Caffeine
Strong EvidenceThe world's most popular stimulant — proven ergogenic aid.
Not medical advice
Nutripedia summarises published peer-reviewed research. This content is for informational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare professional before taking any supplement.
Caffeine is a methylxanthine central nervous system stimulant that acts primarily by blocking adenosine receptors, reducing perceived effort and fatigue. It is one of the most studied ergogenic aids in sports science, with a consistent evidence base spanning endurance performance, strength, anaerobic power, reaction time, and alertness. EFSA has established 400 mg/day as the safe habitual intake for adults and has authorised a health claim for caffeine and endurance performance at 3 mg/kg. NHS guidance limits intake to 200 mg/day during pregnancy.
Robust umbrella review evidence (21 meta-analyses) for endurance, strength, and cognitive performance improvement. EFSA-authorised health claim for endurance performance at 3 mg/kg. EFSA safety reference dose: 400 mg/day adults, 200 mg/day in pregnancy. Sleep disruption at doses within 6 hours of bedtime is well-documented in RCTs.
Endurance Performance
21 studies · 1,512 participants
Alertness, Reaction Time & Cognitive Performance
25 studies · 2,100 participants
Sleep Quality (Adverse Effect)
15 studies · 980 participants
The Evidence
14 peer-reviewed papers, updated 3 weeks ago
8 meta-analyses · 2 systematic reviews · 1 RCT · 2 position stands · 1 regulatory document
Effects of Different Doses of Caffeine on Cognitive Performance in Healthy Physically Active Individuals
Ramírez-delaCruz M, Esteban-García P, Abián P et al.
European Journal of Nutrition
Reaction time improved only at 6 mg/kg caffeine vs placebo in physically active adults. Sustained attention, anticipation, and memory were unaffected at either dose. The 6 mg/kg dose also increased the incidence of side effects, suggesting a narrow benefit-to-risk window for high-dose cognitive use.
The Effect of Caffeine Supplementation on Muscular Strength and Endurance: A Meta-Analysis of Meta-Analyses
Taghizadeh Bilondi H, Valipour H, Khoshro S et al.
Heliyon
Synthesis of 9 meta-analyses confirmed caffeine supplementation significantly increases muscle strength (SMD=0.18, p<0.001) and muscle endurance (SMD=0.30, p<0.001). Authors note a gap in research specifically examining female athletes and hormonal influences on outcomes.
Effect of Caffeine Ingestion on Time Trial Performance in Cyclists: A Systematic Review and Meta-Analysis
Chen B, Ding L, Qin Q et al.
Journal of the International Society of Sports Nutrition
Moderate caffeine doses (4–6 mg/kg) significantly improved cycling time-trial performance in terms of both completion time and power output. Low doses (1–3 mg/kg) produced non-significant effects, identifying 4–6 mg/kg as the optimal ergogenic range for cyclists.
Caffeine Intake and Anxiety: A Meta-Analysis
Liu C, Wang L, Zhang C et al.
Frontiers in Psychology
Across 14 studies (546 participants) caffeine elevated anxiety risk in a dose-dependent manner. Lower doses produced modest increases; intake exceeding 400 mg/day resulted in substantially higher anxiety risk. Individuals with anxiety sensitivity may be particularly susceptible.
Moderators of Caffeine's Effects on Jumping Performance in Females: A Systematic Review and Meta-Analysis
Grgic J, Varovic D
Journal of the American Nutrition Association
Caffeine ingestion produced a significant ergogenic effect on vertical jumping performance in females (g=0.28) across 15 studies. Performance gains were notably larger during the follicular phase of the menstrual cycle, highlighting hormonal modulation of caffeine's ergogenic response.
International Society of Sports Nutrition Position Stand: Coffee and Sports Performance
Higgins S, Straight CR, Lewis RD et al.
Journal of the International Society of Sports Nutrition
Coffee is a complex matrix with neuromuscular, antioxidant, metabolic and cognitive effects relevant to sport. Its ergogenic impact varies by serving size, bean type, and brew method. Caffeine from coffee confers similar performance benefits to caffeine anhydrous.
The Effect of Caffeine on Subsequent Sleep: A Systematic Review and Meta-Analysis
Gardiner C, Weakley J, Burke LM et al.
Sleep Medicine Reviews
Caffeine reduced total sleep time by ~45 minutes and sleep efficiency by ~7%, and increased sleep onset latency by ~9 minutes. Coffee should be avoided ≥8.8 hours before bed; pre-workout supplements ≥13.2 hours before bed to minimise sleep disruption.
Effects of Caffeine Intake on Endurance Running Performance and Time to Exhaustion: A Systematic Review and Meta-Analysis
Wang Z, Qiu B, Gao J et al.
