Longevity Supplements for Endurance Athletes

A marathon block drains iron stores, depletes glycogen and pushes mitochondria to their limit week after week. Supplements for endurance athletes are one of the fastest-growing categories in UK sports nutrition — and most of what is sold is unnecessary.

Wider context sits in our longevity supplements guide and the anti aging supplements range. For the NAD⁺ compounds masters athletes ask about most, see NMN benefits, side effects and dosage, the NMN supplements collection and NMN Pro 1000.

This guide separates the small number of ergogenic aids with genuine performance data from the rest, covers the deficiencies that quietly ruin seasons, and assesses the newer mitochondrial compounds against what has actually been measured in trained humans.

What endurance athletes actually need

Endurance sport is fundamentally an aerobic energy problem. Performance depends on how much oxygen you deliver to working muscle, how efficiently mitochondria convert that oxygen and fuel into ATP, and how well you clear metabolic by-products at intensity.

The four legitimate roles of a supplement

The International Olympic Committee's consensus statement on dietary supplements groups them into four categories, and this remains the most useful framework for an athlete facing a shelf [1].

Anything that does not fit one of these four is unlikely to change your finishing time. That filter explains why our review of longevity supplements that don't work overlaps heavily with the sports nutrition products that quietly disappeared from elite teams a decade ago.

Why endurance athletes are different

Higher iron turnover

Repetitive foot strike causes mechanical haemolysis, sweat carries iron out, and the hormone hepcidin rises after hard sessions, blunting iron absorption for hours afterwards. Iron deficiency is consequently far more common in this group than in sedentary people [3,4].

Elevated and chronic oxidative stress

High aerobic flux generates reactive oxygen species. Some of that signal is essential — it drives mitochondrial adaptation. Blunting it with high-dose antioxidants can reduce training gains, which is why the "more antioxidants" instinct backfires here [2].

Very high energy availability requirements

Long training weeks make it easy to slip into low energy availability, which impairs bone health, endocrine function and immunity [3]. No supplement compensates for under-fuelling, and our explainer on the hallmarks of ageing makes clear why chronic energy deficit accelerates rather than delays decline.

The evidence hierarchy

Not all evidence is equal. Before spending money, place any product on this ladder.

1. Multiple randomised controlled trials in trained humans, with meta-analysis. The standard for caffeine, nitrate and bicarbonate [2,5,11].
2. A small number of RCTs in trained humans. Promising, but effect sizes often shrink with replication. NMN and urolithin A sit here for exercise outcomes [5,12,13,14].
3. RCTs in untrained or clinical populations. Useful for safety, weak for performance inference.
4. Rodent or cell studies only. Hypothesis-generating. Nothing more.
5. Mechanism plus marketing. A plausible pathway is not a result.

The UK market is full of tier 4 and tier 5 products sold with tier 1 confidence. Our explainer on how long supplements take to work is a useful companion, because unrealistic timelines are a main reason athletes abandon compounds that were working.

Tier 1: strong performance evidence

Caffeine

Caffeine is the single best-supported ergogenic aid in endurance sport. It reduces perception of effort, increases time to exhaustion and improves time-trial performance across a wide range of durations. The US National Institutes of Health Office of Dietary Supplements notes that caffeine is more likely to help endurance-type activity than short anaerobic efforts, and that people not habituated to it may see larger effects [2].

Practical protocol

• 3–6 mg per kg body weight, 45–60 minutes before the effort [2,3].
• Lower doses (under 3 mg/kg) during long events, ideally alongside carbohydrate.
• Trial it in training first. Gastrointestinal distress and elevated heart rate are common at the top of the range.

Dietary nitrate (beetroot)

Nitrate is converted to nitric oxide, improving vascular function and reducing the oxygen cost of submaximal exercise. An umbrella review of twenty systematic reviews with meta-analyses found consistent ergogenic effects on time to exhaustion, though results for peak and mean power output were more mixed [5]. A separate umbrella review concluded that meaningful effects generally require supplementation 2–3 hours before exercise, or chronic loading for at least three days, at doses around 8.3–16.4 mmol nitrate [6].

