NAD+ Therapy — The Longevity Protocol Backed by the Best Science We Have

What NAD+ is and why it declines with age

NAD+ is one of the most abundant and critical molecules in your body. It exists in every living cell and participates in over 500 enzymatic reactions. Its two primary roles: shuttling electrons during cellular energy production (the mitochondrial electron transport chain) and serving as a substrate for enzymes that repair DNA, regulate gene expression, and modulate immune response.

As you age, NAD+ levels drop — roughly 50% between ages 40 and 60. This decline is driven by increased consumption (your cells use more NAD+ for DNA repair as damage accumulates) and decreased production (the enzymes that synthesize NAD+ become less efficient). The result is a cellular energy crisis: mitochondria produce less ATP, DNA repair slows, and the sirtuins — a family of longevity-associated proteins — can't function optimally without their NAD+ fuel.

This isn't speculation. NAD+ decline is measurably associated with age-related metabolic dysfunction, neurodegeneration, cardiovascular disease, and impaired immune function. The question isn't whether NAD+ matters — it's whether replenishing it can slow or reverse these processes.

Injectable vs oral: the bioavailability question

The supplement industry has responded to NAD+ research with a flood of oral products — NAD+ capsules, NMN, NR (nicotinamide riboside), and various other precursors. Here's the problem: oral NAD+ is almost entirely degraded in the gastrointestinal tract before it reaches your bloodstream.

NMN and NR are better — they survive digestion and serve as precursors your body can convert into NAD+. But that conversion requires enzymatic steps that become less efficient with age (the exact population that needs NAD+ the most). Oral bioavailability is estimated at 20-30% for NR and potentially lower for NMN in practice.

Intramuscular (IM) injection bypasses the gut entirely. The NAD+ is delivered directly into muscle tissue, absorbed into the bloodstream, and available for cellular uptake without degradation or conversion losses. This is why IV NAD+ clinics have proliferated — but IV infusions take 2-4 hours and cost $500-1,500 per session. IM injection delivers comparable bioavailability in 30 seconds at a fraction of the cost.

The sirtuins connection

Sirtuins are a family of seven proteins (SIRT1-7) that regulate cellular health — DNA repair, inflammation, mitochondrial function, and stress resistance. They've been called "longevity genes" because activating them in animal models consistently extends healthspan and lifespan.

The catch: sirtuins are NAD+-dependent enzymes. They literally cannot function without NAD+ as a co-substrate. When NAD+ levels fall, sirtuin activity falls with them — regardless of whether the sirtuin genes are present and intact. This is the bottleneck that NAD+ replenishment aims to address.

SIRT1 and SIRT3 are particularly relevant. SIRT1 regulates metabolic flexibility, insulin sensitivity, and inflammation. SIRT3 lives in the mitochondria and maintains oxidative phosphorylation efficiency. Both require abundant NAD+ to function — and both decline in activity with age in direct correlation with NAD+ levels.

What the research actually shows

Honesty matters here. The NAD+ longevity space has been driven significantly by David Sinclair's research at Harvard, which demonstrated remarkable lifespan extension in mice treated with NAD+ precursors. Those results are real — but mice are not humans, and the translation is incomplete.

What we know from human data: NR supplementation raises blood NAD+ levels in humans (Martens et al., 2018). NMN supplementation improves insulin sensitivity and muscle function in prediabetic women (Yoshino et al., 2021). IV NAD+ infusion rapidly replenishes intracellular NAD+ stores and has shown subjective improvements in energy, cognition, and recovery in clinical observations.

What we don't yet know: Whether raising NAD+ levels in healthy humans extends lifespan. The long-term dose-response curve for injectable NAD+. Whether the animal model results — which are dramatic — translate proportionally to humans.

The mechanistic rationale is strong. The animal data is compelling. The early human data is promising. But we won't oversell it. NAD+ therapy is a bet on the best available science — not a guaranteed outcome.

Marrow's NAD+ protocol

Marrow's NAD+ protocol uses intramuscular injection — self-administered at home after initial guidance from your physician. The typical protocol is 2-3 injections per week, with dosing adjusted based on your response and goals.

Stacking: the comprehensive longevity protocol

NAD+ addresses cellular energy and DNA repair. But longevity is multifactorial. Marrow's comprehensive longevity protocol combines NAD+ with complementary interventions that target different aging pathways:

• NAD+ + Sermorelin: Sermorelin stimulates natural growth hormone release, supporting muscle maintenance, fat metabolism, sleep quality, and tissue repair. Combined with NAD+, it addresses both the cellular energy crisis and the hormonal decline that accelerates aging.
• NAD+ + Microdose GLP-1: Sub-therapeutic GLP-1 dosing reduces systemic inflammation, improves insulin sensitivity, and optimizes metabolic flexibility. Paired with NAD+'s mitochondrial support, this stack targets metabolic aging from multiple angles. Learn more about microdosing GLP-1.
• Full stack: NAD+ + Sermorelin + microdose GLP-1 for patients who want the most comprehensive longevity approach available through telehealth. Bundled pricing available.

Explore all longevity protocols or start your intake to discuss stacking with a physician.