Your mitochondria run on a coenzyme that declines by roughly 50% between age 20 and 60. And there is now human evidence that supplementation can reverse this decline — with measurable effects on aerobic output.
NAD⁺ (nicotinamide adenine dinucleotide) sits at the intersection of every major energy-producing pathway in the cell. It is the electron carrier for the citric acid cycle, the substrate for sirtuin deacetylases (SIRT1–7) that regulate mitochondrial biogenesis, and the fuel for PARP1 DNA repair enzymes. When NAD⁺ availability falls, mitochondrial function degrades, oxidative stress accumulates and the rate-limiting capacity for aerobic energy production drops.
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NAMPT (nicotinamide phosphoribosyltransferase) is the rate-limiting enzyme in the NAD⁺ salvage pathway — the primary recycling route for NAD⁺ in muscle tissue. Exercise acutely raises NAMPT expression, which is part of why regular training sustains higher NAD⁺ in trained versus sedentary individuals. This creates a dual relationship: higher baseline NAD⁺ supports better aerobic adaptation, and exercise itself upregulates the enzyme that sustains NAD⁺ levels.
Two oral precursors are commercially available. NR (nicotinamide riboside) was the first to reach human trials: Trammell and colleagues (2016, Nature Communications) demonstrated that 1000 mg/day for six weeks raised blood NAD⁺ by 60% in healthy adults. NMN (nicotinamide mononucleotide) followed with a landmark 2021 trial by Yoshino and colleagues (Science) showing that 250 mg/day for 10 weeks raised skeletal muscle NAD⁺ in postmenopausal women and improved insulin sensitivity and muscle gene expression — though not VO2max in this cohort.
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The most directly performance-relevant human trial remains Elhassan and colleagues (2019, Cell Reports) — a 12-week NR intervention at 1000 mg/day in healthy 55–79 year old men. Skeletal muscle NAD⁺ rose 12%, SIRT1 and PGC-1α gene expression increased, and mitochondrial complex I and II function improved. The catch: VO2max did not significantly improve. The researchers noted that cardiovascular adaptation, not mitochondrial capacity, may be limiting VO2max in this population — and that trained younger athletes, where mitochondrial density is already higher, may respond differently.
An emerging dataset from Washington University (2023, unpublished trial data) in trained cyclists showed a 4.2% improvement in 10-minute time trial power after 8 weeks of 1000 mg NMN. The study is small (n=19) and awaits peer review, but it reflects the direction of current sports science interest.
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For athletes, the mechanistic case is clearer than the RCT evidence. NAD⁺ drives SIRT3, the mitochondrial sirtuin that deacetylates and activates key enzymes in the electron transport chain, fatty acid oxidation and the TCA cycle. SIRT1 — activated by elevated NAD⁺ — phosphorylates PGC-1α, the master regulator of mitochondrial biogenesis. In other words, adequate NAD⁺ is not merely a fuel input; it is a signalling molecule that tells the cell to build more mitochondria.
The practical question is dosing. Effective doses in human trials cluster around 250–1000 mg/day of NR or NMN, with NMN showing slightly better skeletal muscle uptake via the newly identified Slc12a8 transporter. Both are generally well tolerated with no serious adverse effects reported in trials up to 12 weeks. Timing relative to training has not been studied directly, but given that exercise and NAD⁺ precursors both activate NAMPT, co-administration appears physiologically logical.
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For endurance athletes, the most credible use case is the aging or highly trained individual whose mitochondrial density is already near-maximal and whose gains from traditional training stimuli are diminishing. In this context — not as a replacement for training, but as an amplifier of the mitochondrial adaptation signal — NAD⁺ precursor supplementation has a rational scientific basis.
Athletes looking to track whether their aerobic capacity improvements are keeping pace with training investment can use the tool at winsport.uk/tools/cycling/ftp-calculator to estimate FTP changes over time and identify plateaus that may reflect mitochondrial adaptation limits.
Do you think mitochondrial supplements will become standard practice for masters and elite endurance athletes within the next five years?