NAD+ (nicotinamide adenine dinucleotide) is a coenzyme found in every cell in the body, required for converting food into usable energy and for activating the enzymes that repair damaged DNA. Levels decline with age, by some estimates roughly halving between early adulthood and age 80, which is why NAD+ has become a central focus of longevity research. This guide explains what NAD+ actually does, why it falls, and what human clinical trials, not just cell or animal studies, show about raising it.
Quick Facts
- What it is: A coenzyme required for cellular energy production and DNA repair
- Why it matters: Levels decline an estimated 50% or more from young adulthood to old age
- How to raise it: Precursor compounds such as nicotinamide riboside (NR), niacinamide, and NMN
- Studied NR doses: 100mg to 2,000mg per day across published human trials
- Evidence level: Well established that precursors raise blood NAD+; downstream health benefits are still an active research area
What NAD+ Does in the Body
NAD+ exists in every cell and cycles constantly between its oxidized form (NAD+) and reduced form (NADH) as part of the electron transport chain, the mitochondrial process that generates ATP, the cell's basic energy currency. Beyond energy metabolism, NAD+ is consumed as a substrate by two other important enzyme families: sirtuins, which regulate gene expression related to metabolism and cellular stress resistance, and PARPs (poly-ADP-ribose polymerases), which detect and help repair damaged DNA. Because NAD+ is used up by these processes rather than just recycled, the body's ability to keep making it is directly relevant to how well cells manage energy demand and repair.
Why NAD+ Declines With Age
Two main mechanisms are thought to drive the age-related decline. First, activity of CD38, an enzyme that consumes NAD+, increases with age and with chronic low-grade inflammation, a phenomenon sometimes called "inflammaging." Second, activity of NAMPT, the rate-limiting enzyme in the pathway that regenerates NAD+ from nicotinamide (the "salvage pathway"), tends to decrease with age. Combined, cells produce less NAD+ while consuming more of it, and the net effect is a gradual, well-documented decline across tissues.
Can You Raise NAD+ Levels? Precursors Explained
Nicotinamide Riboside (NR)
A form of vitamin B3 that converts to NAD+ through a more direct route than plain niacin or niacinamide, without the flushing side effect associated with high-dose niacin. NR is the most extensively studied NAD+ precursor in controlled human trials to date. See our full Nicotinamide Riboside guide.
Niacinamide (Nicotinamide)
The more common, less expensive form of vitamin B3, and a direct precursor in the same salvage pathway as NR. Research suggests it raises blood NAD+ acutely but less durably over time compared with NR at equivalent doses; it also has long-standing, separate research behind it for skin health. See our full Niacinamide guide.
Nicotinamide Mononucleotide (NMN)
A direct precursor one step closer to NAD+ than NR in the metabolic pathway. NMN has a smaller, though growing, base of human clinical trials than NR, and its regulatory status varies by market. It is not currently part of our compound encyclopedia, and mechanistically it behaves similarly to NR, though head-to-head human comparisons remain limited.
NR vs NMN: What the Evidence Shows
Direct comparison trials of NR and NMN in the same participants are still uncommon, but available data suggest both precursors raise circulating blood NAD+ by a similar magnitude over roughly two weeks of use, with nicotinamide alone raising it only briefly. NR currently has a longer track record of published, peer-reviewed long-term safety data at doses up to 1,000-2,000mg per day, including a multi-month randomized safety trial in overweight adults. NMN research has expanded quickly, with human trials in specific populations such as older adults and, more recently, arterial stiffness outcomes, but the overall body of long-duration human safety data remains smaller than for NR as of this writing.
What Human Trials Actually Show
Raising blood NAD+ levels. Evidence level: Established. A 2018 randomized, placebo-controlled crossover trial in healthy middle-aged and older adults found that NR supplementation increased average NAD+ metabolome levels by roughly 60% compared to placebo, and was well tolerated over six weeks. An earlier dose-ranging study found NR raised whole blood NAD+ by approximately 22%, 51%, and 142% at doses of 100mg, 300mg, and 1,000mg per day respectively, showing a clear dose-response relationship.
Long-term safety. Evidence level: Established. A randomized, double-blind, placebo-controlled trial of long-term NR administration in healthy overweight adults found it to be safe and well tolerated, without adverse effects on standard blood chemistry markers.