Who benefits most

Recreational and sub-elite athletes tend to respond more strongly than highly trained elites, who already have efficient nitric oxide signalling [5,6]. A separate meta-analysis found benefit specifically for high-intensity interval work, which is the format where the buffering and oxygen-cost effects are most likely to show [8]. Antibacterial mouthwash disrupts the oral bacteria needed to reduce nitrate, so avoid it on race day.

Sodium bicarbonate

Bicarbonate buffers hydrogen ions and is most useful for efforts in the 45-second to 8-minute range — a track 1500m, a pursuit, a hilly cyclocross lap. A meta-analysis focused on closed-end performance tests in that time domain examined 25 bicarbonate studies and found it among the better-supported legal ergogenic aids for intense endurance work [11]. Gastrointestinal upset is the main limitation; split dosing and enteric-coated formats reduce it.

Beta-alanine

Beta-alanine raises muscle carnosine, another intracellular buffer. Like bicarbonate, its benefit concentrates in efforts of roughly one to ten minutes and in the finishing kick of longer races [1,3]. It requires chronic loading — typically 3.2–6.4 g daily for four to twelve weeks — rather than acute dosing. Harmless paraesthesia (skin tingling) is common and dose-dependent.

Creatine

Creatine's clearest effects are on power and repeated sprints rather than steady-state aerobic performance. Endurance athletes benefit indirectly: it supports the strength work that protects against injury, aids glycogen storage, and helps preserve lean mass through heavy blocks and into masters age [1,3]. See NMN vs creatine and creatine for longevity. The small increase in body water can matter for weight-sensitive climbers and runners.

Carbohydrate and electrolytes

Not glamorous, not optional. Carbohydrate remains the highest-return intervention in endurance nutrition, with modern gut-training protocols pushing intakes to 90–120 g per hour in long events using glucose–fructose blends [3]. Sodium replacement matters for high sweat rates and long durations in heat. Everything else in this article is a refinement on top of fuelling and hydration — never a substitute.

Tier 2: fixing deficiencies

This is where most endurance athletes find their biggest single gain, because a deficiency is not a marginal gain — it is a handbrake.

Iron

Iron deficiency is the most consequential nutritional problem in endurance sport, and it frequently exists without anaemia. A systematic review of 23 studies covering 669 female athletes across 16 sports found that iron deficiency impairs endurance performance by 3–4%, and that performance improved by 2–20% when deficient athletes were treated with around 100 mg per day of elemental iron for up to 56 days [4]. The same review noted that maximal aerobic capacity improved by 6–15% following supplementation, and that up to 60% of female athletes experience iron deficiency [4].

A case study of internationally competitive but non-professional female endurance athletes found that 46% had serum ferritin below the athlete-specific threshold of 30 µg/L, despite none meeting the standard clinical definition of deficiency [9].

Test before you supplement

USA Triathlon's clinical guidance notes that standard laboratory reference ranges for ferritin start as low as 10–20 ng/mL, but that a higher cut-off of 40–50 ng/mL is more appropriate for identifying performance-limiting deficiency in endurance athletes [10]. Note that the systematic review above used a threshold of 40 µg/L to define deficiency [4] — thresholds vary between sources, which is precisely why this is a conversation with a clinician rather than a self-diagnosis.

Absorption tips

• Take iron in the morning, away from hard training, when hepcidin is lowest.
• Pair with vitamin C; avoid tea, coffee and calcium at the same time.
• Alternate-day dosing is often better tolerated and better absorbed than daily dosing.

Vitamin D

Vitamin D supports bone mineralisation, muscle function and immune resilience — all under pressure in high-volume training. UK athletes are particularly exposed: the NHS advises that between October and early March, sunlight in the UK is not strong enough for the body to make vitamin D, and recommends everyone consider a daily supplement containing 10 micrograms (400 IU) through autumn and winter [15,16]. Athletes training indoors, before dawn, or with darker skin should consider year-round supplementation. Check status with a vitamin D blood test.

Magnesium

Magnesium is involved in ATP metabolism, muscle contraction and sleep quality, and requirements rise with heavy sweat losses. Form matters more than dose for most athletes: our comparison of magnesium threonate vs glycinate explains why glycinate is usually the better evening choice, which is where the practical benefit lies. See also apigenin vs magnesium for sleep.

