The Role of the Immune System in Sports Performance
The immune system is our body’s defence system against external elements such as viruses, bacteria, and fungi.
There are several supplements to improve sports performance. However, only a few of them are scientifically proven to be effective. Caffeine is probably one of the most consumed substances by the adult population in general, and interestingly, one of the most contrasted ergogenic aids.
Besides bringing certain benefits to health, caffeine could improve performance through central and peripheral mechanisms. For example, it boosts the nervous system activation increasing the production of catecholamines and endorphins, and activating the muscles.1 Moreover, it has been suggested that caffeine could partly attenuate the feeling of pain, which would increase tolerance of highly intense training. What is more, although there is a little controversy regarding its effects on muscles,2 caffeine could improve the activity of sodium-potassium pump (Na + /K + ATPase), reducing the build-up of potassium at an intracellular level, and therefore, withholding fatigue, as well as contributing to the flow of calcium in muscle cells, improving the processes of muscle contraction. Lastly, largely due to the activation of the sympathetic nervous system, caffeine has shown it increases energy expenditure, the availability of fatty acids in blood and lipolysis.3
Actually, this supplement has shown to be beneficial in very different sports. For example, a recent meta-analysis that included 46 studies, published in the prestigious magazine Sports Medicine, showed that the consumption of caffeine (3-6 mg/kg) improves performance in endurance tests by 3%.4 Similarly, other recent meta-analyses have shown that caffeine supplementation improves muscle strength and power in short-duration exertion, such as a sprint, by approximately 3-4%.5,6
It is worth mentioning that it has traditionally been suggested that caffeine could increase the risk of dehydration due to its potential diuretic effect, especially during training. However, a study led by Dr. Asker Jeukendrup did not find alterations in any markers of dehydration in people who consumed moderately high doses of caffeine (5 mg/kg).7 Furthermore, another study showed that the administration of moderate doses of caffeine (3 mg/kg) did not cause major increases of diuresis, although it did show a slight increase with the intake of high doses (6 mg/kg).8 Therefore, caffeine does not seem to excessively increase the risk of dehydration within usually consumed doses.
Despite its overall effectiveness, it has been suggested that not every person could benefit from this supplement in the same way as a recent systematic review concludes. Some studies have found a high variability (between 0 and 17% depending on the individual) in the benefits obtained after caffeine consumption.9 One of the factors suggested as a possible mediator of caffeine responses is how used someone is to its consumption, given that those who usually consume caffeine could have fewer effects than those who do not. However, a recent study showed that the consumption of 6 mg/kg of caffeine improves performance in time-trailing even in individuals who usually consumed high doses (>300 mg/kg of caffeine per day, equivalent to 3 cups of coffee).10
Also, other studies have shown that caffeine can bring benefits even in people who could be considered non-responders according to their biological responses after intake. For example, a study divided a group of football players into ‘responders’ and ‘non-responders’ based on their blood pressure, glycerol in plasma, free fatty acids, and adrenaline responses (which tend to highly increase after caffeine consumption), after caffeine intake.11 Participants consumed caffeine (6 mg/kg) or placebo, then played two simulated matches on a treadmill, and different markers of performance were assessed, such as the time until exhaustion and the ability to jump. The results showed that caffeine improved markers of performance with regard to the consumption of placebo, in both ‘responders’ and ‘non-responders’, although we have to highlight that ‘responders’ had less perceived exertion.
On the other hand, some studies suggest that genetics (CYP1A and ADORA2A genes in particular) could condition a higher or lower response to caffeine consumption. Thus, focusing on CYP1A gene, rapid and poor metabolisers could be differentiated, being the latter the ones in which caffeine remains in the body for a longer period and the most likely to develop adverse side effects (even greater risk of cardiovascular events) after the intake of high doses of caffeine or energy drinks that combine caffeine with other stimulants, such as taurine.12 In contrast, rapid metabolisers would present a positive response even with relatively high doses of caffeine. A recent study shows that caffeine (3 mg/kg) brought similar benefits in strength training power, the ability to jump, or the power in a Wingate test, in most individuals regardless of whether they are rapid or poor metabolisers (focusing on the CYP1A9 gene).13 In addition, as shown in a recent study published in Nutrients magazine,14 at least 84% of people who have genetics that would condition them as ‘non-responders’ to caffeine focusing on the ADORA2A gene, they performed better with tests such as jump, strength, or the anaerobic capacity after a 3 mg/kg intake.
It has also been suggested that the fact that in some studies a small proportion of participants does not obtain any benefits in their performance could be due to the fact that, even though they did not obtain any benefit at that moment, they may in subsequent occasions. In this sense, a study assessed the effect of having 3 mg/kg of caffeine or placebo during 8 different occasions on the same participants.15 Results showed that caffeine provided benefits between 1% and 9% in performance measured with a Wingate test and an incremental test until exhaustion, and every participant improved their performance in at least 3 out of the 8 visits. Therefore, these results show that even individuals who may be considered non-responders could benefit from the intake of caffeine on subsequent occasions.
Finally, it is important to highlight that in most scientific studies, caffeine is administered in anhydrous form, i.e. pills of about 3 to 6 mg/kg. However, when we talk about caffeine, we usually understand that a cup of coffee could be enough to obtain the benefits described in scientific knowledge. In this sense, a study led by Dr. Asker Jeukendrup compared the effect of having 5 mg/kg of isolated caffeine and the same amount of caffeine from coffee.16 Results showed that both isolated caffeine and coffee improved performance similarly (5% in a bike trial of 45 minutes) compared to the administration of decaffeinated coffee or a placebo substance. Therefore, the administration of the same dose of caffeine, coffee can be considered similarly effective to caffeine pills. Nonetheless, it is important to highlight that getting to the necessary doses (>3 mg/kg) by drinking coffee is much more complicated. For example, considering that a coffee capsule contains approximately 60 mg of caffeine, 3 or 4 capsules (depending on the athlete’s weight) would be necessary to get to the effective amounts of caffeine.
In summary, caffeine can improve performance substantially for the vast majority of the population and in different sports. As long as the right doses are consumed, which tend to be 3 to 6 mg/kg in most studies. Caffeine is an effective aid to improve sports performance.
Pedro L. Valenzuela
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