Caffeine has been getting plenty of praise lately — based on scientific studies. Still, it often raises concerns: many of us grew up hearing that drinking too much coffee is harmful. The first study proving caffeine’s positive effect on performance (specifically in sports, during aerobic exercise) was published in 1978. Since then, caffeine has been studied extensively. It’s not entirely clear whether caffeine alone or its metabolites are responsible for its effects, but the benefits are well-documented.
A major sports physiology study by Wilmore & Costill (2001) confirmed several effects of caffeine, including:
- increased mental alertness;
- improved concentration;
- enhanced mood;
- reduced fatigue and delayed onset of tiredness;
- stimulation of catecholamine release (adrenaline, dopamine, etc.);
- mobilization of free fatty acids (boosting fat oxidation);
- increased use of muscle triglycerides (energy source for exercise);
- diuretic effect;
- improved calcium metabolism and sodium-potassium pump activity, which can enhance muscle performance in sprinters and strength athletes.
Caffeine’s positive effects on the nervous system (better mood, learning ability, memory, attention, productivity) are observed at 1–5 mg per kg of body weight. For reference: one espresso contains ~100 mg caffeine; coffee brewed in a cezve or moka pot has 90–200 mg. Effects are stronger in people who don’t consume caffeine regularly. Arnaud (2009) also found that caffeine’s benefits are diminished when taken with sugar — so tea and coffee are best consumed unsweetened.
When caffeine is harmful
At 9–13 mg per kg (roughly 6–9 shots of espresso for an average adult), caffeine causes negative effects: shorter and poorer sleep quality.
At 15 mg/kg, symptoms may include rapid heartbeat, headaches, nervousness, insomnia, irritability, and digestive issues. These occur with chronic overconsumption or abrupt withdrawal.
The lethal dose is more than 18 g per day (about 2 liters of espresso).
Some people experience insomnia, jitters, or anxiety even at moderate doses if they’re unaccustomed or particularly sensitive.
Caffeine content in drinks and foods:
- 90–200 mg — espresso/americano
- 2–3 mg — decaf coffee
- 70–80 mg — latte/cappuccino
- 40–100 mg — instant coffee
- 100 mg — cup of cocoa
- 40–50 mg — black tea
- 20–30 mg — green tea
- ~80 mg — 100 g chocolate
- 65 mg — 1 L Coca-Cola
- 100–350 mg — 1 L energy drink
