The Endurance Supplement Reference
A no-hype guide to what works, what doesn't, and what depends.
Most supplement content for runners is written to sell. This one is written to sort.
Below is every supplement that has either a strong evidence base or a strong mechanism for endurance running, ranked by how much the research actually supports the use case. We name the doses. We name the studies. We name the trade-offs. Where the evidence is weak, we say so.
If you take only one thing from this page, most marketed "endurance stacks" contain three things that work, two things that work at higher doses than the label provides, and four things that don't work at all. Knowing which is which is the entire job.
The standard. Not the streak.
How to read this guide
For every compound below, we cover four things:
Mechanism. What it actually does in the body. Not the marketing claim. The biology.
Evidence tier. A — multiple randomized trials and meta-analyses in trained athletes. B — meaningful evidence but mixed or limited to specific populations. C — mechanistic plausibility, weak human data. D — popular but unsupported in endurance contexts.
Dose and timing. The dose that was actually used in the studies that worked. Not the dose on the average label.
Who should consider it. And, more importantly, who shouldn't bother.
This is the parent reference. Each compound links to a deeper file where we walk through the trials, the dosing math, and the practical protocols.
Tier A — Evidence is strong
These compounds have been studied in trained endurance athletes across multiple randomized trials with consistent direction of effect. They are the foundation.
Carbohydrate
The single most studied performance compound in endurance science. There is no debate about whether carbohydrates during exercise improves performance over distances longer than 90 minutes. The debate is only about dose ceiling.
For decades the guidance was 30–60 g/hour. Then 60–90 g/hour with multiple transportable carbohydrates (glucose plus fructose, typically 1:0.8 ratio). The current frontier is 90–120 g/hour for elite endurance athletes, validated in trained mountain marathoners (Viribay et al. 2020; Ravikanti et al. 2025).
For recreational and amateur runners, the floor matters more than the ceiling. Under-fueling is the dominant failure mode. Most marathoners take in 30–40 g/hour and bonk. Train the gut up. Practice 60 g/hour for a year. Move to 90 g/hour only when the gut tolerates it.
Dose: 60–90 g/hour for marathon; up to 120 g/hour for ultras in trained athletes.
Mapped to product: race-day fuel sits outside Dark Mile's catalog. Most readers will use a combination of gels, sports drinks, and real food.
Caffeine
The most consistently effective ergogenic aid in endurance sport. Meta-analyses across thousands of subjects show small but reliable performance improvements at 3–6 mg/kg taken 30–60 minutes before exercise (Grgic et al. 2019). For a 150 lb runner, that's roughly 200–400 mg.
Side effects are dose-dependent. GI distress, anxiety, and sleep disruption all climb past 6 mg/kg. Genetic variation in CYP1A2 changes the response. Some people are fast metabolizers and clear caffeine before it helps; others are slow metabolizers and feel jittery for hours.
Dose: 3–6 mg/kg, 30–60 minutes before the event. Roughly 200–400 mg for a 150 lb runner.
Not in the Dark Mile catalog. Pre-workout caffeine sources are widely available; whole-food coffee works equally well for most runners.
Beetroot (dietary nitrate)
Dietary nitrate converts to nitric oxide in the body, improving mitochondrial efficiency and reducing the oxygen cost of submaximal exercise. The evidence base is large. Meta-analyses confirm a small but real performance benefit in recreational and competitive athletes, with diminishing returns in elites (Senefeld et al. 2020; Zhang et al. 2025).
The optimal dose is 6–13 mmol of nitrate (roughly 370–810 mg), 90–180 minutes before exercise, ideally with 3–7 days of pre-loading. Capsule and powder forms work if the nitrate content is standardized. Most marketed beetroot products are underdosed.
Dose: 6–13 mmol nitrate (370–810 mg), 2–3 hours pre-exercise.
Beetroot Powder
Beetroot Capsules
Creatine monohydrate
The most-studied supplement in sports nutrition. Endurance runners have historically dismissed it because it doesn't directly lift VO2max. But the indirect benefits are real and well-documented: better recovery between hard sessions, lean mass retention during high-volume blocks, bone density support, and emerging evidence for cognitive function and brain energy metabolism (Kreider et al. 2017; Forbes et al. 2023).
