Caffeine

Caffeine: How it works

• Caffeine is a central nervous stimulant, found in over 60 plants like coffee beans, tea leaves, cola nuts, and cocoa pods.

• Mechanisms of action:

  • Acts via adenosine blockade, releasing neurotransmitters like dopamine, catecholamines, and acetylcholine.

  • Enhances muscle contraction through increased calcium output from the sarcoplasmic reticulum.

  • Inhibits phosphodiesterases, reducing cAMP degradation, stimulating lipolysis, and activating the adrenaline cascade.

What is it used for?

• Improves aerobic performance with effects like increased heart rates, higher blood lactate levels, and elevated catecholamine levels.

• Enhances vigilance, alertness, mood, cognitive processes, and exercise performance (even with lower doses).

Evidence for or against its use

• A 2020 meta-analysis showed caffeine improves exercise performance across multiple tasks, with effects on muscle strength, anaerobic power, and aerobic endurance.

• Randomized studies confirmed improvements in neuromuscular efficiency, fatigue, and anaerobic performance without affecting EMG activity.

Safety concerns, side effects, and precautions

• High doses may cause gastrointestinal upset, nervousness, confusion, difficulty focusing, and disturbed sleep.

• Acute toxic levels (~10 g of caffeine or ~100 cups of coffee) can lead to fatal outcomes, especially when combined with stimulants or alcohol.

Interactions with other medications

• Caffeine is metabolized by the enzyme P450 1A2.

• Inhibitors of this enzyme (e.g., fluvoxamine, clozapine, mexiletine, enoxacin) can increase caffeine toxicity risk.

Key Web Sources

• Spriet LL. Exercise and sport performance with low doses of caffeine. Sports Med (Auckland).

  2014;44(Suppl 2):175–84. https://doi.org/10.1007/s40279-014-0257-8.

• Grgic J, Grgic I, Pickering C, Schoenfeld BJ, Bishop DJ, Pedisic Z. Wake up and smell

  the coffee: caffeine supplementation and exercise performance-an umbrella review of 21

  published meta-analyses. Br J Sports Med. 2020;54(11):681–8. https://doi.org/10.1136/

  bjsports-2018-100278.

• Saunders B, Oliveira LF, Silva RP, et al. Placebo in sports nutrition: a proof-of-principle

  study involving caffeine supplementation. Scand J Med Sci Sports. 2017;27(11):1240–7.

• San Juan AF, López-Samanes Á, Jodra P, et al. Caffeine supplementation improves anaerobic

  performance and neuromuscular efficiency and fatigue in olympic-level boxers. Nutrients.

  2019;11(9):2120. https://doi.org/10.3390/nu11092120.

• Greden JF. Anxiety or caffeinism: a diagnostic dilemma. Am J Psychiatry.

  1974;131(10):1089–92.

• Carrillo JA, Benitez J. Clinically significant pharmacokinetic interactions between dietary

  caffeine and medications. Clin Pharmacokinet. 2000;39(2):127–53.