Quick answer
- Only a handful of supplements have strong evidence for endurance running: caffeine in modest doses before hard efforts (published guidance starts around 3 mg per kilogram, and EFSA sets 200 mg in one dose and 400 mg a day as safe for healthy adults), dietary nitrate from beetroot juice two to three hours before, creatine monohydrate for the strength and repeated-effort side of training, sodium bicarbonate for events of one to ten minutes (only with advice from a professional, as it often upsets the stomach), and carbohydrate and electrolyte products used during exercise.
- Iron and vitamin D correct genuine deficiencies but do nothing if you are not deficient.
- Most other running supplements have weak evidence, and high-dose antioxidants can actively blunt training adaptation.
5 key facts
- The International Olympic Committee consensus identifies only a small group of supplements with sound evidence of performance benefit.
- Beetroot juice works through nitrate, so the dose is the nitrate content, not the bottle size; cooked or "sports" versions vary enormously.
- Creatine is not just a strength supplement; it supports repeated high-intensity efforts, strength work, and possibly glycogen storage.
- High-dose vitamin C and E during a training block has been shown to interfere with the endurance adaptations training is meant to produce.
- Supplements are not pre-approved by regulators, so athletes subject to anti-doping rules should buy only batch-tested products.
The supplement industry is very good at selling runners things. It is much less good at demonstrating that those things work. The useful way through this is the one national sports institutes use: grade everything by the strength of the evidence, be honest about how small the effects are, and remember that a supplement can only improve a foundation that already exists.
That last point deserves emphasis before any of the specifics. Nothing in this article will outperform sleeping properly, eating enough carbohydrate, or training consistently. Supplements are the last one percent, and they are worth exactly one percent. The amounts below are ranges from published guidance for healthy adults, not a prescription: talk to a doctor or registered dietitian before you start any supplement, especially if you take medicines or have a health condition.
Tier a: genuinely supported by evidence
Caffeine
Published guidance for healthy adultsAbout 3 mg/kg; at most 200 mg in one dose and 400 mg a day (EFSA)
When45 to 60 min before
Realistic benefitAmong the most reliable ergogenic aids in endurance sport; improves perceived effort and time to exhaustion
Dietary nitrate (beetroot)
Published guidance for healthy adultsAbout 5 to 9 mmol (310 to 560 mg) nitrate (IOC consensus)
When2 to 3 h before
Realistic benefitImproved running economy and time-trial performance, strongest in recreational rather than elite runners
Creatine monohydrate
Published guidance for healthy adults3 to 5 g daily (IOC consensus)
WhenAny time, daily
Realistic benefitStrength work, hill repeats, repeated efforts, and possibly glycogen storage
Sodium bicarbonate
Published guidance for healthy adultsOnly with advice from a sports doctor or dietitian
WhenBefore short races
Realistic benefitBuffers acidity in efforts of roughly 1 to 10 minutes; useful for 800 m to 3,000 m, not marathons. Often causes stomach trouble
Carbohydrate products
Published guidance for healthy adults30 to 90 g/hour
WhenDuring exercise over 60 to 90 min
Realistic benefitThe largest performance effect of anything on this page
Electrolyte and fluid products
Published guidance for healthy adultsIndividual
WhenDuring long or hot sessions
Realistic benefitMaintains fluid balance; not a performance drug in itself
| Supplement | Published guidance for healthy adults | When | Realistic benefit |
|---|---|---|---|
| Caffeine | About 3 mg/kg; at most 200 mg in one dose and 400 mg a day (EFSA) | 45 to 60 min before | Among the most reliable ergogenic aids in endurance sport; improves perceived effort and time to exhaustion |
| Dietary nitrate (beetroot) | About 5 to 9 mmol (310 to 560 mg) nitrate (IOC consensus) | 2 to 3 h before | Improved running economy and time-trial performance, strongest in recreational rather than elite runners |
| Creatine monohydrate | 3 to 5 g daily (IOC consensus) | Any time, daily | Strength work, hill repeats, repeated efforts, and possibly glycogen storage |
| Sodium bicarbonate | Only with advice from a sports doctor or dietitian | Before short races | Buffers acidity in efforts of roughly 1 to 10 minutes; useful for 800 m to 3,000 m, not marathons. Often causes stomach trouble |
| Carbohydrate products | 30 to 90 g/hour | During exercise over 60 to 90 min | The largest performance effect of anything on this page |
| Electrolyte and fluid products | Individual | During long or hot sessions | Maintains fluid balance; not a performance drug in itself |
Two of these deserve a closer look because runners get the practical details wrong.
Caffeine is dose-sensitive. Published guidance starts at about 3 mg per kilogram, and higher doses mostly add jitters, an elevated heart rate, and gut trouble. EFSA puts the safe limit for healthy adults at 200 mg in one dose and 400 mg in a day, so count coffee, gels and pre-race products together and stay under it. Habitual coffee drinkers still respond, so there is no need for a withdrawal period, though some runners prefer to reduce intake in the days before a key race so the dose feels larger. And it is a laxative for many people, which is a scheduling problem rather than a pharmacological one.