The weight-gain concern is real but small. Most runners gain 2–4 lb of water weight in the first week. That weight is metabolically active and stabilizes within 4 weeks.
Dose: 3–5 g/day, no loading required.
Vitamin D + K2
Vitamin D is the bone, muscle, and immune nutrient. Deficiency is common in runners — especially northern-latitude, indoor-training, and dark-skinned runners. Stress fracture risk climbs sharply at serum 25(OH)D below 30 ng/mL (Lappe et al. 2008; Halliday et al. 2011).
K2 is the partner nutrient. Without K2, vitamin D drives calcium into circulation but not necessarily into bone. The MK-7 form of K2 has the longest half-life and best bioavailability.
Dose: 2,000–5,000 IU vitamin D3 daily; 100–200 mcg MK-7 K2 daily. Test serum 25(OH)D twice a year.
Bone & Heart Support (Vitamin K2 + D3)
Omega-3 (EPA + DHA)
The 2024 International Society of Sports Nutrition position on omega-3 fatty acids is the current authority. EPA and DHA reduce systemic inflammation, support cardiovascular health, and may attenuate exercise-induced muscle damage (ISSN 2024).
The catch: most fish oil supplements are oxidized before they reach the runner. A 2024 multi-year analysis of 72 products found that 68% of flavored omega-3 supplements exceeded the GOED industry rancidity limit of 26 TOTOX (Hands et al. 2024). Rancid fish oil is worse than no fish oil.
Dose: 2–3 g/day combined EPA + DHA
Tier B — Evidence is meaningful but mixed
These compounds have legitimate research support, but the effect is smaller, the protocol matters more, or the benefit is limited to specific populations or use cases.
Magnesium glycinate
The most commonly oversold supplement in the runner market. The pitch is that it prevents cramps. The evidence is that it does not (Garrison et al. 2020 Cochrane review).
What magnesium does support: sleep quality, neuromuscular relaxation, and overall recovery in runners who are deficient. Heavy sweaters and runners on high-carbohydrate diets are most at risk for low intake. Glycinate is the form with the best absorption-to-tolerance ratio. Oxide is about 4% absorbed and worth avoiding.
Dose: 200–400 mg elemental magnesium from glycinate or citrate, evening dosing.
CoQ10 / Ubiquinol
CoQ10 sits at the center of the mitochondrial electron transport chain. Endogenous production declines roughly 20% per decade past age 30. The 2024 systematic review of CoQ10 in athletes concluded that supplementation reduced markers of exercise-induced muscle damage and oxidative stress, with stronger effects in masters athletes (Sarmiento et al. 2025).
Dose: 100–300 mg ubiquinol daily with a fat-containing meal.
L-citrulline
Citrulline boosts nitric oxide more efficiently than arginine because it bypasses first-pass hepatic metabolism. The evidence for endurance performance is mixed. A 2022 meta-analysis found a small benefit for time-to-exhaustion protocols, but the effect on time-trial performance is unclear (d'Unienville et al. 2022).
The recovery case is stronger. Citrulline appears to reduce post-exercise soreness and improve subsequent-day performance in repeated efforts.
Dose: 6–8 g citrulline malate, 60 minutes before exercise.
Bovine colostrum
The trust case for colostrum is the runner's gut case. A 2024 meta-analysis of 10 randomized trials concluded that bovine colostrum significantly reduced intestinal permeability markers in athletes (Khoshbin et al. 2024). The lactulose/rhamnose ratio drops. Zonulin drops. The gut barrier strengthens.
Colostrum should not be sold as a protein supplement or a muscle-building agent. The IGF-1 in colostrum does not raise circulating IGF-1 in humans (Duff et al. 2019). It is a gut-barrier product. That is what the evidence supports.
Dose: 500 mg–25 g/day depending on use case. 500 mg twice daily is the validated leaky-gut protocol.
Iron (for at-risk runners only)
Iron deficiency is common in endurance runners, especially female runners, vegetarians, and high-mileage athletes in heavy training blocks. Hepcidin, an iron-regulating hormone, rises 3–6 hours after hard running and blocks absorption (Peeling et al. 2014).
Iron should not be supplemented blindly. Excess iron is pro-oxidant and pro-inflammatory. Test serum ferritin before starting. Target ferritin >40 ng/mL for trained endurance athletes. Dose iron in the morning, ideally with vitamin C, and not within 6 hours of a hard session.
