Caffeine

Popularity

  • World’s most widely consumed pharmacologically active substance (Pesta 2013)

Caffeine in Food and Drinks

  • Coffee
  • Tea
  • Energy drinks and bars
  • Chocolate

Mechanism of Action

  • A central nervous system stimulant of the methylxanthine class (Pesta 2013)
  • Blocks adenosine (Pesta 2013) 
    • Prevents the onset of drowsiness
    • Can decrease cerebral blood flow
      • Decrease myocardial blood flow by reducing adenosine-mediated vasodilatation
  • Increased fatty acid oxidation (Pesta 2013) 
    • Increased lipolysis leads to decreased reliance on glycogen use
      • Increasing hormone sensitive lipase (HSL) activity
      • Decreases glycogen phosphorylase activity
  • Increases rates of postexercise muscle glycogen accumulation when ingested with carbohydrates after exercise-induced glycogen depletion (Pesta 2013)
  • Increases contractile force during submaximal contractions (Pesta 2013) 
    • Increases calcium release from the sarcoplasmic reticulum
    • Decrease calcium reuptake

Effect on Exercise and Rest

  • No change in cardiac output (ACSM 2013)
  • Heart rate
    • Increase in resting heart rate (ACSM 2013)
    • Increase or no change in heart rate during exercise (ACSM 2013)
  • Increase blood pressure during exercise (ACSM 2013)

Ergogenic Effect

  • Increases concentration and alertness (Pesta 2013)
  • Increases cognitive function and fine motor skills (Pesta 2013)
  • Increases athletic performance (Pesta 2013) 
    • Delays the onset of muscle fatigue and central fatigue (Pesta 2013)
    • Increased anaerobic sports performance (Pesta 2013)
      • No significant performance increases in a Wingate test in untrained subjects (Pesta 2013)
      • Counters reductions in maximum dynamic strength and muscle power output on the morning (2.5–7.0%) (Pesta 2013)
        • increases muscle performance to the levels found in the afternoon.
    • Increased aerobic sports performance (Pesta 2013)
      • Increase endurance (ACSM 2013)
      • 5 mg/kg can improve sprint performance cycling and running time trial performance endurance
    • Increased cycling power output

Ergolytic and Side Effects

  • Diuretic (Pesta 2013) 
    • Potential decrease of performance during prolonged endurance events
  • Restlessness (Pesta 2013)
  • Tremors (Pesta 2013)
  • Tachycardia (Pesta 2013)

Medical Benefits

  • Possible protective effect against Parkinson's disease (Pesta 2013)
  • Possible protective effect from liver cirrhosis (Pesta 2013)
  • May decrease severity of acute mountain sickness (Pesta 2013) 
    • Must be taken a few hours prior to attaining a high altitude

Precautions

  • Possibly decreases calcium absorption (Jones & Barlett 2011)
  • Increases intraocular pressure in those with glaucoma (Pesta 2013) 
    • Does not affect normal individuals

Side Effects

  • Mild drug dependence (Pesta 2013)
  • Withdrawal symptoms include sleepiness, headache, and irritability (Pesta 2013)

Banned Status

  • Since 2004, caffeine has been removed from the WADA prohibited list (Pesta 2013)
  • Although now approved, WADAs continues to monitor caffeine levels to study potential misuse in sports (Pesta 2013)

Reference

American College of Sports Medicine (2013). Guidelines for Exercise Testing and Prescription, William & Wilkins, 9, 404

Bishop D (December 2010). "Dietary supplements and team-sport performance". Sports Medicine. 40(12): 995–1017.

Jones & Barlett (2011) Nurse's Handbook of Combination Drugs, Jones & Bartlett Publishers, 10th Edition. 170-171.

Pesta DH, Angadi SS, Burtscher M, Roberts CK (2013). "The effects of caffeine, nicotine, ethanol, and tetrahydrocannabinol on exercise performance". Nutrition & Metabolism. 10(1): 71.

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