Mitochondria, NAD, and Fatigue: Evidence and Caveats

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• NAD+ does two jobs, which is why its decline shows up as more than tiredness. It drives the redox reactions that transfer electrons to produce ATP, and it serves as a substrate for sirtuins and PARPs, the enzymes handling DNA repair and stress response regulation. So falling NAD+ with age produces sluggish mitochondrial function, accumulating DNA damage and slower recovery from exertion — and the cognitive version, the sense that your brain is not as sharp, runs on the same mechanism.
• The NMN versus NR question has a specific resolution. NMN is a direct precursor converted through the enzyme NAMPT, and its bioavailability was long doubted on the assumption it had to convert to NR before entering cells — a belief overturned by the discovery of the Slc12a8 transporter carrying it directly. A 2021 study found NMN supplementation improved aerobic capacity and oxygen use in older adults. NR is the more established compound in human research, with a 2016 study significantly raising NAD+ in middle-aged and older adults and improving metabolic function without adverse effects, alongside neuroprotective signals.
• The practical distinctions between them come down to evidence depth and availability. NR has the longer human track record, particularly for metabolic and cognitive outcomes, is typically less expensive and more widely available. NMN's results are promising but weighted toward animal models and early human trials, and it is marketed more heavily toward endurance and muscle recovery. Dr. Lin also flags a regulatory shift worth knowing: NMN is being investigated as a drug, and the FDA has signalled it does not want it sold over the counter, so US availability is likely to change.
• Dose ranges in the literature are wide enough to be uninformative on their own — anywhere from 250 mg to over 1,000 mg daily for both NMN and NR, with studies supporting most points in between. The reassuring part is that no significant adverse effects have emerged across that range. The caveat is that some people do get nausea, headaches or, counterintuitively, increased fatigue, which is Dr. Lin's argument for telling your doctor even about an over-the-counter supplement.
• A useful piece of context: NR is an alternate form of vitamin B3. Niacin, the better-known form, was used far more historically but causes the notorious facial flushing that made it unpopular; NR does not appear to. Dietary sources of these precursors exist — avocados, broccoli, cabbage, tomatoes, raw beef — but at roughly half a milligram to one milligram per 100 grams, which makes food an impractical route to a therapeutic dose.
• CoQ10's evidence is strongest for fatigue specifically. A systematic review of randomised controlled trials confirmed that supplementation significantly reduced fatigue scores, with larger effects at higher doses over longer durations, across a range including chronic fatigue patients, athletes and older adults. It also shows promise for mitochondrial function, oxidative stress and endothelial function, with better outcomes in heart failure — though effects on blood pressure and cholesterol are considerably less clear.
• Dr. Lin's explanation for why CoQ10 remains contested is worth generalising. Her view is that the field does not study specific enough use cases at specific enough doses in specific enough populations, so broad trials produce muddy answers to questions that were never sharply posed. She names this as a structural problem across health and longevity research rather than something particular to CoQ10.
• Ubiquinol is the reduced form of CoQ10 and considerably more bioavailable, which matters most for the people who need it most — older adults and anyone with absorption difficulties, since the body's ability to convert ubiquinone into ubiquinol declines with age. A double-blind placebo-controlled study found 100-150 mg daily improved energy levels and cognitive task performance in healthy people with only mild fatigue, and animal work showed reduced serum lactate and creatine kinase after exercise. Typical dosing runs 100-300 mg daily, with the upper end associated with better exercise performance and recovery.
• The statin interaction is the most clinically actionable item here: statins deplete CoQ10. Dr. Lin is emphatic that statins remain a very important tool for anyone dealing with dyslipidemia and should not be abandoned — but pairing them with CoQ10 can mitigate the mitochondrial depletion they cause, which is why some practices combine them routinely.
• PQQ's distinguishing claim is biogenesis rather than efficiency — it stimulates the creation of new mitochondria by activating CREB and PGC-1α. Animal studies showed it prolonged time to exhaustion during exercise while reducing oxidative stress markers and protecting mitochondrial integrity. It carries neuroprotective signals, protecting neurons from cell death and raising ATP in brain tissue, with human studies linking it to cognitive improvement and reduced inflammatory markers, plus metabolic effects on lipid metabolism and glucose tolerance in animals. Typical dosing is 10-20 mg daily, with 20 mg associated with fatigue reduction — though Dr. Lin notes the brain-health literature used markedly different units and recommends working through that variability with a professional.
• Urolithin A has the cleanest human trial evidence of the four. Produced by gut microbiota metabolising ellagic acid and ellagitannins from pomegranates, berries and nuts, it works by inducing mitophagy — selectively clearing damaged mitochondria. It enhanced mitochondrial respiratory capacity and exercise performance in rodents and extended lifespan in C. elegans, and a randomised controlled trial published in JAMA Network Open found older adults taking it showed improved muscle endurance and reductions in biomarkers of mitochondrial dysfunction. It also reduces inflammatory markers including CRP and certain plasma ceramides, with emerging work on a gut-muscle axis. The trial-supported dose is 500 mg daily.

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