Medical Disclaimer: This article is for informational purposes only and does not constitute medical advice. Always consult a qualified healthcare professional before starting any supplement regimen or making changes to your health routine. The information presented here is based on published research but should not replace professional medical guidance.
I’ve followed the NAD+ science closely for over a decade, and I think it represents one of the most compelling areas in all of longevity biology. Not because of hype — NAD+ has attracted plenty of that — but because the underlying mechanism is genuinely fundamental. This isn’t a supplement targeting one narrow pathway. It’s a molecule that sits at the centre of how your cells produce energy, repair DNA, and regulate gene expression.
When NAD+ levels fall — and they fall significantly with age — the downstream consequences touch virtually every hallmark of ageing. Understanding NAD+ is, in many ways, understanding ageing itself.
In this guide, I’ll explain what NAD+ is, why it declines, what happens when it does, and the most evidence-based approaches to restoring it.
What Is NAD+ and Why Does It Decline?
NAD+ (nicotinamide adenine dinucleotide) is a coenzyme found in every living cell. It exists in two forms — NAD+ (oxidised) and NADH (reduced) — and cycles between them as it carries electrons during metabolic reactions. This redox cycling is central to how mitochondria generate ATP from food.
But NAD+ does far more than shuttle electrons. It’s the essential substrate for three major classes of enzymes that directly regulate ageing:
- Sirtuins (SIRT1–7): A family of deacetylases that regulate gene expression, stress responses, mitochondrial function, and inflammation. Often called “longevity genes” — their activity is entirely NAD+-dependent.
- PARPs (poly ADP-ribose polymerases): Enzymes that detect and repair DNA damage. PARP1 alone consumes enormous amounts of NAD+ when DNA damage is high.
- CD38: A glycohydrolase involved in immune function and calcium signalling that degrades NAD+. CD38 expression increases dramatically with age and is a primary driver of NAD+ decline.
The Decline With Age
NAD+ levels fall by approximately 50% between age 20 and 60 — a decline seen consistently across multiple tissues including blood, muscle, liver, and brain.[4] This isn’t a gradual linear decline — it accelerates with age and is compounded by metabolic disease, obesity, alcohol consumption, and excessive sun exposure (all of which increase PARP activation and thus NAD+ consumption).
Why Does NAD+ Fall So Dramatically?
The primary culprit is CD38 — an enzyme whose expression roughly doubles between youth and old age. CD38 degrades NAD+ as part of its signalling function, and as its expression rises, NAD+ is consumed faster than it can be replenished through the biosynthesis pathways. Chronic low-grade inflammation (inflammaging) also upregulates CD38, creating a vicious cycle: low NAD+ impairs sirtuin activity, which worsens inflammation, which drives more CD38, which depletes more NAD+.
Why NAD+ Matters for Longevity
The “NAD+ World” hypothesis, developed through the work of David Sinclair at Harvard and Leonard Guarente at MIT, proposes that declining NAD+ is a master driver of the ageing process — not merely a consequence of it.[4]
Sirtuin Activation
Sirtuins are among the most studied longevity-associated proteins in biology. In yeast, worms, and mice, increasing sirtuin activity extends lifespan. SIRT1 and SIRT3 in particular regulate mitochondrial biogenesis, fatty acid oxidation, inflammation, and the cellular stress response. When NAD+ falls, sirtuin activity falls with it — and the downstream consequences include reduced mitochondrial quality, impaired DNA repair, and increased inflammation.
DNA Repair Capacity
DNA damage accumulates continuously throughout life — from UV radiation, reactive oxygen species, and replication errors. PARP enzymes detect and repair this damage, but their activity is entirely dependent on NAD+. When NAD+ is low, DNA repair capacity is compromised. Conversely, Gomes et al. demonstrated in a landmark 2013 Cell paper that restoring NAD+ in aged mice — by boosting it via NMN — restored PARP1 activity and improved DNA repair markers to levels comparable to young mice.[4]
Mitochondrial Function
NAD+ is a co-substrate for complex I of the mitochondrial electron transport chain. Low NAD+ directly impairs ATP production, contributing to the energy deficits, fatigue, and muscle weakness associated with ageing. Restoring NAD+ improves mitochondrial biogenesis and function in animal models — and increasingly, in human trials.