Beetroot juice works because of nitrate, which the body converts to nitrite and then nitric oxide, improving the oxygen cost of running. The dose that matters is nitrate content, usually expressed in millimoles or milligrams, and it varies wildly between products. Concentrated "shot" formats are standardised; a supermarket carton often is not. Effects are largest in recreationally trained runners and smaller in highly trained athletes, and an important practical detail is that antibacterial mouthwash blocks the oral bacteria that make the conversion possible. Do not rinse with mouthwash on race morning if you are relying on beetroot.
Tier B: correct a deficiency, do nothing otherwise
Iron
When it helpsDiagnosed iron deficiency, with or without anaemia; more common in female runners and in high-mileage athletes
When it does nothingNormal ferritin. Excess iron is harmful; never supplement without a blood test
Vitamin D
When it helpsLow blood levels, common at high latitudes in winter and in indoor-heavy athletes
When it does nothingAdequate status. More is not better
Calcium
When it helpsLow dietary intake, particularly with dairy avoidance or bone stress injury history
When it does nothingA normal diet including dairy or fortified alternatives
Vitamin B12
When it helpsVegan or vegetarian diets
When it does nothingOmnivorous diets
Magnesium
When it helpsGenuinely low intake
When it does nothingAlmost all runners. Despite the marketing, magnesium supplementation does not reliably prevent cramp
| Supplement | When it helps | When it does nothing |
|---|---|---|
| Iron | Diagnosed iron deficiency, with or without anaemia; more common in female runners and in high-mileage athletes | Normal ferritin. Excess iron is harmful; never supplement without a blood test |
| Vitamin D | Low blood levels, common at high latitudes in winter and in indoor-heavy athletes | Adequate status. More is not better |
| Calcium | Low dietary intake, particularly with dairy avoidance or bone stress injury history | A normal diet including dairy or fortified alternatives |
| Vitamin B12 | Vegan or vegetarian diets | Omnivorous diets |
| Magnesium | Genuinely low intake | Almost all runners. Despite the marketing, magnesium supplementation does not reliably prevent cramp |
Iron is the one worth being deliberate about, especially for female runners and anyone training at high volume, because deficiency produces exactly the symptoms runners blame on overtraining: heavy legs, high heart rate at easy pace, and stalled progress. It is also the one that is genuinely harmful to take unnecessarily. Get a ferritin test, treat what the test shows, and retest.
Tier C: situational, modest, or still unclear
Beta-alanine
The claimBuffers acidity in short hard efforts
The honest state of the evidenceReal but small, and only for efforts of roughly 1 to 4 minutes. Requires weeks of loading and causes harmless tingling
Collagen or gelatin with vitamin C
The claimTendon and ligament support
The honest state of the evidencePromising early evidence when taken about an hour before loading. Not a protein source
Tart cherry juice
The claimReduces muscle soreness and speeds recovery
The honest state of the evidenceSome supportive data for recovery between close-together efforts; may blunt adaptation if used constantly
Probiotics
The claimFewer gut problems and infections
The honest state of the evidenceMixed. Some evidence for reduced upper respiratory illness and gut symptoms; strain-specific and inconsistent
Ketone esters
The claimAlternative fuel and improved recovery
The honest state of the evidenceInconsistent performance results, expensive, and frequently causes gut distress
Nitric oxide "pump" products
The claimVasodilation and endurance
The honest state of the evidenceIf it does not contain a real nitrate dose, it is beetroot marketing without beetroot
| Supplement | The claim | The honest state of the evidence |
|---|---|---|
| Beta-alanine | Buffers acidity in short hard efforts | Real but small, and only for efforts of roughly 1 to 4 minutes. Requires weeks of loading and causes harmless tingling |
| Collagen or gelatin with vitamin C | Tendon and ligament support | Promising early evidence when taken about an hour before loading. Not a protein source |
| Tart cherry juice | Reduces muscle soreness and speeds recovery | Some supportive data for recovery between close-together efforts; may blunt adaptation if used constantly |
| Probiotics | Fewer gut problems and infections | Mixed. Some evidence for reduced upper respiratory illness and gut symptoms; strain-specific and inconsistent |
| Ketone esters | Alternative fuel and improved recovery | Inconsistent performance results, expensive, and frequently causes gut distress |
| Nitric oxide "pump" products | Vasodilation and endurance | If it does not contain a real nitrate dose, it is beetroot marketing without beetroot |
Tier D: skip these
- BCAAs and EAAs alongside adequate protein. If you already eat 1.6 g per kg of complete protein, added branched-chain amino acids add cost and nothing measurable.
- Glutamine for immunity or recovery in healthy athletes. Repeatedly tested, repeatedly unimpressive.
- High-dose antioxidant vitamins C and E taken daily through a training block. This is the important one: reactive oxygen species are part of the signal that drives endurance adaptation, and high-dose supplementation has been shown to interfere with those adaptations. Eat fruit and vegetables; do not megadose.
- Fat burners and thermogenics. Ineffective at best, and several have been withdrawn for safety reasons.