Vitamin B12 and plant-based athletes

Vegan and largely plant-based endurance athletes need to plan for B12, iron, iodine, omega-3 (EPA/DHA from algal oil) and often creatine — all lower or less bioavailable in plant-based diets [1,3]. Our guide to vegan longevity supplements maps out a sensible baseline.

Tier 3: mitochondrial and longevity compounds

The newest frontier, and the most relevant to masters athletes. The logic is straightforward: endurance performance is limited by mitochondrial function, and mitochondrial function declines with age. Compounds supporting mitochondrial quantity, quality and turnover are a rational target — provided expectations stay proportionate to the evidence.

NMN and NAD⁺ precursors

NAD⁺ is a coenzyme central to the tricarboxylic acid cycle and oxidative phosphorylation — literally the chemistry of aerobic energy production. NAD⁺ levels fall with age, and NMN is its immediate precursor.

The most directly relevant human trial randomised 48 recreationally trained runners aged 27–50 into placebo, 300 mg, 600 mg or 1,200 mg NMN daily for six weeks alongside structured training. The 600 mg and 1,200 mg groups showed greater improvements in oxygen uptake measures and ventilatory thresholds than placebo, with no adverse effects reported at doses up to 1,200 mg per day [12].

Practical considerations

• Typical athlete doses fall in the 500–1,000 mg range; see NMN dosage by age.
• Timing is generally morning or pre-training — see when to take NMN and NMN with food.
• Methylation support is a common question; see do I need TMG with NMN.
• For the sceptical case, read is NMN a scam? and our UK buying guide.

Urolithin A

Urolithin A is a gut-microbiome metabolite of ellagitannins found in pomegranates and walnuts, which stimulates mitophagy — the clearance and recycling of damaged mitochondria. In a randomised, double-blind, placebo-controlled trial published in JAMA Network Open, 1,000 mg daily significantly improved skeletal muscle endurance in older adults at two months compared with placebo, and improved biomarkers of mitochondrial health — though it missed its primary endpoint of six-minute walk distance [13]. A separate four-month trial in overweight middle-aged adults reported improvements in muscle strength and exercise performance measures [14].

An eight-week randomised trial in resistance-trained male athletes given 1 g daily found favourable shifts in inflammatory and oxidative stress markers, though strength changes did not reach statistical significance in a small sample [17]. A dedicated athlete trial examining urolithin A, skeletal muscle function, iron metabolism and endurance performance has also been registered [18]. See our urolithin A UK guide, Mitopure review and urolithin A vs NMN.

CoQ10, ubiquinol and PQQ

Coenzyme Q10 is an electron carrier in the mitochondrial respiratory chain and an endogenous antioxidant. Production declines with age, and statin users are depleted further. Evidence for direct performance enhancement in young healthy athletes is weak, but the case is more defensible in masters athletes and statin users [2]. See CoQ10 vs ubiquinol and PQQ vs CoQ10.

Taurine, Ca-AKG and NAC

Taurine is concentrated in skeletal muscle and heart tissue and involved in calcium handling; human performance data are mixed and effect sizes small, though safety is good — see taurine and longevity. Calcium alpha-ketoglutarate feeds into the TCA cycle but human performance data remain thin — see our Ca-AKG guide.

N-acetylcysteine supports glutathione synthesis. The same logic that makes it attractive for recovery is why it needs care: suppressing the oxidative signal after training may blunt adaptation, for the same reason high-dose vitamins C and E do [2]. Most athletes who use it reserve it for competition phases, illness or unusually high load rather than base training. See our NAC supplement guide and GlyNAC overview.

What to skip

High-dose antioxidant vitamins

The most important "don't" on the list. Exposure of cells to high concentrations of antioxidant supplements — vitamins C and E have the most evidence — appears to blunt cell signalling and inhibit some favourable physiological adaptations to exercise [2]. Mega-dosing can reduce the training adaptations you are working for. Food-level antioxidant intake is fine and desirable; gram-doses around training are not.

BCAAs in isolation

Branched-chain amino acids are useful arriving as part of complete protein. Isolated BCAA powders provide an incomplete amino acid profile and rarely add anything for an athlete already hitting 1.4–2.0 g protein per kg body weight daily [1,3].