Downstream health outcomes (blood pressure, cognition, fatigue). Evidence level: Emerging. Trials looking at outcomes beyond raising NAD+ itself, such as blood pressure, arterial stiffness, cognitive performance, and fatigue in specific conditions like long-COVID, are newer and more mixed. A 2025 randomized trial in adults with long-COVID found NR supplementation raised NAD+ levels and was associated with improvements in certain symptom and cognitive measures over 24 weeks, though this is a specific patient population rather than healthy adults in general.
Supporting NAD+ Naturally
Beyond precursor supplements, regular aerobic exercise is one of the most consistently documented ways to support NAD+ metabolism, partly through effects on NAMPT activity. Some longevity researchers also pair NAD+ precursors with sirtuin-activating compounds such as trans-resveratrol, on the theory that more NAD+ substrate paired with more sirtuin activation may be more effective than either alone, though robust human trials on this specific combination are still limited.
Dosage & Safety
Published human trials have studied NR doses ranging from 100mg to 2,000mg per day, with 250-300mg per day being a common starting range in commercial products and 300mg being the dose used in several of the foundational safety and NAD+-raising trials. Reported side effects across trials have been mild and infrequent, and unlike high-dose niacin, NR and NMN do not typically cause skin flushing. As with any supplement intended for long-term daily use, starting at the lower end of the studied range is a reasonable approach.
ⓘ Raising blood NAD+ with a precursor is well supported by human trials. Whether that translates into specific benefits like better energy, cognition, or longevity in healthy adults is still an active area of research, not a settled conclusion.
Frequently Asked Questions
What is NAD+ in simple terms?
NAD+ is a coenzyme every cell needs to convert food into usable energy and to power the enzymes that repair DNA. It's consumed continuously by normal cell function and needs to be regenerated.
Why does NAD+ decline with age?
Two main factors: an age- and inflammation-related enzyme called CD38 breaks down more NAD+, while NAMPT, the enzyme that helps regenerate it, becomes less active. The combination reduces net NAD+ availability over time.
Is NR or NMN better for raising NAD+?
Both raise blood NAD+ by a similar magnitude in short-term trials. NR currently has a longer history of published long-term human safety data, while NMN research is expanding but has a smaller body of long-duration trials as of this writing.
Does raising NAD+ actually slow aging?
Raising blood NAD+ with precursors is well documented. Whether this reliably produces anti-aging benefits in healthy humans, as opposed to specific outcomes in specific studied populations, is still being actively researched and is not yet a settled question.
What is the right dose of NAD+ precursor to take?
Human trials have used anywhere from 100mg to 2,000mg per day of NR, with 300mg per day appearing in several key studies. There's no official Recommended Dietary Allowance, so starting at a lower studied dose and discussing higher doses with a healthcare provider is a reasonable approach.
Scientific References
- Martens, C. R., Denman, B. A., Mazzo, M. R., et al. "Chronic Nicotinamide Riboside Supplementation Is Well-Tolerated and Elevates NAD+ in Healthy Middle-Aged and Older Adults." Nature Communications, 2018;9:1286.
- Airhart, S. E., Shireman, L. M., Risler, L. J., et al. "An Open-Label, Non-Randomized Study of the Pharmacokinetics of the Nutritional Supplement Nicotinamide Riboside (NR) and Its Effects on Blood NAD+ Levels in Healthy Volunteers." PLOS ONE, 2017;12(12):e0186459.
- Conze, D., Brenner, C., Kruger, C. L. "Safety and Metabolism of Long-Term Administration of NIAGEN (Nicotinamide Riboside Chloride) in a Randomized, Double-Blind, Placebo-Controlled Clinical Trial of Healthy Overweight Adults." Scientific Reports, 2019;9:9772.
- Trammell, S. A., Schmidt, M. S., Weidemann, B. J., et al. "Nicotinamide Riboside Is Uniquely and Orally Bioavailable in Mice and Humans." Nature Communications, 2016;7:12948.
- Yang, Y., et al. "An Updated Review on the Mechanisms, Pre-Clinical and Clinical Comparisons of Nicotinamide Mononucleotide (NMN) and Nicotinamide Riboside (NR)." Food Frontiers, 2025.
- Wu, C. Y., Reynolds, W. C., Abril, I., et al. "Effects of Nicotinamide Riboside on NAD+ Levels, Cognition, and Symptom Recovery in Long-COVID: A Randomized Controlled Trial." eClinicalMedicine, 2025.
Disclaimer
This article is for educational purposes only and is not intended to diagnose, treat, cure, or prevent any disease. It does not constitute medical advice and is independent of any specific product or brand. Always consult a qualified healthcare provider before beginning any new supplement regimen, particularly if you are pregnant, breastfeeding, or managing a medical condition.
