Caffeine

Regulatory note: Caffeine in food and dietary supplements is subject to specific labelling requirements in the EU. Beverages containing ≥150 mg/L caffeine must carry the statement “High caffeine content. Not recommended for children or pregnant or breastfeeding women.” The following is a summary of published research and does not constitute a health claim under Regulation (EC) No 1924/2006.

What is Caffeine?

Caffeine (chemical name: 1,3,7-trimethylxanthine) is a xanthine alkaloid found naturally in coffee beans, tea leaves, cacao, guarana, and yerba maté. It is the most widely consumed psychoactive substance in the world — billions of people ingest caffeine in some form every day.

In supplement form, caffeine anhydrous is used: a white crystalline powder with a standardised caffeine content, free from the accompanying compounds found in natural sources.

Mechanism: Adenosine Receptor Antagonism

Caffeine’s primary mechanism is competitive inhibition of adenosine receptors (predominantly A1 and A2A) in the central nervous system.

Adenosine is the brain’s sleep-pressure signal: it accumulates during waking hours, binds to receptors, and progressively induces drowsiness. Caffeine blocks these receptors without degrading or generating adenosine itself — temporarily suppressing the subjective sensation of fatigue without resolving the underlying sleep debt.

Additional mechanisms:

• Adrenaline release: Caffeine indirectly stimulates the adrenal medulla, producing a mild sympathomimetic response.
• Dopaminergic effects: Caffeine increases dopamine availability in specific brain regions (reward circuitry), which may contribute to its mood-enhancing properties.
• Muscular effects: Caffeine enhances calcium release from the sarcoplasmic reticulum in muscle cells, improving contractile force output.
• Fat mobilisation: Caffeine increases lipolysis via adrenaline-mediated pathways — an effect that attenuates substantially with habitual use.

What the Evidence Actually Shows

Well-established (hundreds of RCTs, multiple meta-analyses)

• Alertness, vigilance, and reaction time: Caffeine reliably reduces subjective sleepiness and improves vigilance in controlled studies — most pronounced under sleep deprivation or during extended shifts. A systematic review by McLellan et al. (2016) covering >120 studies found consistent benefits across military and occupational populations.
• Endurance performance: Meta-analyses report consistent improvements in running, cycling, and rowing tasks (~1–4% time trial improvement; SMD ~0.3–0.4). A 2020 meta-analysis by Grgic et al. (>300 studies) confirms endurance as the most robustly affected domain.
• Strength and power output: Moderate effects on maximal strength and sprint power; more consistent for upper-body exercises. Effect sizes are smaller than for endurance (SMD ~0.2–0.3).
• Cognition: Improved processing speed, working memory, and sustained attention — more pronounced under fatigue or sleep restriction. Benefits in fully rested individuals are smaller.

Well-studied, but with important caveats

• Tolerance development: With daily use, tolerance to alertness effects develops within days to weeks as adenosine receptor density upregulates. Endurance performance benefits appear more resistant to tolerance than wakefulness effects — but the evidence base here is less definitive.
• Weight management: Caffeine modestly increases energy expenditure (roughly 3–4% in acute studies) and fat oxidation rate. Long-term effects on body weight are minimal and tolerance-dependent; caffeine is not a meaningful fat-loss intervention on its own.
• Mood: Small to moderate improvements in mood and well-being in experimental settings; at high doses, anxiety and dysphoria can emerge instead.

Limitations and open questions

• Long-term effects of high-dose caffeine anhydrous on cardiac rhythm, blood pressure, and sleep architecture remain incompletely characterised.
• Epidemiological benefits associated with habitual coffee consumption (reduced diabetes risk, lower all-cause mortality) cannot be attributed to caffeine alone. Coffee contains hundreds of bioactive compounds — chlorogenic acids, diterpenes, trigonelline — that likely contribute independently.
• Most performance trials use doses of 3–6 mg/kg body weight in trained athletes. Effects in untrained populations or at lower doses are more variable.

