Caffeine
Also called: caffeine anhydrous, 1,3,7-trimethylxanthine, guarana, green tea extract (source of caffeine), pre-workout.
The best-documented stimulant in sport; the issue on store shelves is the dose per serving, stacking with coffee, and sleep.
What it is
Caffeine blocks adenosine receptors and reduces perceived exertion. The ISSN (International Society of Sports Nutrition) describes it as ergogenic in most trials, especially in endurance, in trained and untrained people alike. More than 95% is metabolized by the CYP1A2 enzyme, whose activity varies with your genes. People buy it in capsules, in pre-workouts, as gum and in energy drinks.
What the label does not say
- The trial dose is relative to body weight: 3 to 6 mg/kg (ISSN), or 210 to 420 mg for 70 kg; the minimum effective dose could be as low as 2 mg/kg, and at 9 mg/kg adverse effects are common with no additional gain. A fixed serving does not account for body weight.
- Pre-workouts concentrate the day into one serving: 254 ± 80 mg on average across 100 products analyzed (Jagim 2019), so a share of them exceeds 300 mg. Health Canada sets a natural health product at 200 mg per dose and 400 mg per day for regular use; between 400 and 1,000 mg per day, the monograph imposes "for occasional use only", a contraindication in case of hypertension or glaucoma and the requirement to avoid any other source of caffeine. Your morning coffee counts toward the total.
- The half-life is 4 to 6 hours (ISSN). A meta-analysis of 24 studies reports 45 minutes less total sleep and sleep efficiency reduced by 7 points, and calculates that a 217.5 mg dose (a typical pre-workout) should be taken at least 13.2 hours before bedtime, a 107 mg coffee at least 8.8 hours before. A late-afternoon workout with a pre-workout falls inside that window.
- Slow metabolizers exist: in the Guest trial (2018) cited by the ISSN, 4 mg/kg improved a 10 km cycling time trial by 6.8% in CYP1A2 AA genotypes, but worsened it by 13.7% in CC genotypes; at 2 mg/kg, no effect in CC. Without a genetic test, your individual response cannot be read on the label.
The forms on the shelf
- Anhydrous (capsule, powder): the form used in the vast majority of trials, because the dose is exact.
- Coffee: ergogenic too, but the ISSN reports 8- to 9-fold differences between coffees bought from comparable shops; the salivary peak arrives in 42 minutes with coffee versus 67 minutes with the capsule in a trial cited by the ISSN.
- Chewing gum, gels, mouth rinse: partly absorbed through the oral mucosa, shorter lead time before exercise according to the ISSN. Guarana, green tea and yerba mate in pre-workouts: caffeine under another name, which adds to the declared caffeine.
Published reference values
- Health Canada (foods): maximum 400 mg per day in healthy adults, 300 mg in case of pregnancy, breastfeeding or planning a pregnancy, 2.5 mg/kg in children and adolescents. Effects reported above that: insomnia, irritability, headaches, nervousness.
- ISSN: most reported side effects, tachycardia and palpitations, anxiety, headaches, insomnia, increasing with the dose. Tolerance: no consistent difference in effect between habitual and non-habitual consumers, contradictory results.
- Anti-doping: caffeine is not banned by the World Anti-Doping Agency but appears on its Monitoring Program, which tracks non-prohibited substances to detect patterns of misuse (USADA). The ISSN cites a reference threshold of 12 µg/mL of urine and a banning threshold of 15 µg/mL at the NCAA.
When
About 60 minutes before exercise in the trials, the plasma peak falling between 30 and 120 minutes; earlier with coffee, later with gum. Past early afternoon, the question is no longer performance but sleep.
Keep apart from
- Other sources of caffeine (coffee, tea, energy drinks, guarana): to be added into the daily total rather than spaced apart; Health Canada asks you to avoid them with a product at 400 mg per day, and 3 to 4 hours between two doses when the total exceeds 200 mg.
- Sedatives, synephrine, ephedrine: the Health Canada monograph rules out these combinations.
To mention to a professional
- Hypertension or glaucoma (advice required from 100 mg per day, contraindication above 400 mg according to Health Canada), chest pain or irregular heartbeat on caffeine (stop and consult), anxiety or sleep disorder, pregnancy, breastfeeding or planning a pregnancy: check with a health care professional.
From the plate first
According to Health Canada: drip coffee 179 mg per 237 mL, brewed coffee 135 mg, black or green tea 30 to 50 mg per 237 mL, cola 36 to 46 mg per 355 mL.
Sources
- Guest et al., ISSN position stand: caffeine and exercise performance, JISSN 2021
- Health Canada, Caffeine in Foods
- Health Canada, natural health product monograph, Caffeine
- Jagim et al., Common Ingredient Profiles of Multi-Ingredient Pre-Workout Supplements, Nutrients 2019
- Gardiner et al., The effect of caffeine on subsequent sleep: A systematic review and meta-analysis, Sleep Medicine Reviews 2023
- USADA, Substance Profile: Caffeine
- NIH Office of Dietary Supplements, Dietary Supplements for Exercise and Athletic Performance (Health Professional)
Educational information, drawn from the sources above. It does not replace the advice of a health professional, who remains the reference for your situation, your medications, pregnancy or breastfeeding.