Only a handful of supplements reliably help runners, cyclists and triathletes: caffeine, carbohydrate products, and in some cases dietary nitrate. Iron and vitamin D help only when you are low, and a blood test should decide that. Most other products have weak or early evidence. If you are drug-tested, every supplement also carries a small risk of contamination with banned substances.
How we graded these supplements
Our backbone is the IOC consensus statement on dietary supplements, written by more than 20 sports nutrition and anti-doping experts (Maughan et al., 2018). It concluded that only a few performance supplements have good evidence. Those are caffeine, creatine, nitrate, sodium bicarbonate and possibly beta-alanine. It also stressed that food comes first, and that any supplement should be trialled in training before racing.
The letter grades below are ours, not the IOC's. They describe the evidence for endurance athletes specifically.
- A: strong evidence of a performance benefit in endurance events when used correctly.
- B: useful in specific situations, or when a deficiency is confirmed.
- C: mixed, early or indirect evidence.
- D: little evidence for endurance athletes, or possible harm.
| Supplement | Grade | Best evidence-based use |
|---|---|---|
| Caffeine | A | 3–6 mg/kg about 60 minutes before, or 100–300 mg during long efforts |
| Carbohydrate products (drinks, gels, chews) | A | 30–60 g per hour, up to 90 g per hour in events over 2.5 hours |
| Dietary nitrate (beetroot) | B | Recreational athletes; small effect, weaker in highly trained |
| Sodium / electrolytes | B | Replacing large sweat losses in ultra-endurance events |
| Protein powder | B | Convenience when food cannot meet daily needs |
| Iron | A if deficient, D if not | Only after blood tests and with clinical follow-up |
| Vitamin D | B if low | Depends on sun exposure and skin type; test first |
| Creatine | C | Sprint and strength work; weight gain may hurt endurance |
| Olive polyphenols | C | Early human data on oxidative stress markers; no performance data |
| Curcumin, tart cherry | C | Soreness markers; IOC says more research is needed |
| High-dose vitamins C and E | D | May blunt training adaptations |
Caffeine: grade A
Caffeine is the best-supported performance aid for endurance work. The IOC lists 3–6 mg per kg of body mass about 60 minutes before exercise (Maughan et al., 2018). Lower doses of 100–300 mg taken during endurance exercise may improve cycling time-trial performance by 3–7%.
The ISSN position stand reached a similar view. It found aerobic endurance shows the most consistent moderate-to-large benefits from caffeine (Guest et al., 2021). More is not better. The IOC notes that side effects become more common at 9 mg/kg or more. Test your dose in training, and watch sleep after late sessions.
Carbohydrate products: grade A
Sports drinks, gels and chews are the most useful "supplements" most endurance athletes will ever buy. They are simply a convenient way to eat carbohydrate while moving. Guidelines suggest 30–60 g per hour for longer events, and up to 90 g per hour for events beyond 2.5 hours (Burke et al., 2011). The higher rates need blends of different sugars, such as glucose and fructose, to be absorbed well.
A typical gel sachet holds about 25 g of carbohydrate, according to the IOC's product table. Practise your race fuelling in training so your gut adapts.
Beetroot and nitrate: grade B
Dietary nitrate raises nitric oxide availability. The IOC protocol is 5–9 mmol (310–560 mg) of nitrate, taken 2–3 hours before exercise (Maughan et al., 2018). Studies have linked it to 1–3% better time-trial performance in efforts under 40 minutes.
The catch is who benefits. A meta-analysis of 80 studies found a small overall effect (Senefeld et al., 2020). No benefit was seen in well-trained endurance athletes with a VO2max of 65 mL/kg/min or more. No benefit was seen in the six studies that included only women. For a deeper look, read our article on beetroot nitrates and olive polyphenols.
Sodium and electrolytes: grade B
The IOC lists electrolyte products for replacing large sodium losses during ultra-endurance activity. Typical products contain 50–60 mmol/L of sodium. Heavy, salty sweaters in long, hot events gain the most. For a one-hour run, ordinary meals usually cover sodium. Electrolytes do not make overdrinking safe, so drink sensibly.
Protein: grade B
Most runners can meet protein needs from food. The ISSN suggests 1.4–2.0 g per kg per day for exercising people, spread as 20–40 g doses every 3–4 hours (Jäger et al., 2017). A powder is useful when travel or appetite makes that hard. The IOC warns that some protein products contain extra ingredients that raise the risk of contamination.
Iron: grade A if deficient, D if not
Iron deficiency is common in endurance sport. A review estimated it affects about 15–35% of female athlete groups and 5–11% of male athlete groups (Sim et al., 2019). Low iron can impair training and performance.
Do not take iron blind. The IOC recommends blood tests such as serum ferritin and haemoglobin to stage any deficiency. Athletes who are deficient need clinical follow-up, which may include higher-dose iron. Unneeded iron can cause stomach upset and, rarely, harmful overload.
Vitamin D: grade B if low
The IOC notes that many athletes risk low vitamin D at some point in the year. The IOC notes that deficiency can affect bone health. The need to supplement depends on sun exposure and skin type, so a blood test is the sensible first step.