Dose: 18–65 mg elemental iron, taken every other day, morning only. Test ferritin every 3–6 months.
Not currently in the Dark Mile catalog. We recommend testing first and working with a clinician.
Tier C — Mechanism is plausible, evidence is limited
These compounds have a defensible mechanism and some signal in the literature, but the trials are smaller, less consistent, or limited to non-running populations.
Shilajit
Himalayan resin is rich in fulvic acid and trace minerals. A 2019 randomized trial in adult men found that 500 mg/day of purified shilajit for 8 weeks attenuated muscle strength loss after repetitive exercise (Keller et al. 2019). The mechanism is plausibly mitochondrial; the trial population was small.
This is a product where we will tell you what the evidence shows and let you decide. We don't claim it's a proven performance enhancer. We claim it has signal worth watching for masters athletes and high-altitude trainees.
Dose: 250–500 mg purified shilajit daily.
Collagen + vitamin C (for tendons)
The Shaw and Baar 2017 protocol: 15 g gelatin or hydrolyzed collagen with 50 mg vitamin C, consumed 60 minutes before tendon-loading activity. In their study, this protocol doubled collagen synthesis markers in healthy adults.
The evidence base has grown. Connective tissue remodeling depends on amino acid availability during the loading window. For runners with chronic tendinopathies — Achilles, plantar, patellar — this is a low-risk intervention with mechanistic support.
Dose: 15 g hydrolyzed collagen + 50 mg vitamin C, 30–60 minutes before tendon-loading work.
Tier D — Popular but unsupported in endurance contexts
These compounds are sold heavily to runners. The evidence does not support the use case.
BCAAs
Branched-chain amino acids became popular in the 1990s as a recovery and anti-catabolic supplement. The Wolfe 2017 review summarizes the current scientific consensus: in athletes consuming adequate total dietary protein, BCAA supplementation provides no additional benefit. The marketing outran the biology.
If you eat 1.6 g/kg of protein per day (roughly 110 g for a 150 lb runner), BCAAs add nothing. We do not sell them.
Glutamine (as a muscle supplement)
Glutamine is conditionally essential. The body produces it in adequate quantities for most uses. The marketed claims around glutamine and muscle growth or recovery are not supported in healthy athletes (Gleeson 2008).
The use case where glutamine has signal is gut barrier health — specifically as part of a runner's gut protocol alongside colostrum. That is how Dark Mile positions L-Glutamine: as a gut-repair compound, not a muscle compound.
Dose: 5–10 g/day for gut barrier support.
Multivitamins (for trained athletes with adequate diets)
A high-quality whole-food diet typically meets micronutrient needs for most runners. The exceptions — iron, vitamin D, omega-3, sometimes B12 for vegetarians — are better addressed with targeted supplementation than with a broad multivitamin.
The case for a multivitamin is strongest in athletes with restricted diets, athletes traveling extensively, or athletes in heavy energy-restricted phases. Otherwise it is insurance you don't need.
Greens powders (as a vegetable replacement)
Greens powders are convenience products. They contain a fraction of the polyphenols, fiber, and bioavailable nutrients of the equivalent whole vegetables.
We sell Greens Superfood Powder. We sell it because it does provide a meaningful dose of micronutrients and polyphenols when whole vegetables are not available. We do not sell it as a replacement for vegetables. There is no replacement for vegetables.
How to actually build a stack
Most runners ask the wrong question. "What should I take?" is downstream of "what am I training for, what is my baseline, and where am I currently failing?"
Build from the bottom up.
Layer 1 — Diet and sleep. No supplement compensates for chronic under-fueling or 5 hours of sleep. Fix these first.
Layer 2 — Foundational health. Vitamin D, omega-3, and possibly magnesium. These address the most common deficiencies in runners. Test 25(OH)D and ferritin twice a year.
Layer 3 — Training support. Creatine for high-volume blocks. Beetroot in race build-up. Caffeine on hard sessions.
Layer 4 — Recovery and resilience. Colostrum for runners with chronic gut issues. CoQ10 for masters athletes. Collagen for runners with tendon history.
Layer 5 — Race day. Carbohydrate, sodium, and fluid. The most leveraged 4 hours of the year.
If you skip layers 1 and 2 to focus on layer 5, you will not run well. We see this constantly.