How to Boost NAD+ Levels
There are four main strategies for raising NAD+ levels, which can be combined for greater effect:
- Supplementing NAD+ precursors — NMN, NR, or niacin (see below)
- Inhibiting CD38 — apigenin and quercetin both inhibit CD38, reducing NAD+ degradation
- Exercise — particularly Zone 2 cardio, which activates NAMPT (the rate-limiting enzyme in the NAD+ salvage pathway)
- Fasting and caloric restriction — upregulate SIRT1 and AMPK, improving NAD+ metabolism
Direct oral NAD+ supplementation is generally not effective — the NAD+ molecule is too large to cross cell membranes intact and is broken down in the gut before reaching the bloodstream in meaningful quantities. Precursor molecules (NMN, NR) are smaller, more bioavailable, and are converted to NAD+ inside cells.
NMN vs NR vs Niacin: Comparing the Precursors
| Compound | How It Raises NAD+ | Human Evidence | Tolerability | Cost |
|---|---|---|---|---|
| NMN (Nicotinamide Mononucleotide) | Direct NAD+ precursor; converted via NMNAT enzymes | Multiple RCTs — improved muscle insulin sensitivity, aerobic capacity, sleep quality | Excellent — no flushing | High |
| NR (Nicotinamide Riboside) | Converts to NMN then to NAD+ | Multiple human trials — consistently raises NAD+ in blood; metabolic benefits | Excellent — no flushing | Moderate-high |
| Niacin (Nicotinic Acid) | Via Preiss-Handler pathway | Extensive — cardiovascular data going back decades | Causes flushing at doses >50mg | Very low |
| Niacinamide (Nicotinamide) | Via salvage pathway | Good safety data; effective at raising NAD+ but may inhibit sirtuins at high doses | Excellent — no flushing | Very low |
My Recommendation
For most people focused on longevity, NMN or NR are the practical choices. Both reliably raise NAD+ without side effects. NMN has slightly more recent human trial data and is what David Sinclair uses personally; NR has more accumulated human safety data. At matched doses, the difference in efficacy is likely small for most people. The choice often comes down to cost and product quality.
For a deep comparison, see: NMN Supplement Review
What About CD38 Inhibitors?
Apigenin (found in parsley, chamomile) and quercetin are natural CD38 inhibitors that reduce NAD+ degradation. Some longevity researchers take these alongside NMN/NR on the basis that reducing degradation is as valuable as increasing production. The human evidence for this combination is limited, but the mechanism is sound and both compounds have good safety profiles at typical supplementation doses.
Natural Ways to Support NAD+
Supplementation aside, several lifestyle interventions meaningfully support NAD+ levels:
Exercise
Exercise — particularly sustained aerobic activity — upregulates NAMPT (nicotinamide phosphoribosyltransferase), the rate-limiting enzyme in the NAD+ salvage pathway. Zone 2 cardio is especially effective. A well-exercised person in their 60s may have higher NAD+ levels than a sedentary person in their 40s. See the Zone 2 Cardio Guide.
Caloric Restriction and Fasting
Caloric restriction and intermittent fasting activate SIRT1 and AMPK, which improve NAD+ metabolism and increase the efficiency of the salvage pathway. The NAD+-boosting effect of fasting is part of why intermittent fasting has such broad effects on longevity biomarkers.
Tryptophan-Rich Foods
The de novo biosynthesis pathway converts tryptophan to NAD+ via the kynurenine pathway. Adequate dietary tryptophan (found in turkey, chicken, fish, eggs, dairy, and soya) supports this route. It’s not a replacement for precursor supplementation but contributes to overall NAD+ balance.
Limit NAD+ Consumers
Alcohol, excessive UV exposure, and DNA-damaging stressors all increase PARP1 activation and accelerate NAD+ consumption. Reducing these lifestyle NAD+ drains supports endogenous levels.
Dosage & Supplementation Guide
Please consult your GP before starting NAD+ precursor supplementation, especially if you are on prescription medications or have a history of cancer.
NMN
- Typical range: 250–500mg once daily
- Higher doses: Some researchers (including Sinclair) use 1,000mg/day — safe in trials but expensive and not clearly more effective for most people than 500mg
- Timing: Morning — NAD+ has circadian rhythm involvement and morning dosing aligns with natural patterns
NR
- Typical range: 250–500mg once daily
- Most studied dose: 300mg/day in the earliest human pharmacokinetic trials
- Timing: Morning
Niacin (if using for NAD+ rather than cardiovascular)
- Start at 50–100mg and titrate up slowly to manage flushing
- Extended-release forms reduce flushing but carry more hepatotoxicity risk at high doses
- This approach is generally only appropriate under medical supervision
Side Effects & Safety
NMN and NR have excellent safety profiles based on available human data:
- NMN: No serious adverse events reported in human trials at doses up to 1,200mg/day. Occasional mild GI symptoms at higher doses.