Dosing

• Typical supplement dose: 100–200 mg, taken 30–60 minutes before exercise or cognitively demanding tasks.
• Endurance performance (evidence-based): 3–6 mg/kg body weight ~60 minutes before exercise. At 70 kg body weight, this corresponds to ~210–420 mg.
• EFSA safety threshold: Single doses up to 200 mg are considered safe; 400 mg/day from all sources is the recommended maximum for healthy adults.
• Pregnant women: Maximum 200 mg/day from all sources combined (coffee, tea, chocolate, supplements).
• Timing: Half-life is 3–5 hours in most adults (up to 9–10 hours in some individuals). Consumption after 2–3 pm may impair sleep quality.

Caffeine Sources — Reference Table

Tolerance and Dependence

Regular caffeine use leads to tolerance: adenosine receptor density increases (upregulation), so the same dose produces weaker effects over time. This explains why habitual coffee drinkers experience far less stimulation than occasional users from an identical dose.

Withdrawal after sustained intake (≥200 mg/day for several weeks) typically produces:

• Headaches (most common symptom)
• Fatigue and lethargy
• Difficulty concentrating
• Low mood

Symptoms typically resolve within 2–9 days. Caffeine dependence does not meet psychiatric criteria for addiction but does fulfil criteria for tolerance and withdrawal. The DSM-5 lists caffeine withdrawal as a diagnosable condition.

Interactions

• Adenosine analogues / cardiac medications: Caffeine antagonises adenosine effects and may interfere with diagnostic adenosine infusions used in cardiac stress testing.
• Ephedrine / synephrine: Combining caffeine with adrenergic stimulants significantly increases cardiovascular risk; such combinations in supplements are broadly prohibited in the EU.
• Anticoagulants (warfarin): Very high caffeine doses may affect pharmacokinetics; clinically relevant interactions are uncommon.
• Other stimulants (L-tyrosine, guarana): Additive effects — track total daily caffeine from all sources.
• Alcohol: Caffeine reduces subjective sleepiness without reversing alcohol’s objective impairment of motor coordination — a potentially dangerous dissociation.

Safety

Caffeine in moderate amounts is considered likely safe and well-tolerated in healthy adults. The EFSA safety opinion (2015) provides clear risk thresholds:

• Up to 400 mg/day (healthy adults): no identified health risk.
• Up to 200 mg per single dose: safe before physical exertion.
• Pregnant and breastfeeding women: max. 200 mg/day from all sources.
• Children and adolescents: EFSA recommends a maximum of 3 mg/kg body weight/day.

Adverse effects at excessive doses:

• Tachycardia and cardiac arrhythmias
• Elevated blood pressure in susceptible individuals
• Insomnia and disrupted sleep architecture
• Anxiety, nervousness, tremor
• Gastrointestinal discomfort (gastric acid stimulation)

Use with caution in:

• Cardiac arrhythmias or coronary artery disease
• Hypertension
• Pregnancy
• Anxiety disorders
• Chronic insomnia

Regulatory Status in Germany and the EU

• Caffeine is not a novel food in the EU and may be used in food products and dietary supplements.
• Mandatory labelling: Beverages with ≥150 mg/L caffeine must carry the warning “High caffeine content. Not recommended for children or pregnant or breastfeeding women (X mg caffeine/100 ml).”
• Health claims: Despite positive EFSA scientific opinions on alertness and endurance performance (2011), no caffeine health claims have been added to the EU authorised list (Annex of Regulation (EU) No 432/2012).
• Pure caffeine powder: Highly concentrated caffeine anhydrous products (e.g. bulk powder) have faced additional restrictions in several EU member states due to overdose risks; in Germany, the LFGB (Food and Feed Code) governs safe dosing requirements.

Conclusion

Caffeine is the most thoroughly researched ergogenic supplement available and delivers reliable, reproducible effects on alertness, endurance performance, and short-term cognitive function at moderate doses. Effects on wakefulness are substantially reduced with habitual use due to tolerance; periodic abstinence or cyclical use can restore sensitivity. For general longevity purposes, caffeine is less relevant than for acute performance optimisation. The 400 mg/day safety threshold should be respected; sensitive groups — pregnant women, individuals with cardiac conditions, children — require lower limits.