What is Caffeine?
Caffeine is a natural stimulant most commonly found in coffee, tea, cacao, chocolate and various energy drinks. It has been consumed for centuries, with its use dating back to ancient civilizations that brewed tea and coffee to provide instantaneous energy. There is some suggestion that caffeine or coffee specifically has shaped the world we live in. Today, it is widely known and understood for its benefits in improving mental and physical performance, potentially improving cognitive functions such as memory, focus, and reaction time, as well as boosting physical endurance by increasing adrenaline, making it a popular supplement among athletes and professionals alike.
Recent research has investigated the mechanisms of action by which caffeine might benefit both mental and physical performance. This research confirms that caffeine acts primarily as an adenosine receptor antagonist, which prevents drowsiness and increases alertness. It is also known to influence noradrenaline and dopamine release, which are the mechanisms by which it improves cognitive functions like learning and memory. Caffeine can also impact energy metabolism throughout the brain but may reduce cerebral blood flow, causing relative brain hypoperfusion.
Physically, it may improve motor activity and coordination within the muscle with its psychostimulant effects, also increasing arousal and vigilance (Nehlig et al., 1992). Caffeine may also promote through its actions on adenosine receptors and epinephrine, leading to increased fat oxidation (the breakdown of fat) and energy availability during physical activity, especially submaximal aerobic exercise (Acheson et al., 2004; Fernandez-Sanchez et al., 2024). Research suggests that the magnitude of the effect of caffeine on fat oxidation during fed-state exercise may be affected by the dose of caffeine administered (higher with <6mg/kg of bodyweight than >6mg/kg of bodyweight. It is also suggested that it affects untrained individuals more than aerobically trained individuals.
There is some further suggestion that this might benefit aerobic performance through sparing glycogen (Fernandez-Sanchez et al., 2024) and body composition when combined with an energy restricted, high protein diet (Tabrizi et al., 2019), although that has been debated (Antonio et al., 2024). With regards to strength, Duncan et al.’s (2019) research found improvements in upper and lower peak power following caffeine ingestion.
Following this brief summary, this article will now break down the research on caffeine with respect to health, hydration, cognitive performance, physical performance, and sleep. It will also present some natural caffeine sources, as well as discussing some of the research regarding caffeine dosage for performance benefits. It will also present positions on some of the myths and misconceptions regarding caffeine.
Health Research on Caffeine
There is a key factor that must always be considered when taking caffeine, especially in high doses; the issue of anxiety risk. A recent meta-analysis found that caffeine does increase the risk of anxiety. The meta-analysis confirms that low doses of caffeine moderately increases anxiety risk, while high doses (>400mg) have a more substantial impact (Liu et al., 2024). Whilst moderate caffeine intake may offer temporary relief from certain depressive symptoms and even potentially improve mood for some individuals via the mechanism of neurotransmitter release, including serotonin and dopamine, consumers should be aware that excessive consumption of caffeine can worsen anxiety, disturb sleep, and result in adverse mental health consequences (Antonio et al., 2024).
L-theanine is an amino acid found in tea, which has been shown to potentially alleviate anxiety and stress associated with caffeine intake. It works by increasing the production of alpha waves in the brain, which promote a state of relaxation without drowsiness. L-theanine also modulates neurotransmitter levels, such as dopamine and serotonin, contributing to its calming effects (Wang et al., 2022).
The discussion around the synergistic effects of L-theanine and caffeine on cognitive function are particularly noteworthy. Studies indicate that while caffeine alone benefits mental and physical performance, it might come at a physiological and psychological cost that could ultimately be of detriment to performance. When caffeine is combined with L-theanine, these negative side effects can be mitigated, leading to better cognitive performance without the associated anxiety. A study by Sohail et al (2021) found that the combination improved cognitive performance and reduced mental fatigue more effectively than either substance alone. The researchers confirmed that L-theanine is both a safe and effective cognitive enhancer.
Caffeine’s Effects on Hydration
There is some suggestion that caffeine consumption (from coffee) might result in dehydration. Research has shown that moderate coffee consumption does not lead to dehydration and can contribute to daily fluid intake similarly to water. Studies often find that drinking coffee in normal amounts (e.g., 3-4 cups per day) does not negatively impact hydration status. This was confirmed by Armstrong et al., (2005) who found no significant difference in hydration markers between caffeine supplementation and no caffeine supplementation over a 24-hour period.