- NR: Extensive safety data — no serious adverse events at doses up to 2,000mg/day in trials. Occasional mild flushing or GI symptoms.
Important Cautions
- Cancer history: NAD+ supports cellular energy metabolism and DNA repair — which benefits healthy cells but may theoretically also support cancer cell survival. This is an active research question. Anyone with a history of cancer should discuss NAD+ supplementation with their oncologist before starting.
- Pregnancy and breastfeeding: Insufficient safety data — avoid.
- High-dose niacinamide: May inhibit sirtuins at doses above ~500mg, potentially counteracting the intended longevity benefit. Stick to lower doses if using niacinamide.
Frequently Asked Questions
What is the best way to increase NAD+ levels?
The most evidence-based approach combines multiple strategies: supplementing NMN or NR (250–500mg/day), regular Zone 2 aerobic exercise (which upregulates NAMPT), intermittent fasting or caloric restriction, and minimising NAD+ consumers like alcohol and excessive sun exposure. No single intervention is as effective as the combination. For supplementation specifically, NMN and NR are the most practical and well-tolerated options.
Is NMN or NR better for raising NAD+?
Both reliably raise blood NAD+ levels in human trials. NMN has more recent human clinical data and is what David Sinclair uses. NR has more accumulated safety data. Head-to-head comparisons are limited, but the available evidence suggests broadly similar efficacy at matched doses. The choice often comes down to cost, product quality, and personal response. Some people try both and choose based on how they feel.
Can you get enough NAD+ from food?
Food provides NAD+ precursors (tryptophan, niacin from meat, fish, legumes) that contribute to NAD+ synthesis. However, dietary precursor amounts are far below what’s needed to meaningfully reverse the age-related decline in NAD+. Exercise and fasting are more powerful natural boosters than food alone. For people specifically targeting NAD+ restoration as a longevity intervention, supplementation with NMN or NR is the practical route.
How long does it take for NAD+ supplements to work?
Blood NAD+ levels rise within hours of taking NMN or NR, and consistent elevation is seen within 2–4 weeks of daily supplementation. Functional effects — improved energy, sleep quality, metabolic markers — typically emerge over 4–12 weeks in clinical trials. The longevity benefits (if they parallel what’s seen in animal models) would accumulate over years rather than weeks. NAD+ supplementation is a long-term strategy, not a quick fix.
Does David Sinclair take NMN?
Yes — David Sinclair has publicly stated that he takes 1g of NMN daily, alongside resveratrol, metformin (prescription), and other supplements. He is transparent that his personal regimen is experimental and ahead of the clinical evidence. His use of NMN reflects the strength of his own research and conviction in the mechanism, but it’s worth noting that 1g/day is significantly higher than the doses studied in most published human trials (250–500mg).
Citations
- Yoshino M, Yoshino J, Kayser BD, et al. Nicotinamide mononucleotide increases muscle insulin sensitivity in prediabetic women. Science. 2021;372(6547):1224-1229. PMID: 33378629
- Mills KF, Yoshida S, Stein LR, et al. Long-term administration of nicotinamide mononucleotide mitigates age-associated physiological decline in mice. Cell Metab. 2016;24(6):795-806. PMID: 28068668
- Cantó C, Houtkooper RH, Pirinen E, et al. The NAD+ precursor nicotinamide riboside enhances oxidative metabolism and protects against high-fat diet-induced obesity. Cell Metab. 2012;15(6):838-847. PMID: 22682224
- Gomes AP, Price NL, Ling AJ, et al. Declining NAD+ induces a pseudohypoxic state disrupting nuclear-mitochondrial communication during aging. Cell. 2013;155(7):1624-1638. PMID: 24360282
- Trammell SA, Schmidt MS, Weidemann BJ, et al. Nicotinamide riboside is uniquely and orally bioavailable in mice and humans. Nat Commun. 2016;7:12948. PMID: 27721479
- López-Otín C, Blasco MA, Partridge L, Serrano M, Kroemer G. Hallmarks of aging: An expanding universe. Cell. 2023;186(2):243-278. PMID: 36599349
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Last reviewed: 14 Apr 2026 by Steve Butler, Health Writer & Longevity Researcher