supplementation can suppress NAMPT despite raising NAD+ metabolites, which is why cycling is treated as non-negotiable.

Bioenergetics: NAD+ repletion restores mitochondrial function and oxidative capacity, raising energy output, reducing fatigue, increasing metabolic rate with support for weight loss, improving muscle function, and enhancing skeletal muscle development and mitochondrial health. Preclinical and early human data indicate improved insulin sensitivity and lipid metabolism.

Neurological: protects neurons against oxidative stress and ischaemic insult from insufficient perfusion; maintains and improves cognitive function through energy production, DNA repair, and neuronal sirtuin activation. Users report improved mental clarity and reduced brain fog.

Cardiovascular: reduces atherosclerotic plaque accumulation in arterial walls; restores arterial elasticity; preclinical work shows protection against cardiovascular disease and support for healthy blood pressure.

Genomic maintenance: supplies substrate to PARP-mediated DNA repair, supporting genomic integrity over time.

Longevity and immune: promotes healthy ageing and extends lifespan and healthspan in animal models; improves overall health markers; supports immune activity, itself an NAD+-consuming process. Sirtuin activity is substrate-limited by NAD+ availability, which is the mechanistic argument for repletion.

Recovery: used clinically to support recovery from substance dependence, reducing withdrawal symptoms and supporting brain health during detoxification, under medical supervision only.

First week. Increased energy is commonly reported, more so with injectable routes than oral precursors. Some report improved sleep quality and mental sharpness. Magnitude tracks baseline NAD+ status; those with significant depletion tend to notice more.

Weeks 2 to 4. Sustained energy improvement, better exercise recovery, and cognitive benefits becoming more apparent as repair processes ramp up.

Long term. Cellular-level effects (DNA repair, mitochondrial support, sirtuin activation) accumulate but are not directly perceptible. Continued use maintains elevated NAD+.

After stopping. Levels return to baseline gradually; no withdrawal or rebound, but benefits diminish over weeks to months. Note the NAMPT concern: after chronic uncycled use, endogenous production may sit below the pre-supplementation baseline, which is why on/off cycling is built into the protocol.

Tolerability. Subcutaneous NAD+ is widely described as more uncomfortable than typical peptide injections, with burning or stinging at the site. Slow injection, a slightly larger needle gauge, and warming the solution to room temperature are the usual mitigations. Morning dosing is preferred; later dosing can interfere with sleep.

Non-responders. Conversion of precursors to usable NAD+ requires ATP. Where mitochondria are structurally compromised, substrate alone gives limited results. In practice SS-31 is used first for a repair phase before NAD+ is layered in.

Reconstitution. NAD+ is a large molecule that crystallises or precipitates at high concentration, so the standard 2 mL reconstitution fails. Use 3 mL bacteriostatic water for a 500 mg vial or 6 mL for a 1,000 mg vial; both yield 166.7 mg/mL, so 100 mg is 60 units on an insulin syringe. Vials are typically 10 mL glass. Run diluent down the vial wall, swirl, do not shake. Buffered (pH-adjusted) and unbuffered presentations exist; the unbuffered solution is more acidic and harsher to inject, and older presentations were reconstituted more dilute to compensate. Milligram dosing is identical across presentations; only draw volume changes.

Stability. Refrigerate at 2 to 8 degrees Celsius, protect from light, do not freeze, and use within 14 days rather than the typical 28. Inspect before every dose: cloudiness, discolouration, or particulates indicate precipitation and the vial is discarded.

Loading. Subcutaneous, 100 to 200 mg daily for 7 to 10 consecutive days to restore depleted reserves.

Maintenance. 50 to 100 mg, 1 to 3 times per week. Intramuscular dosing is identical with slightly faster absorption, but the acidic solution burns on injection, causes soreness and stiffness, and carries a high incidence of histamine-type reactions (flushing, chest tightness, throat tingling, cough). Subcutaneous is slower and better tolerated, with erythema, nodules, and transient swelling as its own profile.

Timing. Morning; late dosing may interfere with sleep. Fasting is not required and a light meal alongside the dose minimises side effects in susceptible individuals.

Cycling. 8 to 12 weeks on, 4 to 8 weeks off, to prevent NAMPT suppression and allow salvage-pathway recovery. Exercise during the off-cycle raises NAMPT expression and muscle NAD+ by over 100%.

Ceiling. Cumulative intake above 3,000 mg per month is associated with hepatic damage, renal disease, and vascular complications. A full 200 mg loading phase for 10 days is 2,000 mg before maintenance begins, so the loading phase should be counted against the monthly total. Dose conservatively and escalate only as needed to sustain benefit.

Human evidence rests largely on oral precursors. Multiple trials confirm oral NMN and NR raise blood NAD+ by 40 to 90% with consistent dosing, though tissue-level increases are less well characterised.

The strongest clinical endpoint is Yoshino et al. (Science, 2021): 10 weeks of NMN at 250 mg daily improved skeletal muscle insulin sensitivity in overweight or obese prediabetic women.

The 2024 systematic review and meta-analysis of RCTs in Critical Reviews in Food Science and Nutrition (Li et al., 2024) found NMN significantly elevated blood NAD, but body composition, physical performance, and most metabolic markers did not differ significantly from controls. Substrate repletion does not reliably translate to clinical improvement.

Liu et al. (Science Advances, 2024) showed NR and NMN facilitate NAD+ synthesis via enterohepatic circulation, with gut bacteria deamidating them to nicotinic acid during absorption. Oral precursors are therefore largely functioning as expensive niacin. A 2025 study in healthy men over 40 found liposomal NMN raised NAD+ significantly more than non-liposomal NMN or placebo, suggesting partial bypass.

Niacin feeds the Preiss-Handler pathway directly and remains the cheapest, most proven oral route, limited by flush tolerance.

Direct injection bypasses biosynthesis, gut deamidation, and flush, but rigorous controlled trials on subcutaneous NAD+ are limited; support is largely clinical experience.

NAMPT suppression is the key long-term concern: a human study found NR supplementation decreased NAMPT despite raising NAD+ metabolites, threatening the salvage pathway that produces about 80% of endogenous NAD+. Cycling 8 to 12 weeks on, 4 to 8 weeks off is the mitigation. Exercise raises NAMPT expression and muscle NAD+ by over 100%.

Animal studies show extended lifespan and healthspan, improved physical function, and reversal of some age-related decline; human translation is unproven. Supporting reviews include Yoshino, Baur and Imai (Cell Metabolism, 2018), Martens et al. (Nature Communications, 2018), Elhassan et al. (Cell Reports, 2019), and Covarrubias et al. (Nature Reviews Molecular Cell Biology, 2021).