Constantly feeling tired or fatigued? Not the kind of tired a weekend fixes. The kind where you sleep seven hours, wake up already negotiating with the day, and find yourself doing mental arithmetic at 2pm about whether you can get away with a third coffee.
Most men over 40 misdiagnose this. They blame the job, the kids, the late nights, the fact that they're "just getting older." Then they treat it with caffeine, which borrows energy from the evening and charges interest. The exhaustion never actually resolves — it just moves around the day.
Persistent fatigue has many possible causes, including sleep disorders, anaemia, thyroid disease, medication effects, depression, and cardiometabolic conditions. Age-related changes in cellular energy metabolism are one research area, not a default diagnosis. Rule out common medical causes before treating fatigue as a supplement problem.
Why Male Energy Falls Off a Cliff in Your Forties
Every cell in your body runs on ATP — adenosine triphosphate, the molecule your muscles, heart and brain spend to do anything at all. ATP is manufactured inside mitochondria, and mitochondria are the part of you that ages most visibly at a biochemical level.
Three things happen to them over time, and they compound:
Mitochondrial density drops. Muscle biopsy studies consistently show fewer functioning mitochondria per cell in older adults than in younger ones. Fewer factories, less output.
NAD⁺ falls. NAD⁺ is the coenzyme that lets mitochondria run the reactions that produce ATP in the first place. Tissue NAD⁺ concentrations decline substantially with age across multiple mammalian species, including humans. Without adequate NAD⁺, the machinery is intact but under-fuelled.
Damage accumulates faster than repair. Mitochondria generate reactive oxygen species as an unavoidable by-product of doing their job. Antioxidant defences that used to neutralise them get overwhelmed, and damaged mitochondria produce less energy and more damage.
That is why the fatigue feels different from ordinary tiredness. It isn't a sleep debt. It's a supply problem — and it shows up first in the two tissues with the highest energy demand per gram: your brain and your skeletal muscle. Which is precisely why the two symptoms men report together are brain fog and legs that feel heavy on stairs they used to take two at a time.
Supplements for Mental and Physical Energy: The Compounds With Actual Human Data
The energy supplement aisle is mostly stimulants wearing lab coats. What follows is narrower — compounds that act on the ATP production pathway itself, with the honest state of evidence attached to each.
1. NAD⁺ precursors — refilling the tank
If NAD⁺ decline is the bottleneck, raising NAD⁺ is the obvious lever. There are several ways to do it, and they are not equivalent.
NMN is the most studied precursor in humans. In a randomised, placebo-controlled trial published in Science, Yoshino and colleagues (2021) gave 250 mg of NMN daily to prediabetic postmenopausal women for ten weeks and measured a significant improvement in skeletal muscle insulin sensitivity — direct evidence that an NAD⁺ precursor changes how human muscle handles fuel. Human trial
NMNH is the reduced, hydrogen-bearing form. In cell and rodent work, Zapata-Pérez and colleagues (2021) found NMNH raised NAD⁺ faster and to higher peak levels than equivalent NMN, apparently by entering the salvage pathway through a different route. It is a genuinely promising compound and the reason it sits at the centre of the Longevity Complex™. It is also, at time of writing, without published human trials — the enhanced potency is established in animals and cells, not yet in people. Preclinical
NADH skips the queue entirely. Rather than a precursor your body must convert, NADH is the reduced coenzyme itself, donating electrons directly into the mitochondrial electron transport chain. The human data here is older and specific: Forsyth and colleagues (1999) ran a double-blind crossover trial in chronic fatigue syndrome patients and reported symptomatic improvement on NADH versus placebo. The trial was small. But it is human, controlled, and it is fatigue. Human trial
2. Ubiquinol — the form that actually absorbs
Coenzyme Q10 shuttles electrons between complexes in the respiratory chain. No CoQ10, no ATP. Your body's own production of it declines from roughly your twenties onward, and statins suppress it further by blocking the same mevalonate pathway that makes cholesterol — which is why muscle fatigue and cramping are among the most common statin complaints.
The important distinction is form. Standard CoQ10 (ubiquinone) is oxidised and must be reduced before use, and absorption is poor. Ubiquinol arrives pre-reduced.
The strongest evidence here is Q-SYMBIO (Mortensen et al., 2014) — a multicentre randomised controlled trial in chronic heart failure patients where CoQ10 supplementation significantly reduced major adverse cardiovascular events over two years. Human trial That study used ubiquinone, not ubiquinol, and it was a disease population, so read it as evidence that CoQ10 does something real in human mitochondria under stress — not as a promise about your Tuesday afternoon.