Nutrients
Analysis of 21 RCTs (254 participants) found caffeine produced a medium ergogenic effect on time-to-exhaustion running and a smaller improvement in time-trial completion time at doses of 3–9 mg/kg. Benefits were consistent across recreational and trained runners.
Does Acute Caffeine Supplementation Improve Physical Performance in Female Team-Sport Athletes? Evidence from a Systematic Review and Meta-Analysis
Gomez-Bruton A, Marin-Puyalto J, Muñiz-Pardos B et al.
Nutrients
Caffeine improved specific team-sport skills, countermovement jump, and grip strength in female athletes but showed no significant effect on agility, sprint ability, or perceived exertion. Findings support selective use of caffeine supplementation in female team-sport contexts.
The Neurophysiology of Caffeine as a Central Nervous System Stimulant and the Resultant Effects on Cognitive Function
Fiani B, Zhu L, Musch BL et al.
Cureus
Caffeine blocks adenosine A1 and A2A receptors, indirectly elevating dopamine, norepinephrine, and acetylcholine. This mechanism improves processing speed and memory in adults and older populations but evidence on attention is mixed and effects in children appear negative.
Caffeine and Cognitive Functions in Sports: A Systematic Review and Meta-Analysis
Lorenzo Calvo J, Fei X, Domínguez R et al.
Nutrients
Low-to-moderate caffeine doses before or during exercise significantly improved attention, accuracy, and simple reaction time in athletes. Benefits to memory and complex cognition were less consistent. Self-reported energy and mood also improved across included studies.
International Society of Sports Nutrition Position Stand: Caffeine and Exercise Performance
Guest NS, VanDusseldorp TA, Nelson MT et al.
Journal of the International Society of Sports Nutrition
Caffeine at 3–6 mg/kg body mass consistently improves aerobic endurance, muscular endurance, strength, sprint, and power output in trained and untrained individuals. Effects are modulated by genetics, habitual intake, and delivery method. Optimal timing is ~60 min pre-exercise.
Wake Up and Smell the Coffee: Caffeine Supplementation and Exercise Performance — an Umbrella Review of 21 Published Meta-Analyses
Grgic J, Grgic I, Pickering C et al.
British Journal of Sports Medicine
Across 21 meta-analyses, caffeine consistently improved aerobic endurance, muscle strength, muscle endurance, jumping, and power output. Effect magnitudes are generally larger for aerobic than anaerobic exercise. Most evidence is from young males, limiting broader generalisability.
Scientific Opinion on the Safety of Caffeine
EFSA Panel on Dietetic Products, Nutrition and Allergies (NDA)
EFSA Journal
Single caffeine doses up to 200 mg (≈3 mg/kg for a 70 kg adult) do not raise safety concerns. Habitual intake up to 400 mg/day is safe for non-pregnant healthy adults. Pregnant women should limit intake to 200 mg/day from all sources.
Evidence Database
Click any row to explore the studies behind each health outcome. Grades reflect the volume and quality of published research, not a recommendation.
| Grade | Health Outcome | |
|---|---|---|
| A | Endurance Performance21 studies | |
| A | Alertness, Reaction Time & Cognitive Performance25 studies | |
| A | Sleep Quality (Adverse Effect)15 studies | |
| B | Strength & Power Output18 studies | |
| C | Fat Oxidation9 studies |
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General Information
Dosage (Evidence-Reported)
These figures reflect what clinical studies used — not personalised recommendations.
Safety Notes
- Disrupts sleep: 400 mg taken 6 hours before bedtime reduced sleep time by ~1 hour in RCT
- Anxiety and jitteriness commonly reported above 3–6 mg/kg in trial participants
- NHS recommends maximum 200 mg/day during pregnancy
- Tolerance and physiological dependence develop with habitual use; withdrawal causes headache and fatigue
- Avoid combining with other stimulant ingredients (e.g. synephrine) — additive adverse effects
- EFSA caution for children/adolescents: limit 3 mg/kg/day
Key Benefits
- Consistently improves endurance time-trial performance (~2–4% across meta-analyses)
- EFSA-authorised health claim for caffeine and endurance performance
- Reduces reaction time and improves sustained attention — robust RCT evidence
- Modest improvements in upper and lower body strength (SMD 0.15–0.20)
- Increases fat oxidation during exercise — potential glycogen-sparing effect
Quick Facts
Legal food supplement (UK). EFSA-authorised health claim for increased endurance performance at 3 mg/kg body weight. EFSA daily reference dose 400 mg for adults. NHS advises limiting to 200 mg/day during pregnancy. Not a controlled substance.
Frequently Asked Questions
Nutripedia is an educational resource. Content is sourced from peer-reviewed studies and does not constitute medical advice. Consult a healthcare professional before starting any supplement.