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Caffeine: The Ups and Downs of Consumption

Caffeine: The Ups and Downs of Consumption

From your morning cup of coffee, to your evening Jägerbomb, caffeine is everywhere and is the most commonly used drug in the entire world. Research has shown that if taken in moderation, caffeine can have a multitude of health benefits.

Occurring naturally in some foods but primarily added artificially to consumer items such as energy drinks and medicines such as Anadin. Typically paired with pain relieving medicines in order to counteract the drowsiness that typically comes with them, caffeine is typically used to improve alertness with an upper limit of around 400mg per day maximum, 400mg is the equivalent of approximately 2-3 cups of coffee depending on strength. Although you can order decaffeinated coffee, be aware that there are still trace amounts of it in the drink and caution should be taken in regards to certain health conditions such as allergies/ heart conditions etc.


The mechanisms of caffeine

A study published in 1992 by Nehlig, Daval and Debry elaborates on the mechanisms of caffeine and the nervous system:

“Mobilization of intracellular calcium and inhibition of specific phosphodiesterases only occur at high non-physiological concentrations of caffeine. The only likely mechanism of action of the methylxanthine is the antagonism at the level of adenosine receptors. Caffeine increases energy metabolism throughout the brain but decreases at the same time cerebral blood flow, inducing a relative brain hypoperfusion. Caffeine activates noradrenaline neurons and seems to affect the local release of dopamine. Many of the alerting effects of caffeine may be related to the action of the methylxanthine on serotonin neurons.” (Nehlig, Daval, & Debry, 1992)

Caffeine stimulates the central nervous system (CNS), heightening alertness, and sometimes causing restlessness and agitation. It relaxes smooth muscle, stimulates the contraction of cardiac muscle, and enhances athletic performance. Furthermore, it promotes gastric acid secretion and increases gastrointestinal motility. It is often combined in products with analgesics and ergot alkaloids, relieving the symptoms of migraine and other types of headaches. Finally, caffeine acts as a mild diuretic.

Caffeine mechanisms in the CNS

Caffeine interacts with numerous systems within the human body some of which are as follows:

  • Respiratory system– Respiratory center stimulation in the central nervous system, a reduced threshold to hypercapnia with increased response, and increased consumption of oxygen, among others.
  • Central nervous system– Caffeine demonstrates antagonism of all 4 adenosine receptor subtypes (A1, A2a, A2b, A3) in the central nervous system.
  • Renal system– Caffeine has diuretic properties due its effects on renal blood flow
  • Cardiovascular system– Due to adenosine receptor antagonism, catecholamine release is triggered causing stimulatory effects in the heart and across the body.

Although contrary to popular belief, caffeine has been deemed a non-addictive substance, as research has shown that it does not activate the neural pathways linked to addiction, that being said, caffeine withdrawal was added to the list of recognized conditions in the Diagnostic and Statistical Manual of Mental Disorders (DSM-V) in 2013 by the American Psychiatric Association. Withdrawal symptoms  typically occur 12-24 hours after quitting and usually peak between 20-48 hours before dissipating.


Caffeine and its impact on sports performance

There is much debate on whether or not this drug can be considered as an ergogenic aid due to its possible risk factors however, an article published in 2010 by “The Journal of the International Society of Sports Nutrition” has shed some light on the matter.

The study shows that caffeine can be considered an ergogenic aid in trained athletes when consumed in low-moderate dosages (3-6 mg/kg), however an increase in overall performance is not correlated with an increase consumption. The study also discusses that in an anhydrous state (without water e.g. powder) proves a greater ergogenic aid when compared to coffee.

The study further elaborates on how during long bouts of exercise or during sleep deprivation phases, caffeine can improve vigilance.

Along with improving vigilance it has been shown to be exceptionally effective in time trial performances as well as sustained maximal endurance exercise, caffeine has also proven to be effective in intermittent high intensity sports such as soccer and rugby with equal fruition when tested in a strength/power training setting. When considering diuresis, the study showed no harmful effects on fluid balance that would prove detrimental to performance.

If you would like to know more about caffeine supplementation in regards to sport supplementation, consider reading the blog recently published on Fitbook which covers pre-workout supplementation.


Potential risk factors and vulnerable demographics

Although caffeine has been deemed a non-addictive substance it does come with its fair share of risk factors, some of which are applicable to specific demographics, the upper limit for caffeine intake has been set at approximately 10g for the average adult, considering that an average cup of coffee is approximately 100-200mg, to consume so much is exceptionally rare, but not impossible. If you rarely consume caffeine, you may experience some worrying side effects depending on sensitivity even when consuming less than the average upper limit of 400mg/day. If you experience any of the following symptoms you may be showing signs of a caffeine overdose:

  • Dizziness
  • Heart palpitations
  • Dehydration
  • Chest pain
  • Convulsions
  • Diarrhea
  • Vomiting
  • Fever
  • Headache

Caffeine can impact varying demographics in varying ways, such demographics include:

  • Those with mental health disorders- A high intake may worsen symptoms of anxiety and depression.
  • Pregnant women– Studies suggest that an intake of more than 300mg/day can increase the risks of loss of pregnancy, delayed fetal growth, abnormal fetal heart rhythm. Pregnant women should reduce their total daily intake to less than 200mg/day.
  • Sufferers of heart conditions- An increase in heart rate and blood pressure as a result of caffeine intake can put excess strain on the heart and exacerbate any underlying/or current heart conditions.



By Tireoghain O’Neill


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Nehlig A, Daval JL, Debry G. Caffeine and the central nervous system: mechanisms of action, biochemical, metabolic and psychostimulant effects. Brain Res Brain Res Rev. 1992 May-Aug;17(2):139-70. doi: 10.1016/0165-0173(92)90012-b. PMID: 1356551.


Goldstein, E. R., Ziegenfuss, T., Kalman, D., Kreider, R., Campbell, B., Wilborn, C., … Antonio, J. (2010). International society of sports nutrition position stand: caffeine and performance. Journal of the International Society of Sports Nutrition, 7(1), 5.