Table of Contents
The sports supplement industry generates billions of dollars annually, with countless products promising to unlock your endurance potential. The reality? About 90% of what's sold has little to no evidence of effectiveness. Of the remaining 10%, many work only in specific contexts or for certain athlete populations.
This guide separates the science from the marketing. We'll cover what the research actually shows—good and bad—for each supplement commonly used by runners, cyclists, triathletes, and other endurance athletes. No affiliate links, no sponsored content, just evidence.
Important caveat: Supplements are called "supplements" for a reason. They supplement an already solid foundation of training, nutrition, sleep, and recovery. No pill or powder will compensate for poor fundamentals. If you're not already training consistently, eating well, and sleeping adequately, start there.
1. Evidence Tiers: How We Rate Supplements
Tier 1: Strong Evidence
Multiple high-quality studies showing consistent benefits. Well-understood mechanisms. Established dosing protocols. These work for most athletes when used correctly.
Tier 2: Moderate Evidence
Some supporting research but with caveats. May work for certain populations, exercise types, or conditions. Benefits may be small or inconsistent across studies.
Tier 3: Limited Evidence
Insufficient research, mixed results, or only theoretical benefits. May work, but we can't say confidently. Often overhyped relative to actual evidence.
Our Evaluation Criteria
- Quality of studies: Randomized controlled trials > observational studies > anecdotes
- Replication: Multiple studies showing similar effects > single breakthrough study
- Effect size: Meaningful performance improvements > statistically significant but tiny effects
- Real-world relevance: Effects in trained athletes > effects in untrained subjects
- Safety profile: Well-studied safety data > limited safety research
2. Tier 1: Strong Evidence (They Work)
Caffeine
The most well-researched ergogenic aid in sports
How It Works
- • Blocks adenosine receptors (reduces fatigue perception)
- • Increases adrenaline release
- • Improves muscle contraction
- • Enhances fat oxidation
- • Reduces perceived effort (RPE)
Performance Benefits
- • Endurance: 2-4% improvement
- • Time trials: 1-3% improvement
- • High-intensity: 3-7% improvement
- • RPE: 5-6% reduction
Optimal Dosing Protocol
Dose
3-6mg per kg body weight
(210-420mg for 70kg athlete)
Timing
30-60 min before exercise
(Peak plasma: 45-90 min)
Sources
Coffee, caffeine pills, gels
(Pills most precise)
Pro Tips
- • Caffeine withdrawal protocol: Reduce intake 5-7 days before key races to restore sensitivity
- • Genetic variation: CYP1A2 gene affects metabolism; slow metabolizers may not benefit as much
- • Late-race dosing: A caffeine boost at mile 20 of a marathon can help (test in training)
- • More isn't better: Above 6mg/kg increases side effects without additional benefit
Beetroot Juice / Dietary Nitrates
Natural performance enhancer with solid evidence
How It Works
- • Nitrate → Nitrite → Nitric Oxide (NO)
- • NO causes vasodilation (blood vessel widening)
- • Improves oxygen delivery efficiency
- • Reduces oxygen cost of exercise
- • Enhances mitochondrial function
Performance Benefits
- • Time to exhaustion: 4-25% improvement
- • Time trials: 1-3% improvement
- • Oxygen efficiency: 3-5% improvement
- • Best for: Recreational athletes
Optimal Dosing Protocol
Dose
300-600mg nitrate
(~500ml beet juice or 1-2 shots)
Timing
2-3 hours before exercise
(Or daily for 3-7 days)
Sources
Beet juice, concentrated shots
(Beet It, SuperBeets, etc.)
Critical Warning
Do NOT use antibacterial mouthwash before taking beetroot juice. Oral bacteria are essential for converting nitrate to nitrite—mouthwash kills them and blocks the conversion pathway.
Sodium Bicarbonate (Baking Soda)
Buffer for high-intensity efforts
How It Works
- • Increases blood pH (more alkaline)
- • Buffers hydrogen ions from lactate
- • Delays acidosis in working muscles
- • Allows higher intensity before burnout
Performance Benefits
- • High-intensity (1-7 min): 2-3% improvement
- • Repeated sprints: 8% improvement
- • Best for: 1-10 minute max efforts
- • Less effective for: Pure endurance
Optimal Dosing Protocol
Dose
0.2-0.3g per kg body weight
(14-21g for 70kg athlete)
Timing
60-150 min before exercise
(Split into smaller doses)
Key Tip
Take with small carb meal
(Reduces GI distress)
GI Warning
Sodium bicarbonate can cause significant GI distress (bloating, cramping, diarrhea) in many athletes. Always trial in training first. Consider sodium citrate as an alternative if GI issues persist—it's gentler with similar effects.
