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Caffeine: The pros and cons for endurance athletes

The list of possible ergogenic aids for athletic performance is endless (as always, the critical word being “possible”.) One commonly used by both recreational and elite athletes alike is caffeine. In fact, caffeine is a common stimulant used amongst the entire population, typically as a morning or mid-afternoon pick-me-up. A report by the FDA in 2012 showed the average American adult consumes 300mg of caffeine per day – that’s roughly equivalent to the amount of caffeine in a Starbucks’ grande (16oz) dark roast. So should caffeine become a part of your athletic fueling repertoire? Let’s take a look at the pros and cons:


1)      It may improve endurance performance. There are many, many studies showing caffeine can improve endurance performance – but there are also studies showing no effect. This is likely because of the wide variability in factors affecting performance and inability to control for all of them. For example, studies have looked at caffeine’s performance impact for sleep-deprived athletes; athletes in a carbohydrate depleted state; athletes in a carbohydrate repleted state; caffeine pills vs coffee or soda; athletes participating in multi-day events or hot environments. There are also wide study variations in the timing and dosage of caffeine.

The reason for improved performance is still not entirely understood either. One theory is the increase in free fatty acid or muscle triacylglycerol utilization, thereby sparing glycogen use; however, a more promising theory focuses on the brain. Caffeine competes with adenosine for the same receptors in the central nervous system (CNS). Adenosine is responsible for enhancing our perception of pain and inducing sleepiness – so reduce adenosine uptake and you have a possible explanation for the often reported reduction in perceived exertion and increased alertness.

2)      It’s unlikely to affect hydration. Caffeine has been recognized as a diuretic and there was a time caution was used when recommending its intake in order to prevent dehydration. However, further research has identified this diuretic property is really only a concern at certain intake levels. For most individuals, it would take consuming over 400mg in a 24 hour period before the caffeine starts contributing to fluid loss. So the fluid you consume as coffee actually counts towards your total daily intake.

3)      Withdrawal isn’t required. Another common assumption was that an individual who routinely consumed caffeine would need to “abstain” for several days prior to an event in order to get the benefits. Not entirely so, per this 2011 study on cyclists in which no change in performance was observed with identical mg/kg pre-race caffeine dosages between caffeine-consumers abstaining from intake 4 days prior to a race and those maintaining regular intake.


1)      Possible sleep disturbances and irritability. Consuming a grande dark roast right before bed probably strikes most folks as an unfavorable idea, but the reality is caffeine can keep on ticking in your system for far longer than just an hour or two. For some, caffeine may still be circulating 10 hours after consumption. As a result, even an afternoon caffeine jolt can impact your sleep routine.

2)      Gastrointestinal upset. This may not be entirely caffeine per say but rather the form in which you consume it. Some coffee drinkers report it is the key to a pre-race bowel movement, but studies indicate caffeine shows no effect on intestinal motility or increase in gastric emptying. So it’s likely the coffee, not the caffeine. Also, if you plan to reach for a Coke during the last few miles of your marathon or Ironman, keep in mind the carbohydrate content of soda is much more concentrated than a sports drink, which is specifically designed for improved absorption. This could lead to cramping and diarrhea, so be certain to test it before the race.

3)      Very individual. Responses to caffeine can vary. Some can drink 24oz of coffee and not notice a thing, while others consume 6oz and experience irritability and increased heart rate. You have to test it to find out what works or doesn’t work for you.

4)      Withdrawal symptoms. If you DO decide you want to reduce your caffeine intake, you may experience withdrawal symptoms. The most common complaints – headache and “moodiness”.


1)      If you choose to consume caffeine as part of your fueling plan, most evidence indicates roughly 3gm/kg in a dose is appropriate. This equates to about 200mg caffeine for a 150lb individual. Dosages above 6mg/kg are correlated with more of the side effects discussed above and don’t appear to have any greater benefit. Caffeine can be consumed in the 30-60 minutes leading up to an event and periodically throughout for those races in excess of 2 hours.

2)      Identify your individual tolerance. Everyone responds a little bit different to caffeine. Practice consuming it surrounding workouts that mimic your race intensity, and be aware of how your gut will respond pre-race, especially for coffee drinkers (porta potty access?). Also, pay attention to any changes in sleep cycle or mood if you are increasing or decreasing your intake.

3)      Take note of your daily caffeine intake. Caffeine isn’t “bad”, but consuming it in amounts greater than 400mg/day may be a sign you are masking other issues – in particular, a lack of sleep or fatigue from overtraining. Enjoy your daily cup(s) o’ joe, but get to the root of the problem if caffeine intake is the only way you can make it through the day.

4)      Finally, be certain to first assess your other basic-but-highly-linked-to-performance factors before relying on caffeine for a boost: adequate calorie and carbohydrate intake, appropriate sleep quality and quantity, adequate hydration, etc. are all far more important for an athlete than relying on caffeine.

Keep in mind caffeine is being added to more and more things these days. Be certain to look at labels, and recognize another common ingredient which also provides caffeine: guarana.


ITEM                                  SERVING                           CAFFEINE (MG)

Coffee (brewed)             8oz                                     95-200*

Espresso                           1oz                                     47-75*

Tea (black)                       8oz                                     14-70*

Tea (green)                      8oz                                     24-45*

Soda, Coke                       12oz                                   23-35

Soda, root beer               12oz                                   0

Red Bull                            8oz                                     75-80

Perky Jerky                       1oz                                     35

Chocolate                         ½ cup                                 52

Gu (Espresso)                   1 packet                            40

Data provided by the USDA Nutrient Database and brand-specific nutrition information

*Values vary by roast, brand

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