Proprietary blends

If a label lists a blend without disclosing individual doses, you cannot tell whether actives are present at effective levels. Our article on supplement fillers explains what is often making up the difference.

Ketone esters

Genuinely interesting biochemistry, extremely expensive, and an inconsistent performance literature — some studies show impaired high-intensity performance [2]. Not a sensible early purchase.

Building your stack by athlete type

Building from scratch: our guide to starting longevity supplements, minimal supplement stack and budget longevity stack give three templates. For total spend, see longevity stack costs in the UK. Also relevant: men over 50 and women over 40.

Timing, dosing and stacking

Acute vs chronic supplements

Endurance supplements split cleanly into two groups, and confusing them is the most common practical mistake.

Our supplement timing chart maps this visually, and our guides on supplements on an empty stomach and taking supplements together answer the common follow-ups.

Interactions worth knowing

• Calcium, zinc and coffee all reduce iron absorption — separate by at least two hours.
• Fat-soluble vitamins (D, E, K) absorb better with a meal containing fat.
• Bicarbonate and caffeine together increase GI risk; test the combination in training.
• Antibacterial mouthwash blunts nitrate conversion — skip it before a beetroot-supported race [5].

Shift workers and irregular schedules

Athletes training around night shifts face additional circadian and recovery challenges. See supplements for shift workers.

Safety and anti-doping risk

Contamination is the real risk

The Informed Sport certification programme states that up to 1 in 10 supplements on the market are contaminated with a stimulant or steroid prohibited by the World Anti-Doping Agency [7]. That figure comes from a commercial certifier, so read it with that interest in mind — but it is corroborated by independent peer-reviewed work: a clinical review in Sports Health concluded that poor manufacturing processes and intentional contamination with banned substances continue to occur, with weight-loss and muscle-building products at greatest risk [19].

For any athlete subject to testing — including age-group athletes at qualifying events and armed forces personnel — this outranks efficacy. Anti-doping operates on strict liability: the athlete is responsible regardless of intent. Look for batch-tested certification on the actual product you buy, not just the brand.

Compound-specific cautions

If you are considering stopping a compound mid-season, see what happens when you stop taking NMN and cycling NMN.

Choosing a quality product in the UK

Non-negotiables

• Batch-level banned substance testing if you compete under anti-doping rules [7].
• A published certificate of analysis for identity, purity and heavy metals — see how to read a certificate of analysis.
• Third-party testing rather than in-house claims — see third-party tested supplements.
• Fully disclosed doses, no proprietary blends.
• Cost per effective dose, not cost per bottle — see why supplements are expensive.

Where NMN fits

For athletes prioritising mitochondrial energy production, NMN is currently the NAD⁺ precursor with the most directly relevant trained-human data [12] — which is a statement about a thin field rather than a strong one. Purity and dose transparency matter enormously here, so review our tested NMN range and the evidence summary in our NMN benefits, side effects and dosage guide before purchasing. Athletes preferring alternative formats can compare sublingual NMN and liposomal NMN.

Don't neglect the free interventions

Sleep, consistent aerobic volume, strength training twice weekly and adequate energy intake outperform every supplement in this article by a wide margin. Our guide to Zone 2 training and longevity and our overview of biological age put supplementation in its proper context — the final 5%, not the foundation.

When to speak to a doctor

Speak to your GP, pharmacist or a registered sports dietitian before starting any new supplement if you take prescription medication, have a chronic health condition, are pregnant, trying to conceive or breastfeeding, or are under 18. Iron in particular should never be started without blood tests confirming deficiency.

Seek medical assessment rather than reaching for a supplement if you have persistent unexplained fatigue, breathlessness disproportionate to effort, a resting heart rate that has risen markedly, unintended weight loss, recurrent illness or repeated stress injuries. Those can indicate low energy availability, iron deficiency anaemia, thyroid dysfunction or overtraining — all of which need diagnosis rather than supplementation. A Full Body MOT Health Check, ferritin test or thyroid panel gives your GP something to work with.

Never delay seeking medical advice because of something you have read here, and never stop or reduce prescribed medication in pursuit of a training or supplement protocol.

Frequently asked questions

What are the best supplements for endurance athletes?