In the book Caffeine for Sports Performance, Burke et al. conclude that moderate caffeine consumption does not pose a significant risk to hydration status, with tolerance to caffeine's diuretic effects developing within 4-5 days of regular intake.
Further studies (Killer et al., 2014) show that caffeine intake, even at moderate levels (up to 6 mg/kg), does not significantly affect total body water balance or fluid retention, and its effects on urine output are minimal and transient. Although higher doses (6 mg/kg or more than 500 mg) may induce acute elevation of urine output (Antonio et al., 2024).
Caffeine’s Effects on Cognitive Function
Unsurprisingly, caffeine intake can have a significant impact on cognitive function, with statistically significant improvements noted in research depending on the specific task and the dosage consumed. A meta-analysis of 13 studies revealed that low to moderate doses of caffeine before and during exercise significantly improves self-reported energy, mood and cognitive functions such as attention, accuracy, and processing speed in cognitive tasks within a sporting context (Calvo et al., 2021). Another study in occupational performance reported similar improvements across alertness, vigilance, reaction time and attention, with less consistent effects being observed on memory and higher order executive function (McLellan et al., 2016). The authors conclude that caffeine intake is an effective strategy to improve occupational performance, especially those who require optimal physical and cognitive function.
Caffeine’s Effects on Performance
Caffeine is perhaps the most commonly consumed ergogenic aid in the sporting context, with even the placebo effect of caffeine being known to improve performance (Antonio et al., 2024). Research has consistently demonstrated that its consumption prior to and during exercise can benefit performance in a variety of events. An umbrella review of 21 meta-analyses published in 2020 confirmed this. The research indicates that caffeine significantly improves aerobic endurance, muscle strength, muscle endurance, power, jumping performance, and speed (Grgic et al., 2020).
A more recent meta-analysis of 21 studies reported that caffeine ingestion can increase time to exhaustion by 39.2% and reduce time to complete time trial events in both recreational and well-trained individuals compared to placebo (Wang et al., 2022). An earlier meta-analysis found that caffeine can significantly improve speed during intense endurance events, such as time trials, CrossFit or Hyrox events (Christensen et al., 2017).
Strength has been shown to be significantly improved with caffeine intake too. A meta-analysis of 10 studies indicated that caffeine ingestion significantly improves both muscle strength and muscle power. The improvement was shown to be more pronounced in upper body strength compared to lower body strength (Grgic et al., 2018).
There is also evidence that caffeine can benefit skill performance in various sports such as football, basketball, tennis, rugby and more (Foskett et al., 2009; Portillo et al., 2017; Calvo et al., 2021). Sports which involve a predominance of non-oxidative metabolism, requiring high movement velocity and power such as combat sports have also been shown to be benefitted from caffeine ingestion. A meta-analysis of 26 studies reported that caffeine may be ergogenic for a range of combat sports aspects involving isometric strength, anaerobic power, reaction time and anaerobic metabolism, with a particular note on caffeine showing an improvement in Judo athletes’ grip strength (Delleli et al., 2022).
The Performance Mechanisms of Caffeine
These improvements could, in part, be related to a possible increase in carbohydrate oxidation seen with caffeine ingestion. Higher rates of carbohydrate oxidation are generally associated with higher exercise intensities. A recent study reported that caffeine significantly increases carbohydrate metabolism during physical activity. More specifically, they reported that caffeine increased exogenous carbohydrate oxidation by 26%. The authors of the paper suggest that total carbohydrate oxidation rates were highest when caffeine was ingested with glucose, compared to glucose alone and water (Yeo et al., 1985).
Interestingly it has also been reported that caffeine may also help accelerate rates of refueling after intense exercise too. Research has demonstrated that the co-ingestion of caffeine (8 mg/kg) with carbohydrates resulted in a 66% higher rate of muscle glycogen resynthesis over a 4 hour recovery period compared to carbohydrates alone. After 4 hours, glycogen accumulation was significantly higher with caffeine (313 ± 69 mmol/kg) compared to carbohydrates alone (234 ± 50 mmol/kg) (Pedersen et al., 1985). This is of particular relevance to those who compete in high intensity events with very short recovery periods between events or heats, such as swimming, track events or combat tournaments.
