Caffeine: Why do Athlete and Public Health Recommendations Differ?
Coffee and caffeine use are prevalent throughout sport, as caffeine is known to improve alertness and is often part of a preparatory or competition-day ritual. Aguilar-Navarro et al. (2019) reported that 75% of athletes consume caffeine around competition. (1)
When I transitioned from working in the public health/clinical nutrition space and into sport, what surprised me was how different the dosing recommendations seemed to be. Why is the average person limited to 400 milligrams caffeine daily when athletes are recommended caffeine doses based off their body weights that may allow for single doses beyond 400 mg?
In this article, I’m going to review:
How caffeine works.
Dosing: Health versus performance.
How caffeine is metabolized.
Caffeine stacking.
Fun fact: The morning poop.
This is part one of a two-part series. Part two will review the benefits, side effects, habitual intake, and caffeine’s role in sleep deprivation.
How Does Caffeine Work?
The blood-brain barrier (BBB) is a “specialized system of brain microvascular endothelial cells that shields the brain from toxic substances in the blood, supplies brain tissues with nutrients, and filters harmful compounds from the brain back to the bloodstream.” (2) Caffeine, however, can pass through the BBB, making the brain one of several tissues that caffeine affects.
Caffeine stimulates the central nervous system and antagonizes adenosine. (3, 4) Adenosine has multiple functions throughout the body, including signaling to other cells, widening blood vessels, and is part of the adenosine triphosphate (ATP) molecule. (4) Within the brain, the natural presence of adenosine “reduces motor activity, decreases wakefulness and vigilance, and decreases the concentrations of stimulatory neurotransmitters.” (4) So, if caffeine can compete with receptors that typically interact with adenosine, blocking it would allow for increased wakefulness, vigilance, and stimulation, plus other outcomes.
Caffeine Dosing: Health versus Performance
From a public health perspective, the maximum recommended daily intake of caffeine is 400 mg, with the European Food Safety Authority recommending no more than 200 mg per dose. (5-8)
To put that into perspective, here’s the caffeine content per common beverage and supplement:
Nespresso coffee pod: 55-85 mg
Starbucks espresso shot: 75 mg
Red Bull: 111 mg per can
C4 Original Pre-workout powder: 200 mg per scoop
Starbucks grande coffee: 330 mg
As standardized as the coffee caffeine values seem, research has shown that brewed coffee contains wildly different caffeine contents—even when brewed by the same source. (9, 10) Given that variance, research designed to evaluate caffeine’s effect on exercise performance often use anhydrous caffeine, or the powdered form of caffeine packaged into a capsule to help standardize and confirm the dose. (11)
Although public health authorities recommend no more than 400 mg per day, athletes receive reputable, science-based recommendations of 3-6 mg per kilogram body weight to be consumed 60 minutes before exercise, with some data showing 1.5-2 mg/kg likely being adequate. (11, 12) Based on weight, that one-time caffeine dose would be the following for the range of 1.5-6 mg/kg:
150-lb. athlete (68 kg): ~100-410 mg.
175-lb. athlete (80 kg): ~120-480 mg.
200-lb. athlete (91 kg): ~135-545 mg.
But athletes are humans, too, falling under public health guidance. For instance, consider the athlete consuming a 200-mg caffeine-containing pre-workout powder before a morning lift, a post-lift Starbucks grande coffee with their breakfast (330 mg), and possibly another hit before an afternoon conditioning or training session (let’s say 111 mg from a Red Bull). All three caffeine doses throughout the day add up to a daily dose of 641 mg—despite consuming single pre-workout caffeine doses under 400 mg.