Beta-Alanine
Intramuscular buffer for sustained high-intensity
How It Works
- • Increases muscle carnosine levels
- • Carnosine buffers H+ ions in muscle
- • Requires chronic loading (weeks)
- • Effects are cumulative, not acute
Performance Benefits
- • 30 sec - 10 min efforts: 2-3% improvement
- • Repeated sprints: Improved performance
- • Endurance: Limited direct benefit
- • May help: End-of-race kicks
Optimal Dosing Protocol
Dose
3.2-6.4g daily
(Split into 0.8-1.6g doses)
Loading Period
4-10 weeks minimum
(Carnosine builds slowly)
Maintenance
Continue daily dosing
(Effects reverse if stopped)
The Tingle
Beta-alanine causes paresthesia (tingling sensation) in many users, especially at higher single doses. This is harmless but can be uncomfortable. Splitting into smaller doses (0.8g every 3-4 hours) minimizes this effect. Sustained-release formulas also help.
3. Tier 2: Moderate Evidence (Situational)
💪 Creatine Monohydrate
What the research shows:
- • Excellent for power/strength (well-established)
- • Limited benefits for pure endurance
- • May help with sprint finishes, hill attacks
- • Improves recovery and training quality
- • Cognitive benefits (especially sleep-deprived)
Protocol:
- • Dose: 3-5g daily (skip loading)
- • Timing: Any time, with food
- • Form: Monohydrate (most researched)
- • Consideration: 2-4 lb water weight gain
Best for: Runners/cyclists doing mixed training, master's athletes, or those with high-intensity efforts in races.
🩸 Iron
What the research shows:
- • Critical if deficient (common in endurance athletes)
- • No benefit if levels are adequate
- • Female athletes, vegetarians at higher risk
- • Foot strike hemolysis depletes stores
Protocol (if needed):
- • Dose: Per physician guidance
- • Target ferritin: 35-50+ ng/mL for athletes
- • Take with: Vitamin C (enhances absorption)
- • Avoid with: Calcium, coffee, tea
Warning: Always test before supplementing. Excess iron is harmful. Get serum ferritin, iron, and transferrin saturation tested.
☀️ Vitamin D
What the research shows:
- • Essential for bone health (stress fracture prevention)
- • Immune function support
- • May improve muscle function if deficient
- • ~50% of athletes are insufficient
Protocol:
- • Target: 40-60 ng/mL (blood levels)
- • Typical dose: 1,000-5,000 IU daily
- • Form: D3 (cholecalciferol)
- • Take with: Fat (improves absorption)
Test first: Get 25(OH)D blood test. Dosing depends on current levels and sun exposure.
🍒 Tart Cherry Juice
What the research shows:
- • May reduce muscle soreness (DOMS)
- • Anti-inflammatory properties
- • May improve sleep quality
- • Recovery enhancement (not performance)
Protocol:
- • Dose: 8-12 oz twice daily
- • Timing: 4-5 days before/after hard events
- • Form: Juice concentrate or capsules
Caution: Like other antioxidants, chronic use may blunt training adaptations. Best reserved for competition/recovery periods.
4. Tier 3: Limited Evidence (Uncertain)
These supplements are often marketed to endurance athletes but have limited or inconsistent research supporting their use:
| Supplement | Claimed Benefits | Reality |
|---|---|---|
| BCAAs | Reduce fatigue, preserve muscle | Unnecessary if adequate protein intake; whole protein is superior |
| L-Carnitine | Fat burning, endurance | Body makes enough; supplementation rarely increases muscle levels |
| Glutamine | Immunity, recovery | Most goes to gut; limited evidence for athlete benefits |
| HMB | Muscle preservation | May help during extreme calorie deficits; limited endurance data |
| Cordyceps | Oxygen utilization | Mixed results; most positive studies in untrained/elderly |
| Rhodiola | Fatigue reduction, adaptation | Some anti-fatigue effects; inconsistent performance data |
| Quercetin | Mitochondrial biogenesis | Lab results don't translate to human performance |
| Collagen | Joint/tendon health | Emerging evidence for connective tissue; performance unproven |
The Bottom Line on Tier 3
These aren't necessarily harmful—they just don't have compelling evidence for endurance performance. If budget is limited, spend on Tier 1 supplements first. If you try Tier 3 supplements, be your own experiment: track performance objectively and be honest about whether you see real benefits.
5. Foundation Supplements (Health First)
Before chasing performance supplements, ensure your foundation is solid. These address common deficiencies and support overall health:
Daily Essentials
-
✓
Vitamin D3
1,000-5,000 IU daily (test first)
-
✓
Omega-3 Fish Oil
1-3g EPA+DHA daily for inflammation
-
✓
Magnesium
200-400mg (glycinate/citrate forms)
Test Before Supplementing
-
⚠️
Iron
Only if ferritin is low; excess is harmful
-
⚠️
B12
Especially for vegans/vegetarians
-
⚠️
Zinc
Often depleted in athletes; 15-30mg if deficient
6. Timing and Stacking Protocols
Race Day Protocol (Example)
Beetroot juice shot (300-600mg nitrate)
Allows time for nitrate conversion
Pre-race meal with sodium bicarbonate (if using)
Split bicarb dose with carbs to reduce GI issues
Caffeine (3-6mg/kg)
Peak effect during race
Additional caffeine via gels (optional)
For events over 90 minutes
Daily Training Protocol
Morning
- • Vitamin D3 with breakfast (fat-containing)
- • Fish oil with food
- • Creatine (3-5g) at any time
- • Beta-alanine dose 1 (0.8-1.6g)
Evening
- • Magnesium with dinner or before bed
- • Beta-alanine dose 2 (0.8-1.6g)
- • Tart cherry juice (if in heavy training block)
- • Iron if needed (away from calcium/coffee)
7. Safety and Third-Party Testing
The Contamination Problem
Studies consistently find that 10-25% of supplements contain banned substances not listed on the label. This is true even for "natural" products. For athletes subject to drug testing, this creates real doping violation risk.