The best-supported are caffeine (3–6 mg/kg pre-exercise), dietary nitrate from beetroot (roughly 8.3–16.4 mmol, 2–3 hours before or loaded for three or more days), sodium bicarbonate for efforts of 45 seconds to 8 minutes, and beta-alanine for high-intensity buffering [2,5,6,11]. Alongside these, correcting iron and vitamin D deficiency often produces the largest real-world improvement [4,15].

Do endurance athletes need supplements at all?

No supplement is essential if diet, sleep and training are well managed. But endurance athletes have genuinely elevated risk of iron and vitamin D insufficiency due to high iron turnover and limited UK sunlight [4,15], and in those cases supplementation corrects a real limiter rather than adding a marginal gain. Performance supplements are optional refinements on a sound nutritional foundation.

Does NMN improve endurance performance?

A six-week randomised, double-blind, placebo-controlled trial in 48 amateur runners aged 27–50 found that 600 mg and 1,200 mg daily, combined with structured training, improved oxygen uptake and ventilatory threshold measures compared with placebo, with no adverse effects reported [12]. That is promising but represents a single modestly sized trial measuring physiological thresholds rather than race results. Treat NMN as a supportive mitochondrial compound, not a proven ergogenic aid on the level of caffeine.

How much iron should an endurance athlete take?

Only after testing. Research in deficient female athletes has used around 100 mg of elemental iron daily for up to 56 days, with endurance performance improving 2–20% [4]. But iron supplementation without confirmed deficiency is unnecessary and potentially harmful. Ask your GP for ferritin, full blood count, transferrin saturation and CRP, and note that athlete-specific ferritin thresholds (40–50 ng/mL) sit above standard clinical cut-offs [10].

Should endurance athletes take antioxidant supplements?

Generally no, at least not in high doses. Evidence summarised by the NIH Office of Dietary Supplements indicates that high concentrations of antioxidant supplements — particularly vitamins C and E — can blunt the cell signalling that drives beneficial training adaptations [2]. Antioxidants from whole foods are beneficial; gram-scale supplemental doses around training may reduce the adaptations you are training for.

Is creatine useful for runners and cyclists?

It does not directly improve steady-state aerobic performance, but it benefits endurance athletes indirectly by supporting strength and power work, aiding glycogen storage and helping preserve lean muscle mass — particularly valuable for masters athletes [1,3]. The trade-off is a small increase in body water, which weight-sensitive climbers and runners should factor in.

When should I take beetroot juice before a race?

Acute dosing works best 2–3 hours before the event, or load chronically for at least three days beforehand, at doses around 8.3–16.4 mmol nitrate [6]. Avoid antibacterial mouthwash on race day, since it kills the oral bacteria required to convert dietary nitrate into nitrite and then nitric oxide [5].

Are supplements safe for drug-tested athletes?

Only if batch-tested. Informed Sport states that up to 1 in 10 supplements may be contaminated with substances prohibited in sport [7], and independent peer-reviewed review confirms contamination remains an ongoing problem [19]. Anti-doping applies strict liability — the athlete is responsible regardless of intent. Check certification against the specific batch number of the product you are taking.

Can I take NMN and creatine together?

Yes. They act through different mechanisms — NMN supports NAD⁺-dependent mitochondrial energy metabolism, creatine supports the phosphocreatine system — with no known interaction. Our comparison of NMN vs creatine explains why they are complementary rather than redundant.

How long before I notice results?

It depends on the mechanism. Caffeine, nitrate and bicarbonate work acutely, within hours [2,6,11]. Creatine takes one to four weeks depending on loading. Beta-alanine requires four to twelve weeks. Iron correction typically takes eight to twelve weeks to restore ferritin [4]. NMN and urolithin A trials have run six weeks to four months before measuring outcomes [12,13,14], so judge them over a training block rather than a week.