Creatine: grade C for endurance
Creatine has strong evidence for repeated sprints and strength work. The IOC lists a maintenance dose of 3–5 g per day. For distance runners, there is a trade-off. The IOC notes a likely 1–2 kg gain in body mass, mostly water, which may hurt endurance performance. It can still suit gym blocks or sprint-finish events.
Olive polyphenols: grade C
We make an olive polyphenol product, so we hold this grade to a strict standard. A 2025 scoping review found only seven studies on olive-derived polyphenols and exercise-induced inflammation (Lillis et al., 2025). Most tested hydroxytyrosol, at an average of about 101 mg per day for about 40 days. The authors found limited agreement in human studies.
One randomised trial gave 29 recreationally active adults an olive fruit water extract or placebo for 16 days (Roberts et al., 2022). It found modest changes in some antioxidant markers after exercise, but not in others. It did not measure race performance. That is early, indirect evidence. It is not a reason to expect a faster marathon.
The EU allows one specific claim: olive oil polyphenols contribute to the protection of blood lipids from oxidative stress. The effect is obtained with a daily intake of 20 g of olive oil containing at least 5 mg of hydroxytyrosol and its derivatives. That claim is about blood lipids, not performance.
Antioxidants, curcumin and tart cherry: grades C to D
The IOC reviewed curcumin and tart cherry juice and said more research is needed before recommending them for soreness. It also warned that high doses of single antioxidants, particularly vitamins C and E, may blunt training adaptations. That warning concerns high-dose single nutrients, not antioxidant-rich foods.
Supplements for drug-tested athletes: what should you check?
Under anti-doping rules, athletes are strictly liable for anything in their sample. Contamination is a real risk. In an international study, 94 of 634 supplements (14.8%) contained anabolic steroids not declared on the label (Geyer et al., 2004).
Third-party testing programs exist to help manage that risk:
- Informed Sport, run by LGC, tests every batch of a certified product for banned substances before release.
- NSF Certified for Sport, from NSF, lets athletes search certified products by name or lot number.
- BSCG (Banned Substances Control Group) runs a Certified Drug Free program and a searchable client database.
The IOC is clear that no scheme can guarantee a product is entirely safe. These programs reduce risk rather than remove it. Check that the exact product and batch you hold is listed. Ask your governing body which programs it recognises.
For transparency: Phenolia has been screened for banned substances by LGC, but final certification has not yet been issued. Two capsules provide 12 mg of olive polyphenols. That is well below the roughly 101 mg daily average in the studies Lillis reviewed. You can read what is in Phenolia before deciding.
What should a runner actually take?
- Get the basics right first: enough total food, carbohydrate around training and sleep.
- Get blood tests for iron and vitamin D if you train hard, especially if you are female or vegetarian.
- Use carbohydrate products and caffeine for long sessions and races, practised in training.
- Consider beetroot if you are recreationally trained and race shorter, intense events.
- If you are tested, use only batch-tested products, and keep records.
For the wider picture of food and recovery, see our pillar on olive oil for athletic performance and recovery and olive oil for triathletes.
Sources
- Maughan RJ, Burke LM, Dvorak J, et al. IOC consensus statement: dietary supplements and the high-performance athlete. British Journal of Sports Medicine. 2018;52(7):439–455. doi.org/10.1136/bjsports-2018-099027
- Guest NS, VanDusseldorp TA, Nelson MT, et al. International society of sports nutrition position stand: caffeine and exercise performance. Journal of the International Society of Sports Nutrition. 2021;18(1):1. doi.org/10.1186/s12970-020-00383-4
- Burke LM, Hawley JA, Wong SH, Jeukendrup AE. Carbohydrates for training and competition. Journal of Sports Sciences. 2011;29(Suppl 1):S17–S27. doi.org/10.1080/02640414.2011.585473
- Senefeld JW, Wiggins CC, Regimbal RJ, et al. Ergogenic effect of nitrate supplementation: a systematic review and meta-analysis. Medicine & Science in Sports & Exercise. 2020;52(10):2250–2261. doi.org/10.1249/MSS.0000000000002363
- Jäger R, Kerksick CM, Campbell BI, et al. International Society of Sports Nutrition Position Stand: protein and exercise. Journal of the International Society of Sports Nutrition. 2017;14:20. doi.org/10.1186/s12970-017-0177-8
- Sim M, Garvican-Lewis LA, Cox GR, et al. Iron considerations for the athlete: a narrative review. European Journal of Applied Physiology. 2019;119(7):1463–1478. doi.org/10.1007/s00421-019-04157-y
- Lillis JB, Willmott AGB, Chichger H, Roberts JD. The application of olive-derived polyphenols on exercise-induced inflammation: a scoping review. Nutrients. 2025;17(2):223. doi.org/10.3390/nu17020223
- Roberts JD, Lillis JB, Pinto JM, et al. The impact of a natural olive-derived phytocomplex (OliPhenolia) on exercise-induced oxidative stress in healthy adults. Nutrients. 2022;14(23):5156. doi.org/10.3390/nu14235156
- Geyer H, Parr MK, Mareck U, et al. Analysis of non-hormonal nutritional supplements for anabolic-androgenic steroids: results of an international study. International Journal of Sports Medicine. 2004;25(2):124–129. doi.org/10.1055/s-2004-819955
- European Commission. Commission Regulation (EU) No 432/2012 establishing a list of permitted health claims. 2012. eur-lex.europa.eu