Common contaminants: anabolic steroids, stimulants, SARMs, ephedra, prescription medications
Trusted Third-Party Certifications
NSF Certified for Sport
Gold standard; tests for 270+ banned substances
Informed Sport
Tests every batch; WADA-recognized
BSCG Certified
Drug-free certification; tests for 500+ substances
Red Flags to Avoid
- 🚩 "Proprietary blends" that hide actual ingredient amounts
- 🚩 Extreme claims ("10x your performance," "pharmaceutical-grade")
- 🚩 Before/after testimonials as primary evidence
- 🚩 No third-party testing or certifications listed
- 🚩 Manufactured overseas without quality verification
- 🚩 Price too good to be true (quality costs money)
8. What to Avoid
High-Dose Antioxidants During Heavy Training
Vitamin C (>500mg) and Vitamin E supplements taken during training may blunt adaptations. The oxidative stress from exercise is a training signal—blocking it can reduce mitochondrial improvements.
Better: Get antioxidants from whole foods. Save supplements for competition/recovery periods.
Unknown Pre-Workout Blends
Many pre-workouts contain untested combinations and often have undisclosed stimulants. The "kick" often comes from excessive caffeine or worse.
Better: Make your own: caffeine + beta-alanine (if desired). You know exactly what you're taking.
Fat Burners and Weight Loss Supplements
Most are either ineffective or potentially dangerous. The "thermogenic effect" is minimal and often comes from stimulants that tax your cardiovascular system.
Better: Calorie deficit through diet, strategic caffeine use, and more training.
Testosterone Boosters
Despite marketing claims, no legal supplement meaningfully increases testosterone in healthy young men. They're a waste of money and some contain hidden prohormones that could trigger doping violations.
Better: Prioritize sleep, manage stress, eat adequate fat and calories, and lift heavy things.
9. Frequently Asked Questions
What supplements actually work for endurance athletes?
The supplements with strong scientific evidence for endurance performance are caffeine (3-6mg/kg), beetroot juice/nitrates (300-600mg nitrate), sodium bicarbonate (0.2-0.3g/kg), and beta-alanine (3-6g daily for 4+ weeks). Creatine may help with high-intensity efforts within endurance events. Most other supplements lack sufficient evidence for endurance benefits.
How much caffeine should I take before a race?
Research supports 3-6mg per kg of body weight taken 30-60 minutes before exercise. For a 70kg athlete, that's 210-420mg of caffeine. Start with the lower end (3mg/kg) to assess tolerance. Higher doses don't provide additional benefits and increase side effects. Regular caffeine users may need to reduce intake for 5-7 days before competition to maximize effects.
Does beetroot juice really improve endurance performance?
Yes, beetroot juice has strong evidence for improving endurance performance by 1-3% through increased nitric oxide production, which improves oxygen efficiency. Take 300-600mg of dietary nitrate (about 500ml of beetroot juice) 2-3 hours before exercise. Effects are strongest in recreational athletes and diminish in highly trained elites. Avoid mouthwash before taking—it kills bacteria needed for nitrate conversion.
Should endurance athletes take creatine?
Creatine's benefits for pure endurance are limited, but it can help with sprint finishes, hill attacks, or any high-intensity efforts within endurance events. The 2-4 lb water weight gain may be a concern for weight-sensitive sports. For multi-sport athletes or those doing mixed training, 3-5g daily of creatine monohydrate is beneficial. Skip the loading phase—just take it daily.
Are there any supplements endurance athletes should avoid?
Avoid antioxidant megadoses (high-dose vitamin C/E) during heavy training—they may blunt training adaptations. Be cautious with pre-workouts containing unknown proprietary blends. Avoid supplements making extreme claims without research backing. Always check third-party testing (NSF Certified for Sport, Informed Sport) to avoid contamination and doping violations.
The Honest Bottom Line
Supplements are the smallest lever in endurance performance. Training, nutrition, sleep, and recovery all matter more. The best supplements might give you a 1-3% edge—meaningful in competition, but meaningless if your fundamentals are lacking.
Start with the proven basics: caffeine for races, maybe beetroot juice if you tolerate it, and ensure you're not deficient in key nutrients. Everything else is optional optimizing that should only happen after your training and lifestyle are dialed in.
No supplement will make you an athlete. Consistent, smart training does that. Supplements just help you express the fitness you've already earned.
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