Caffeine is the most widely-used performance enhancer in all of sport—with about 90% of the world’s population consuming caffeine on a daily basis, it’s a nearly universal part of the human diet, and its benefits on endurance performance are well-established.
When it comes to a one-off race or workout, there’s no doubt that taking some caffeine about an hour beforehand will lead to a noticeable boost in performance.
However, new research has raised some questions about the specifics of caffeine usage that might make some runners second guess their caffeine habits.
The concerns have to do with the long-term effects of caffeine, as well as what scientists call “indirect effects”—secondary effects of caffeine like sleep disturbance, anxiety, or tolerance.
We’ll take a look at the current state of research to see whether you should alter your caffeine intake as a result of these new findings.
Building up a tolerance to caffeine over time
Most of the “classic” research on caffeine intake and athletic performance goes as follows: a group of athletes is split into two groups, one of which receives a placebo, while the other receives a caffeine pill.
Then, both groups undergo some type of exercise test, whether it’s a treadmill protocol, a cycling time trial, or a shuttle run.
When these studies are conducted, researchers usually ask the participants to abstain from caffeine for at least a week before the study.
There’s a good reason for this decision: given that most of the people in the study are likely to use caffeine on a regular basis, failing to control for caffeine intake in the days leading up to the study would put the placebo group at a big disadvantage, as they’d be suddenly thrown into caffeine withdrawal.
A new paper published in 2019 by researchers in Spain argues that these classic studies might have missed something important [1]—if you’re already accustomed to a high level of caffeine intake, do you still get a benefit from it?
They designed a study to investigate this question.
Their participants took caffeine or a placebo every day for 20 consecutive days, and underwent an aerobic endurance test on an exercise bike three times per week throughout the study. This clever design allowed the researchers to track the time-course of the performance-enhancing effects of caffeine, as they had three exercise sessions every week for three weeks to compare caffeine to placebo.
Two important findings came out of the results:
- First, even late in the study, caffeine still improved performance compared to a placebo.
- Second, there was some evidence that the performance benefits were attenuated later in the study. The differences were not huge, and the statistical evidence was not completely clear, but there was a trend towards a smaller benefit from caffeine by the end of the study. The authors argue that these findings could mean that your body acclimates to the effects of caffeine, and that you may not sustain the same endurance benefits after chronic caffeine use that you would have gotten if you taken it “fresh.”
Other effects of caffeine tolerance
While it might be desirable to squeeze out a bigger performance benefit by tapering off caffeine before a big race, there are a few other components of caffeine tolerance that need to be taken into account.
Most importantly, when you stop taking caffeine, you may experience some symptoms of caffeine withdrawal: fatigue, headaches, anxiety, and irritability, according to a review article by Terry E. Graham at the University of Guelph in Canada [3].
These symptoms are at their worst about two days after you stop taking caffeine, but can last for up to a week.
Moreover, when you take caffeine again, the effects will hit you harder–that means a greater potential for sleep disturbances, nausea, and jitters, particularly with higher doses of caffeine. These all relate to the “indirect effects” mentioned earlier.
Does everyone benefit from caffeine?
Another analysis of the same data by the team in Spain tested the idea of whether some people truly don’t respond to caffeine—something that had been reported in earlier research [2]. This analysis looked at subject-specific responses across the course of the study.
Since they had eight separate exercise sessions for each person, comparing caffeine to placebo, the researchers had a lot of data to assess whether some people really do fail to respond to caffeine.
The analysis showed that all of the study participants experienced a benefit from caffeine, but to vastly different degrees. The range of benefits was from a 1% improvement all the way up to a 9% improvement.
So, while this study lays to rest the idea that some people see no benefit from caffeine, it does highlight the fact that some people will get a much bigger benefit than others.
What else could affect your reaction to caffeine during running?
A recent review article published in the journal Sports Medicine cites some fascinating new research indicating that the relationship between caffeine and performance might be far more complex than originally thought [4].
Preliminary data suggest that certain genes influence your body’s response to caffeine—this might account for why some people seem to gain a greater benefit from caffeine than others.
Other research suggests that caffeine could help enhance the storage of muscle glycogen, which would provide a strong argument not to stop taking caffeine in the week leading up to a big race.
The bottom line: should you change up your caffeine habits to run better?
While it might seem like all this new research raises more questions than it answers, there are a few solid takeaways that can be drawn from these findings.
First, regardless of whether or not you abstain from it before a big race, caffeine is likely to help you perform better.
Second, the safest bet appears to be reducing, but not totally eliminating, your caffeine intake in the week or two leading up to race day.
Total caffeine abstinence might lead to a slightly bigger boost from caffeine on race day, but may also leave you more vulnerable to unwanted side effects, like jitters and anxiety, that can be caused both by withdrawal and by an increased sensitivity to caffeine’s effects when you start taking it again.
If you do decide to cut off caffeine intake completely when you have a big race coming up, make sure you abstain from caffeine for at least 10 days—it can take a full week for the effects of caffeine withdrawal to completely wear off.
Like many things in training, it appears that moderation is the best course of action when it comes to using caffeine to fuel better running performance.