Caffeine’s Effects on Sleep
All good things come at a cost however, and caffeine is no different. Its ability to stimulate the central nervous system is generally known to impair sleep, if consumed in excessive quantities in close proximity to bed time.
A meta-analysis of 24 studies confirmed that caffeine intake can reduce total sleep time by 45 minutes, reduce sleep efficiency by 7%, increase the time taken to fall asleep by 9 minutes, but perhaps most significantly reduce deep sleep and increase light sleep duration. They also found that there was an increase of wake after sleep onset of 12 minutes. The authors of the meta-analysis suggest that coffee, with around 107 mg of caffeine per 250 ml, should be consumed at least 8.8 hours before bedtime, while pre-workout supplements containing around 220 mg of caffeine should be consumed at least 13 hours before bedtime to avoid any interference (Gardiner et al., 2023). An additional study demonstrated that even when consumed 6 hours before bed, caffeine can significantly disrupt sleep (Drake et al., 2013).
These sleep disruptions can, in turn, lead to impaired daytime functioning, creating a cycle where individuals use more caffeine to counteract sleep deficits (O'Callaghan et al., 2018). However, it should be noted that when sleep deprived, caffeine can certainly help overcome fatigue. A meta-analysis which specifically looked at the impact of acute caffeine consumption in sleep deprived individuals showed that caffeine significantly improved response time, accuracy on attention tests, executive function, reaction time, and vehicular control measures. The meta-analysis highlights that caffeine can effectively counteract the cognitive and physical impairments due to sleep loss, improving overall performance (Irwin et al., 2020).
Myths and Misconceptions of Caffeine
In recent years there has been a growing narrative around the benefits of delaying caffeine intake upon waking, by 90 to 120-minutes. This recommendation was purported on a popular health and wellness podcast and gained significant traction, despite the body of scientific evidence showing this to be factually incorrect.
Antonio et al., (2024) examined this theory in detail and the following is a direct quote from the conclusions, “In summary, though there may be an upside to delaying morning caffeine intake under conditions of sufficient sleep, this has to do with the magnitude of effect rather than proposed mechanisms related to prolonging the cortisol peak, continued declines in adenosine, or avoiding an afternoon “crash. A significant drawback in the argument related to cortisol is that a similar effect occurs with intense resistance exercise performed soon after waking. Following this line of reasoning would imply that this type of early morning exercise should be avoided; however, this notion makes no scientific or pragmatic sense. The suggestion that adenosine continues to decline upon waking is also scientifically inaccurate and not supported by research. There is also no evidence that caffeine ingestion upon waking is somehow responsible for an afternoon “crash” or that delaying consumption would somehow prevent this if it did occur.”
That being said, the current evidence does not support the notion that you need to delay the intake of caffeine or any caffeine containing product upon waking.
Some other common misconceptions discussed within this paper include caffeine and heart health, with the authors reporting that low to moderate intakes of caffeine do not have any adverse effects on cardiac muscle. The paper also covered the link between caffeine and bone health, suggest that ≤ 4 cups of coffee (≤400 mg of caffeine) is the threshold for concern regarding BMD and/or fracture risk, primarily in females. The authors also suggest the current mechanistic evidence and SUD criteria do not fully support the classification of caffeine as addictive (Antonio et al., 2024).
Sources of Caffeine
As previously mentioned, caffeine is found naturally in various foods, although most commonly consumed in the form of tea, coffee, chocolate and energy drinks.
A standard 8-ounce cup of coffee contains about 95mg of caffeine and a single shot espresso around 65mg. Black tea has roughly 47mg per 8-ounce serving, while green tea contains about 28mg. A 12-ounce can of cola typically has 22-46 mg.
Energy drinks can vary widely, with some containing up to 160mg per 16-ounce serving. Dark chocolate has around 12mg per ounce, and milk chocolate contains about 9mg per ounce. Additionally, some over-the-counter supplements, pre-workout products, energy drinks and medications can contain 30 - 400 mg of caffeine per serving.