3. PQQ — building new mitochondria rather than fuelling old ones
PQQ works on a different axis. Instead of improving output from existing mitochondria, PQQ has been shown in cell and animal models to activate PGC-1α signalling, the master regulator of mitochondrial biogenesis — the process by which cells build additional mitochondria. Mechanism Small human studies have reported changes in fatigue and sleep measures. The mitochondrial biogenesis finding itself remains largely preclinical.
4. Urolithin A — clearing out the broken ones
There's a step most energy protocols miss. Damaged mitochondria don't politely retire; they linger, producing little ATP and considerable oxidative stress. Mitophagy is the recycling process that removes them, and it slows with age.
Urolithin A is a metabolite produced from ellagitannins by particular gut microbes, and production varies substantially between people. In a four-month randomised trial in older adults, Urolithin A improved some muscle-endurance measures, while the co-primary six-minute walk and maximal ATP-production outcomes were not significantly different from placebo. Human trial, mixed outcomes Direct supplementation avoids relying on uncertain microbial conversion, but it does not guarantee a functional benefit.
How These Fit Together: Fuel, Spark, Factory, Cleanup
The reason a stack tends to outperform any single compound is that these four mechanisms are sequential, not redundant.
| Role | Compound | What it addresses | Best evidence |
|---|---|---|---|
| Fuel | NMN / NMNH | Low NAD⁺ availability | RCT (NMN) / preclinical (NMNH) |
| Spark | NADH | Immediate electron donation | Small human crossover |
| Transport | Ubiquinol | Electron chain efficiency | Large RCT (heart failure) |
| Factory | PQQ | Mitochondrial number | Preclinical + small human |
| Cleanup | Urolithin A | Damaged mitochondria | RCT, muscle endurance |
Buying five compounds separately means five orders, five shipments and a digital scale on your kitchen counter. The Energy Complex™ combines the fatigue-focused compounds in single daily doses; the broader Longevity Complex™ adds the DNA-maintenance and autophagy compounds for men working on healthspan rather than energy alone.
See the Energy Complex™ →Rule Out the Boring Explanations First
This matters more than anything above. Persistent fatigue in men over 40 has several common medical causes that no supplement will fix, and delaying a blood test to try a powder is a genuinely bad trade.
Ask your doctor for: full blood count and ferritin (iron deficiency is not only a women's issue), TSH and free T4 (thyroid), HbA1c or fasting glucose, vitamin D, B12, and total plus free testosterone drawn in the morning. Sleep apnoea is dramatically underdiagnosed in men and produces exactly this symptom picture — if you snore and wake unrefreshed, get assessed.
Get those cleared. Then work on the mitochondrial side, where the ceiling is genuinely higher than most men realise.
How long before anything changes?
Be sceptical of anyone promising a week. NAD⁺ repletion is measurable in blood within days, but the downstream effects people actually feel — steadier afternoon energy, better recovery between training sessions — realistically take four to eight weeks. Urolithin A's muscle endurance trial ran four months. Mitochondrial remodelling is slow biology. Judge it at eight weeks, not eight days.
References
Yoshino M, et al. Nicotinamide mononucleotide increases muscle insulin sensitivity in prediabetic women. Science. 2021;372(6547):1224–1229. Human trial
Zapata-Pérez R, et al. Reduced nicotinamide mononucleotide is a potent NAD⁺ precursor. FASEB J. 2021;35(4):e21456. Preclinical
Forsyth LM, et al. Therapeutic effects of oral NADH on the symptoms of patients with chronic fatigue syndrome. Ann Allergy Asthma Immunol. 1999;82(2):185–191. Human trial
Mortensen SA, et al. The effect of coenzyme Q10 on morbidity and mortality in chronic heart failure (Q-SYMBIO). JACC Heart Fail. 2014;2(6):641–649. Human trial
Singh A, et al. Effect of Urolithin A supplementation on muscle endurance and mitochondrial health in older adults. JAMA Netw Open. 2022;5(1):e2144279. Human trial, mixed outcomes
These statements have not been evaluated by the Food and Drug Administration. These products are not intended to diagnose, treat, cure or prevent any disease. Persistent fatigue can indicate an underlying medical condition — consult a qualified healthcare professional before starting any supplement, particularly if you take prescription medication.
