Cafeína
Also known as: Caffeine, 1,3,7-trimethylxanthine, guaranine, theine, methyltheobromine
Overview
Caffeine is a natural alkaloid found in various plants like coffee beans, tea leaves, and cacao pods. It functions as a central nervous system stimulant, primarily used to enhance alertness, reduce fatigue, and improve both physical and cognitive performance. Widely consumed in beverages and dietary supplements, caffeine is recognized for its psychoactive effects, increasing wakefulness and decreasing perceived exertion during exercise. Research on caffeine is extensive, with numerous high-quality randomized controlled trials, systematic reviews, and meta-analyses consistently supporting its ergogenic (performance-enhancing) effects, making it one of the most well-studied supplements.
Benefits
Caffeine offers several evidence-based benefits, particularly in athletic performance. A meta-analysis of randomized controlled trials demonstrated that caffeine significantly increases time to exhaustion in running tests with a medium effect size (Hedge’s g = 0.392) and reduces time to complete endurance running trials with a small effect size (g = -0.101). For strength and power, a systematic review and meta-analysis of 26 RCTs found small but significant improvements in handgrip strength (effect size = 0.28) and total throws in judo fitness tests (effect size = 0.42). Beyond physical performance, caffeine also improves cognitive function, alertness, and reduces the perception of effort during exercise. These ergogenic effects are observed in both recreational and trained athletes, though evidence for women is less conclusive and requires further research. The benefits are acute, typically manifesting 30-60 minutes after ingestion and lasting several hours.
How it works
Caffeine primarily exerts its effects by acting as an adenosine receptor antagonist, specifically blocking A1 and A2A receptors. By doing so, it counteracts adenosine's natural inhibitory effects on the central nervous system, leading to increased neuronal firing and the release of stimulating neurotransmitters such as dopamine and norepinephrine. This mechanism results in enhanced central nervous system stimulation, increased catecholamine release, and improved muscle contractility. Caffeine may also increase fat oxidation during exercise. It is rapidly absorbed in the gastrointestinal tract, reaching peak plasma concentrations within 30-60 minutes, with nearly 100% bioavailability.
Side effects
Caffeine is generally safe at moderate doses, typically up to 400 mg/day for healthy adults. However, it can cause several side effects. Common side effects, affecting more than 5% of users, include insomnia, jitteriness, increased heart rate, and gastrointestinal discomfort. Less common side effects (1-5%) can include anxiety, headache, and palpitations. Rarely, individuals may experience more severe effects such as arrhythmias, severe anxiety, or panic attacks, particularly at higher doses or in sensitive individuals. Caffeine can interact with certain medications metabolized by the CYP1A2 enzyme and may potentiate the effects of other stimulants. It is contraindicated or should be used with caution in individuals with cardiovascular disease, anxiety disorders, during pregnancy, and in those with certain psychiatric conditions. Pregnant individuals are advised to limit intake to approximately 200 mg/day, and children and adolescents are generally more sensitive to its effects.
Dosage
For ergogenic effects, a minimum effective dose of approximately 2 mg/kg body weight is suggested. The optimal dosage range commonly used in studies showing performance benefits is 3-6 mg/kg body weight, typically ingested 30-60 minutes prior to exercise for peak effect. The maximum safe dose for healthy adults is generally considered to be up to 400 mg/day; exceeding this increases the risk of adverse side effects. Caffeine is available in various forms, including anhydrous powder, capsules, and naturally in beverages like coffee and tea. While food intake may delay absorption, a fasting state generally leads to a faster onset of effects. No specific cofactors are required for its efficacy, though hydration status can influence tolerance.
FAQs
Is caffeine safe for daily use?
Yes, for most healthy adults, daily caffeine intake within recommended doses (up to 400 mg/day) is generally considered safe and well-tolerated.
Does caffeine cause dehydration?
No, current evidence does not support the notion that moderate caffeine consumption causes dehydration, even during exercise. It contributes to daily fluid intake.
Can caffeine cause dependence?
Regular, high-dose caffeine use can lead to mild physical dependence, and cessation may result in withdrawal symptoms like headaches, fatigue, and irritability.
Is caffeine effective for all types of exercise?
Caffeine shows the strongest evidence for improving endurance and strength-related activities. Its effects on other specific exercise types may vary and are less consistently demonstrated.
Are there differences between caffeine sources?
When matched for dose, pure caffeine (anhydrous) and caffeine from natural sources like coffee or tea have similar ergogenic effects and mechanisms of action.
Research Sources
- https://pubmed.ncbi.nlm.nih.gov/36615805/ – This meta-analysis by Grgic et al. (2023) analyzed multiple randomized controlled trials and found that caffeine significantly increased time to exhaustion in running tests with a medium effect size (g=0.392) and reduced time trial completion time with a small effect size (g=-0.101), confirming its ergogenic benefit in endurance running. The study noted limitations regarding fewer studies on women and optimal dosing strategies.
- https://pubmed.ncbi.nlm.nih.gov/35889953/ – Del Coso et al. (2022) conducted a systematic review and meta-analysis of 26 RCTs, revealing small but significant improvements in handgrip strength and judo-specific performance metrics following caffeine supplementation. The research was methodologically robust, though it highlighted heterogeneity in dosing and timing protocols across studies.
- https://www.tandfonline.com/doi/full/10.1080/15502783.2024.2323919 – This source, likely a review or position stand, supports caffeine's role as a central nervous system stimulant that improves alertness and physical performance. It emphasizes consistent findings across diverse populations and exercise modalities, reinforcing the high quality of evidence for caffeine's efficacy as an ergogenic aid.