- Collagen sold as a runner’s protein powder. It is an incomplete protein and cannot count toward your daily protein target.
- Anything promising to replace carbohydrate during long runs. There is no such product.
Contamination is a real, boring risk
Dietary supplements are not approved by regulators before sale in most markets, and independent screening programmes have repeatedly found products containing substances not listed on the label, including anabolic agents and stimulants. For a recreational runner that is a health issue. For anyone competing in a federation with anti-doping rules, including many age-group championships and qualifying events, it is a sanction risk, and strict liability means "it was in my protein powder" is not a defence.
- Buy only products carrying Informed Sport or NSF Certified for Sport batch testing if you are subject to testing.
- Be most careful with pre-workouts, fat burners, and anything marketed for muscle building, which is where contamination is most often found.
- Prefer single-ingredient products. A proprietary blend of 22 ingredients is 22 chances to be surprised.
- Check that a product’s dose matches the studied dose. Many contain a fraction of what the research used, at full price.
A sensible stack for a marathon runner
If you want the short version, this is what a defensible plan looks like for a healthy runner training for a marathon.
Every day
Nothing, unless a blood test says otherwise. Creatine at 3 to 5 g if you also lift
Winter at high latitude
Vitamin D, at a dose guided by a blood test
During long runs and races
Carbohydrate at 30 to 90 g per hour, plus fluid and sodium matched to sweat losses
Before key sessions and races
Caffeine at about 3 mg/kg (at most 200 mg in one dose), rehearsed in training first
Optional, before a goal race
Nitrate 2 to 3 hours before, if tested in training
Never
Anything new on race day
| Context | What to take |
|---|---|
| Every day | Nothing, unless a blood test says otherwise. Creatine at 3 to 5 g if you also lift |
| Winter at high latitude | Vitamin D, at a dose guided by a blood test |
| During long runs and races | Carbohydrate at 30 to 90 g per hour, plus fluid and sodium matched to sweat losses |
| Before key sessions and races | Caffeine at about 3 mg/kg (at most 200 mg in one dose), rehearsed in training first |
| Optional, before a goal race | Nitrate 2 to 3 hours before, if tested in training |
| Never | Anything new on race day |
That is a short list, and it should be. The runners who improve most from a nutrition change are almost never the ones who added a supplement. They are the ones who started eating enough carbohydrate on their hard days.
Frequently asked questions
What supplements should runners take?
For most healthy runners: caffeine before key efforts, carbohydrate and electrolytes during long sessions, and creatine if you also strength train. Iron and vitamin D only when a blood test shows a deficiency. Everything else is optional and small.
Does beetroot juice really improve running performance?
Yes, modestly, through its nitrate content. Take roughly 400 to 800 mg of nitrate about two to three hours before an event, and avoid antibacterial mouthwash, which blocks the oral bacteria needed to convert it. Effects are larger in recreational runners than in highly trained ones.
Should runners take magnesium for cramp?
Probably not. Despite heavy marketing, magnesium supplementation has not reliably reduced exercise-associated muscle cramp in trials. Cramping is more strongly associated with neuromuscular fatigue and unaccustomed intensity than with mineral status.
Do runners need iron supplements?
Only if a blood test shows low ferritin. Iron deficiency is genuinely common in runners, particularly female runners and high-mileage athletes, and it causes fatigue and elevated heart rate at easy paces. Taking iron without a deficiency is unhelpful and potentially harmful.
Is creatine useful for endurance runners?
Yes, more than its reputation suggests. It supports strength training, hill repeats, and repeated high-intensity efforts, and may help glycogen storage. It causes a small increase in body water, which some runners dislike near a goal race.
Can antioxidant supplements hurt my training?
High doses can. Daily high-dose vitamin C and E during a training block has been shown to interfere with the cellular signalling that produces endurance adaptations. Get antioxidants from food and skip the megadoses.
Sources
- 1IOC Consensus Statement: Dietary Supplements and the High-Performance AthleteBritish Journal of Sports Medicine (Maughan et al., 2018)The evidence grading behind the tiers used here, plus contamination risk
- 2International Society of Sports Nutrition Position Stand: Caffeine and Exercise PerformanceJISSN (Guest et al., 2021)Caffeine dosing, timing, and habituation
- 3Dietary Nitrate Supplementation and Exercise PerformanceSports Medicine (Jones, 2014)Nitrate dose, timing, and the mouthwash interaction
- 4Vitamin C and E Supplementation Hampers Cellular Adaptation to Endurance Training in HumansJournal of Physiology (Paulsen et al., 2014)Why high-dose antioxidants can blunt training adaptation
- 5International Society of Sports Nutrition Position Stand: Creatine Supplementation and ExerciseJISSN (Kreider et al., 2017)Creatine dosing and its effects beyond pure strength sport
General guidance for healthy adults, not medical advice. Talk to a doctor or registered dietitian if you have a health condition, take medicines or have special dietary needs. Caffeine advice is for healthy adults only. EFSA's safe limit is 200 mg in one dose and 400 mg in a day.