For dietitians working and student-athletes competing in the NCAA, caffeine is a banned substance at a urine level greater than 15 micrograms/mL (3-5% of the caffeine consumed will leave the body as urine). (4, 12) However, the International Olympic Committee and World Anti-Doping Agency removed caffeine as a controlled substance back in 2004, but continue to monitor it at a urine level of under 12 micrograms/mL, or the equivalent to a caffeine dose of 10 mg/kg. (12)
Caffeine Metabolism, Stacking, and Timing
Metabolism
Although caffeine consumption can appear in the bloodstream within minutes, it peaks within ~30-120 minutes. (5) Nearly 100% of the caffeine consumed will be absorbed, and enters the bloodstream through the stomach and small intestine. (12) The main site of caffeine metabolism is the liver, with liver phase 1 enzyme Cytochrome P450 1A2 (CYP1A2) playing a major role in 95% of caffeine’s clearance. (5, 13) Yet the CYP1A2 gene, and possibly the ADORA2A gene, will influence how quickly or slowly the caffeine is cleared. (12, 14)
For instance, fast metabolizers, or those who seem to drink coffee any time of day with zero-to-minimal effects on sleep, naturally have the AA gene version of the CYP1A2 enzyme, whereas those who are slow metabolizers contain either the CC or AC gene. (5, 12)
For women taking a hormonal oral contraceptive and those who are pregnant, their caffeine clearance appears to become blunted. (5, 12) For instance, oral contraceptives have been shown to increase the rate of clearance upwards of 15.5±0.3 hours. (5) Whereas smokers and those who consume caffeine on a daily basis appear to clear caffeine at a faster rate. (5)
Given the gene matters, as it relates to how quickly caffeine is cleared from the body, the gene directly affects the half-life of caffeine, or the time it takes to metabolize 50% of the caffeine consumed. On average, the half-life is 4-6 hours, but can vary across individuals to be 1.5-10 hours. (4, 12)
Stacking and Timing
Consider the following scenario for a Major League Baseball player with a 7:05pm game start and an individualized half-life of 5 hours.
8am – Triple-shot Americano at breakfast while eating with their kids.
1:45pm – Arrive at the field and eat.
2:45pm – A scoop of pre-workout powder before lifting.
6:15pm – Post-batting practice, pre-game ritual of a doppio espresso, as it’s getting late and they want to improve their focus at the plate.
Midnight – Head to bed.
Seems reasonable, but let's see how caffeine stacking plays out throughout the day:
Tie this together with the adrenaline, crowd excitement, bright lights, fireworks, and loud music at a baseball stadium during a game and you can easily see why sleep for this athlete may be affected.
Fun Fact: Coffee and Poop
The morning bowel movement is a real thing. The coffee bean contains chlorogenic acid that simulates the colon to move, plus the natural morning rise in the hormone cortisol that also stimulates the colon. Coffee plus cortisol equals a reliable morning poop. (15)
Regarding decaffeinated coffee, the colonic stimulus still exists, but is weaker. (16)
Key Takeaways: Advising the Athlete
For those beginning supplementation, start with a low dose: Given everyone tolerates caffeine differently, simply because the athlete dose is 3-6 mg/kg does not mean you need to start at 3 or 6 mg. And just because a scoop of pre-workout contains 300 mg caffeine and that’s what the brand and product’s container recommends, doesn’t mean you have to have the full scoop. Spriet et al. (2020) recommend beginning with ~1.5-3 mg/kg or a standard dose of ~100-200 mg caffeine. (14) Start low, evaluate tolerance, and increase as needed.
Time your dose based on the length of the activity: Given caffeine peaks in the blood ~30-120 minutes after consumption, for a 45-minute lift, you may want to time caffeine 30 minutes prior to. For a 2-hour training session, the traditional dosing 60 minutes before the exercise may be better. For longer events, like a marathon or triathlon, consuming smaller doses of caffeine during the later stages has also been shown productive. (4)
For athletes competing at both the NCAA collegiate and national levels, be mindful of the different blood cut-off values for caffeine for each organization and ensure you have clarity in your caffeine dosing plans from each.