Interestingly, it is worth noting that the caffeine content of coffee can vary significantly. A study in 2007 analysed 97 espresso samples and found a wide range in caffeine content, from 25mg to 214mg per serving. On average, the caffeine content was 106mg per serving, with a standard deviation of 38mg. This significant variance indicates that consumers may be exposed to highly differing caffeine doses at regular coffee outlets (Desbrow et al., 2007). The same researchers also found a wide range of caffeine, from 91 to 387mg per serving in 15 popular pre-workout supplements. The caffeine content varied significantly within and between product batches, with discrepancies ranging from 59% to 176% of the amounts claimed on product labels. This indicates that consumers could be exposed to inconsistent caffeine doses, even if they are consistently using the same product, potentially affecting their performance and health (Desbrow et al., 2019).
What Dosage of Caffeine is Effective?
A paper from the Journal of the International Society of Sports Nutrition provides detailed guidelines on caffeine dosage for improving cognitive function and physical performance. They note that doses of 200mg significantly improved vigilance, reaction time, and alertness in sleep-deprived conditions, with no added benefit at 300 mg compared to 200 mg. This research also found that higher doses of 3-6 mg/kg of body weight improved endurance performance (Guest et al., 2021). This appears to suggest that lower dose caffeine might be more beneficial in sports that require focus and attention, such as team and combat sports, whereas endurance events that rely primarily on physical attributes can benefit from the higher dosages. Furthermore, they discuss how very high doses of caffeine (such as 9mg per kg of bodyweight) are associated with high incidences of side-effects whilst also not being required for a positive performance effect.
Various studies have investigated the effects of lower doses of caffeine, around 1-2 mg/kg body weight on performance. A meta-analysis found that these low doses of caffeine had significant ergogenic effects on resistance exercise performance, with improvements in muscular strength, muscular endurance, and mean velocity, with the magnitude of effects being similar to those earlier reported with higher caffeine doses (Grgic, 2022). Another review paper explored the impact of doses ≤3 mg/kg. It finds that low doses can improve cognitive function and physical performance, with benefits such as increased alertness and reaction time (Pickering & Kiely, 2019). These results suggest that even low doses of caffeine around 100mg can be beneficial for improving both cognitive and physical performance. Our Energy Hydration Sachets contain 100mg of caffeine per serving. If you would like to sample our full range of electrolyte sachets, be sure to explore our variety pack of hydration sticks.
Caffeine Habituation
Caffeine habituation (otherwise known as caffeine tolerance) refers to the idea of reduced responsiveness to caffeine's stimulatory effects after regular consumption. Studies have shown conflicting results, with some suggesting that habitual caffeine consumers may develop a tolerance, resulting in diminished effects on alertness and performance over time and others showing no evidence of habituation. A study by Lara et al., 2019 showed that caffeine increased peak cycling power by approximately 4% for the first 15 days, but this effect diminished with continued use, indicating tolerance development. Additionally, caffeine improved peak power during the Wingate test by around 4.9% on specific days, with the highest magnitude of effect being on the first day, following which it gradually declined, suggesting progressive tolerance over time.
Another systematic review and meta-analysis of 60 studies on this topic made conclusions that habitual caffeine consumption does not influence the acute performance-enhancing effects of caffeine. The analysis showed a significant ergogenic effect for low doses of caffeine below 3 mg/kg and between 3-6 mg/kg. Overall, the benefits were consistent across different exercise types and regardless of the duration of caffeine withdrawal before exercise (Carvalho et al., 2022).
Conclusion
To conclude, caffeine is a powerful natural stimulant which offers numerous benefits for mental and physical performance. Its ability to improve alertness, focus and physical endurance can make it an excellent supplement choice amongst both athletes and professionals. The research presented in this article discusses how caffeine primarily acts as an adenosine receptor antagonist, increasing alertness by influencing neurotransmitter release, which may improve cognitive functions. In terms of physically, it has effects on energy metabolism and fat oxidation which can improve performance.
The discussion of caffeine would be incomplete without some further considerations. High doses can increase anxiety risk and disrupt sleep, and habitual use may lead to tolerance over time. Research has shown that combining caffeine with L-theanine may mitigate some of the negative effects of caffeine, providing the cognitive benefits whilst potentially reducing the likelihood of anxiety-events.
In terms of hydration, the research shows that when consumed in moderate amounts, caffeine may not significantly impact our hydration. Furthermore, its ability to accelerate glycogen resynthesis after exercise may offer further benefits for athletes.
Despite its benefits, caffeine consumption should be moderated to avoid problematic effects on sleep and mental health. As with any supplement, individual responses can vary, and so if you have any questions about how much caffeine is safe for you to have, you should consult a medical professional.
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