Can caffeine harm performance?
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Can caffeine harm performance?

Caffeine is a widely used supplement used to enhance performance in endurance, strength and combat sports. Today we’ll discuss the flip side: Can caffeine harm performance?

What is caffeine?

Caffeine is a substance that “occurs naturally in foods, such as coffee, tea and cocoa and has a long history of safe use as a mild stimulant. Products are also available with added caffeine, including cola-type soft drinks, formulated caffeinated beverages (energy drinks) and energy shots.”(1)

How can caffeine harm performance?

Physiological effects of caffeine

Doses within the recommended doses of 3-6mg/kg of body weight can increase heart rate and blood pressure, diminish attention (2) and cause anxiety (3). Some supplements or beverages containing caffeine can also cause stomach distress, such as acid reflux.

Sleep and recovery

Moreover, it is well known that caffeine affects sleep negatively (2, 3). Therefore, caffeine supplementation can be detrimental for recovery and subsequent performance, especially if taken in the afternoon or evening.


Caffeine has been regarded as a diuretic, meaning that it increases the production of urine. This could lead to dehydration (or lack of proper rehydration post-event). However, it seems that the diuretic effects of caffeine have been overstated. In addition, this effect is smaller in habitual consumers of caffeine and the potential greater fluid losses could be offset by a greater fluid intake (4).

Factors affecting caffeine metabolism


Each person’s genetic makeup will determine how caffeine affects them with regard to anxiety, sleep disturbances and performance improvements. Single nucleotide polymorphisms in the genes CYP1A2 and ADORA2A seem to be responsible for caffeine metabolism in regard to performance. Fast metabolisers (AA genotype) will likely experience beneficial effects, while slow metabolisers (CC genotype) will potentially experience decreased performance. Those in the middle (AC genotype) are not likely to experience an effect either way. For slow metabolisers, the negative effect of caffeine in performance could be mitigated by consuming it longer before the event (e.g. 60 minutes off) (3).

Training age

It seems that untrained individuals will experience greater improvements in performance with caffeine supplementation than their trained counterparts. It is not clear if this is due to the physiological action of the caffeine or because there is very little room for improvement in trained athletes (3).


Women seem to metabolise caffeine slower than men. This means that ladies might benefit from taking caffeine longer before training or competition, as discussed in the Genetics section above (3).

Summary and recommendations

Caffeine can be detrimental for performance for some individuals.

Don’t take caffeine supplements if:

  • You know it causes detrimental health or performance effects in you.
  • You are a child or teenager.
  • You are pregnant or breastfeeding.

If you do want to test if caffeine supplements work for you:

  • Try a few different types and see which one works best for you. If you compete, make sure the products you try have been tested for banned substances.
  • Do not take pure caffeine powder, which can be lethal in small quantities (1).
  • While some energy drinks might be used as a performance booster, most of them contain excess sugar and other substances that might be detrimental for health (5).
  • Try a few different doses keeping your diet and training relatively equal to see which one works best for you.
  • If you are a fast metaboliser of caffeine, supplement 15-30 minutes before the event, otherwise do it around 60 minutes prior. If you are female, chances are you metabolise caffeine slower than the gents, so try a longer window as well.
  • If you are a competitive athlete, avoid relying on coffee as a supplement because the actual caffeine content is extremely variable.
  • As always, talk to a sports dietitian to discuss your nutrition and supplement strategy.


  1. Food Standards Australia & New Zealand. Caffeine 2019 [Available from:].
  2. Lopez-Gonzalez LM, Sanchez-Oliver AJ, Mata F, Jodra P, Antonio J, Dominguez R. Acute caffeine supplementation in combat sports: a systematic review. J Int Soc Sports Nutr. 2018;15(1):60.
  3. Pickering C, Grgic J. Caffeine and Exercise: What Next? Sports medicine (Auckland, NZ). 2019;49(7):1007-30.
  4. Clinical Sports Nutrition. Burke L, Deakin V, editors. North Ryde NSW: McGraw-Hill Education (Australia) Pty Ltd; 2015.
  5. Campbell B, Wilborn C, La Bounty P, Taylor L, Nelson MT, Greenwood M, et al. International Society of Sports Nutrition position stand: energy drinks. Journal of the International Society of Sports Nutrition. 2013;10(1):1.

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