If using liquid caffeinated options to hit the performance dose, consider the athlete’s training or competition type. For instance, if you recommended 300 mg caffeine in the form of Red Bull, that would be roughly three cans and ~25 ounces of fluid. For runners, that much fluid may cause discomfort (some research has noted that higher fluid volumes don’t affect cycling performance). (17, 18)
References
(1) Aguilar-Navarro, M., Muñoz, G., Salinero, J.J., Muñoz-Guerra, J., Fernández-Álvarez, M., … & Del Coso, J. (2019). Urine caffeine concentration in doping control samples from 2004 to 2015. Nutrients,11(2):286. https://pubmed.ncbi.nlm.nih.gov/30699902/
(2) Persidsky, Y., Ramirez, S.H., Haorah, J., & Kanmogne, G.D. (2006). Blood-brain barrier: structural components and function under physiologic and pathologic conditions. J Neuroimmune Pharmacol,1(3):223-36. https://pubmed.ncbi.nlm.nih.gov/18040800/
(3) CPSDA. (2014). Caffeine and athletic performance [Handout]. SportsRD.org. https://www.sportsrd.org/wp-content/uploads/2018/11/Caffeine_and_Athletic_Performance_WEB.pdf
(4) Burke, L., Desbrow, B., & Spriet, L. (2013). Caffeine for Sports Performance. Human Kinetics.
(5) Agostini, C., Canani, R.B., Fairweather-Tait, S., Heinonen, M., Korhonen, H., … & Vergagen, H. (2015). Scientific opinion on the safety of caffeine. EFSA Journal,13(5):4102. https://efsa.onlinelibrary.wiley.com/doi/10.2903/j.efsa.2015.4102
(6) European Food Safety Authority. (2015). Caffeine [Handout]. EFSA.Europa.eu/en https://www.efsa.europa.eu/sites/default/files/corporate_publications/files/efsaexplainscaffeine150527.pdf
(7) Government of Canada. (2022, July 20). Caffeine in foods. https://www.canada.ca/en/health-canada/services/food-nutrition/food-safety/food-additives/caffeine-foods.html
(8) U.S. Food & Drug Administration. (2023, September 7). Spilling the beans: how much caffeine is too much? https://www.fda.gov/consumers/consumer-updates/spilling-beans-how-much-caffeine-too-much
(9) Desbrow, B., Hughes, R., Leveritt, M., & Scheelings, P. (2007). An examination of consumer exposure to caffeine from retail coffee outlets. Food Chem Toxicol,45(9):1588-92. https://pubmed.ncbi.nlm.nih.gov/17412475/
(10) McCusker, R.R., Goldberger, B.A., & Cone, E.J. (2003). Caffeine content of specialty coffees. J Anal Toxicol,27(7):520-2. https://pubmed.ncbi.nlm.nih.gov/14607010/
(11) Pickering, C., & Grgic, J. (2019). Caffeine and exercise: what’s next? Sports Med,49(7):1007-30. https://pubmed.ncbi.nlm.nih.gov/30977054/
(12) Guest, N.S., VanDusseldorp, T.A., Nelson, M.T., Grgic, J., Schoenfeld, B.J., … & Campbell, B.I. (2021). International society of sports nutrition position stand: caffeine and exercise performance. J Int Soc Sports Nutr,18(1):1. https://pubmed.ncbi.nlm.nih.gov/33388079/
(13) dePaula, J., & Farah, A. (2019). Caffeine consumption through coffee: content in the beverage, metabolism, health benefits and risks. Beverages,5(2):37. https://www.mdpi.com/2306-5710/5/2/37
(14) Spriet, L.L. (2020). Caffeine and exercise performance: an update. SSE,29(203):1-5. https://www.gssiweb.org/docs/default-source/sse-docs/spriet_sse_203_a03_final.pdf?sfvrsn=2
(15) Duker Freuman, T. (2020). The Bloated Belly Whisperer. St. Martin’s Griffin.
(16) Boekema, P.J., Samsom, M., van Berge Henegouwen, G.P., & Smout, A.J. (1999). Coffee and gastrointestinal function: facts and fiction. A review. Scand J Gastroenterol,34(230):35-9. https://pubmed.ncbi.nlm.nih.gov/10499460/
(17) Backes, T.P., & Fitzgerald, K. (2016). Fluid consumption, exercise, and cognitive performance. Biol Sport,33(3):291-6. https://pubmed.ncbi.nlm.nih.gov/27601785/
(18) Backx, K., van Someren, K.A., & Palmer G.S. (2003). One hour cycling performance is not affected by ingested fluid volume. Int J Sport Nutr Exerc Metab,13(3):333-42. https://pubmed.ncbi.nlm.nih.gov/14669933/