What we will not sell
We will not sell BCAAs. The evidence does not support the use case.
We will not sell a "fat burner." Body composition is downstream of training load and dietary discipline.
We will not sell a "testosterone booster." There is no over-the-counter ingredient that meaningfully changes serum testosterone in healthy adult men.
We will not sell a "pre-workout" with proprietary blends. Proprietary blends exist to hide under-dosing.
If we add a product, the dose will be on the label, the form will be the bioavailable one, and the evidence will be in the file.
The bottom line
Most runners need fewer supplements than they take and more discipline than they admit.
If you take vitamin D, omega-3, and creatine — and you eat real food, sleep 8 hours, and run consistently — you are doing more for your performance than 90% of the runners who own 15 bottles.
The work happens in the miles. The supplements support the work.
Built in the dark. Earn it.
References
Duff, W. R. D., et al. (2019). Oral bovine colostrum supplementation does not increase circulating IGF-1. Nutrition Research, 66, 68–78.
Forbes, S. C., et al. (2023). Effects of creatine supplementation on brain function and health. Nutrients, 15(4), 921.
Garrison, S. R., et al. (2020). Magnesium for skeletal muscle cramps. Cochrane Database of Systematic Reviews.
Gleeson, M. (2008). Dosing and efficacy of glutamine supplementation in human exercise and sport training. Journal of Nutrition, 138(10), 2045S–2049S.
Grgic, J., et al. (2019). Wake up and smell the coffee: caffeine supplementation and exercise performance — an umbrella review. British Journal of Sports Medicine, 54(11), 681–688.
Halliday, T. M., et al. (2011). Vitamin D status relative to diet, lifestyle, injury, and illness in college athletes. Medicine & Science in Sports & Exercise, 43(2), 335–343.
Hands, J. M., et al. (2024). A multi-year rancidity analysis of 72 marine and microalgal oil omega-3 supplements. Journal of Dietary Supplements, 21(2), 195–206.
ISSN (2024). International Society of Sports Nutrition position stand: long-chain omega-3 polyunsaturated fatty acids. Journal of the International Society of Sports Nutrition.
Keller, J. L., et al. (2019). The effects of Shilajit supplementation on fatigue-induced decreases in muscular strength. Journal of the International Society of Sports Nutrition, 16, 3.
Khoshbin, K., et al. (2024). Bovine colostrum in increased intestinal permeability in healthy athletes and patients: a meta-analysis. Digestive Diseases and Sciences, 69(4), 1345–1360.
Kreider, R. B., et al. (2017). International Society of Sports Nutrition position stand: safety and efficacy of creatine supplementation. Journal of the International Society of Sports Nutrition, 14, 18.
Lappe, J., et al. (2008). Calcium and vitamin D supplementation decreases incidence of stress fractures in female navy recruits. Journal of Bone and Mineral Research, 23(5), 741–749.
Peeling, P., et al. (2014). Iron status and the acute post-exercise hepcidin response in athletes. PLoS One, 9(3), e93002.
Ravikanti, et al. (2025). 13C labelled glucose-fructose shows greater exogenous and whole-body CHO oxidation at 120 vs 60 & 90 g/h. Journal of Applied Physiology.
Sarmiento, S., et al. (2025). Can CoQ10 supplementation reduce exercise-induced muscle damage and oxidative stress in athletes? A systematic review and meta-analysis.
Senefeld, J. W., et al. (2020). Ergogenic effect of nitrate supplementation: a systematic review and meta-analysis. Medicine & Science in Sports & Exercise, 52(10), 2250–2261.
Shaw, G., et al. (2017). Vitamin C-enriched gelatin supplementation before intermittent activity augments collagen synthesis. American Journal of Clinical Nutrition, 105(1), 136–143.
Viribay, A., et al. (2020). Effects of 120 g/h of carbohydrates intake during a mountain marathon on exercise-induced muscle damage in elite runners. Nutrients, 12(5), 1367.
Wolfe, R. R. (2017). Branched-chain amino acids and muscle protein synthesis in humans: myth or reality? Journal of the International Society of Sports Nutrition, 14, 30.
Zhang, J. Q., et al. (2025). Effects of beetroot juice on physical performance in professional athletes and healthy individuals: an umbrella review.
Last revision: May 2026.