References

1. Maughan RJ, Burke LM, Dvorak J, et al. IOC Consensus Statement: Dietary Supplements and the High-Performance Athlete. International Journal of Sport Nutrition and Exercise Metabolism. 2018;28(2):104–125. https://journals.humankinetics.com/view/journals/ijsnem/28/2/article-p104.xml
2. National Institutes of Health, Office of Dietary Supplements. Dietary Supplements for Exercise and Athletic Performance — Health Professional Fact Sheet. https://ods.od.nih.gov/factsheets/ExerciseAndAthleticPerformance-HealthProfessional/
3. Vitale K, Getzin A. Nutrition and Supplement Update for the Endurance Athlete: Review and Recommendations. Nutrients. 2019;11(6):1289. https://www.mdpi.com/2072-6643/11/6/1289
4. Pengelly M, Pumpa K, Pyne DB, et al. Iron deficiency, supplementation, and sports performance in female athletes: A systematic review. Journal of Sport and Health Science. 2025;14:101009. https://pubmed.ncbi.nlm.nih.gov/39536912/
5. Dietary Nitrate Supplementation and Exercise Performance: An Umbrella Review of 20 Published Systematic Reviews with Meta-analyses. Sports Medicine. https://pmc.ncbi.nlm.nih.gov/articles/PMC12106159/
6. Effects of Beetroot Juice on Physical Performance in Professional Athletes and Healthy Individuals: An Umbrella Review. https://pmc.ncbi.nlm.nih.gov/articles/PMC12195723/
7. Informed Sport (LGC). Setting the Gold Standard — The Pillars of the Informed Sport Programme. https://sport.wetestyoutrust.com/news/setting-gold-standard-pillars-informed-sport-programme
8. The Effect of Beetroot Ingestion on High-Intensity Interval Training: A Systematic Review and Meta-Analysis. Nutrients. 2021. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8618171/
9. High Prevalence of Iron Deficiency Exhibited in Internationally Competitive, Non-Professional Female Endurance Athletes — A Case Study. International Journal of Environmental Research and Public Health. 2022. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9778947/
10. USA Triathlon. Iron Strength: What Endurance Athletes Should Know About Iron Deficiency Anemia and Ferritin Screening. https://www.usatriathlon.org/articles/training-tips/what-endurance-athletes-should-know-about-iron-deficiency-anemia-and-ferritin-screening
11. Caffeine and Bicarbonate for Speed: A Meta-Analysis of Legal Supplements Potential for Improving Intense Endurance Exercise Performance. Frontiers in Physiology. 2017. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5422435/
12. Liao B, Zhao Y, Wang D, et al. Nicotinamide mononucleotide supplementation enhances aerobic capacity in amateur runners: a randomized, double-blind study. Journal of the International Society of Sports Nutrition. 2021;18(1):54. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8265078/
13. Liu S, D'Amico D, Shankland E, et al. Effect of Urolithin A Supplementation on Muscle Endurance and Mitochondrial Health in Older Adults: A Randomized Clinical Trial. JAMA Network Open. 2022;5(1):e2144279. https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2788244
14. Singh A, D'Amico D, Andreux PA, et al. Urolithin A improves muscle strength, exercise performance, and biomarkers of mitochondrial health in a randomized trial in middle-aged adults. Cell Reports Medicine. 2022;3:100633. https://www.sciencedirect.com/science/article/pii/S2666379122001586
15. NHS. Vitamins and minerals — Vitamin D. https://www.nhs.uk/conditions/vitamins-and-minerals/vitamin-d/
16. GOV.UK. Vitamin D supplementation during winter: PHE and NICE statement. https://www.gov.uk/government/publications/vitamin-d-supplementation-during-winter-phe-and-nice-statement
17. Assessment of Urolithin A effects on muscle endurance, strength, inflammation, oxidative stress, and protein metabolism in male athletes with resistance training. Journal of the International Society of Sports Nutrition. 2024. https://www.tandfonline.com/doi/full/10.1080/15502783.2024.2419388
18. ClinicalTrials.gov. Effects of Mitopure (Urolithin A) on Skeletal Muscle Function, Iron Metabolism and Endurance Performance (ENDURO), NCT04783207. https://clinicaltrials.gov/study/NCT04783207
19. Mathews NM. Prohibited Contaminants in Dietary Supplements. Sports Health. 2018;10(1):19–30. https://pubmed.ncbi.nlm.nih.gov/28850291/

All product photography in this article is owned by Welzo and served from the Welzo media library. Research positions correct at the time of publication.