Caffeine is a naturally occurring chemical found in certain plants including cocoa beans, kola nuts, yerba maté, guarana, and the world’s most beloved tea leaves & coffee beans. Coffee & tea have become the major sources of caffeine intake, and many consider it as an essential dietary component to get them through the day. It is not uncommon for people to drink between 3-6 cups of tea or coffee per day, as they find it helps them to feel better, have more energy and be able to carry out daily tasks more effectively. A cup of strong coffee or a caffeine supplement before training is also common practice for athletes and gym users to improve mental and physical performance.
On the other hand, it is a common belief that drinking caffeinated beverages like tea and coffee can lead to dehydration. Hydration is obviously important for health and exercise performance, but the question is, should caffeine intake be reduced or avoided to maintain fluid balance, and does it actually improve performance?
Caffeine and hydration
Tea and coffee are the most widely consumed drinks in the world, after water. Theoretically, caffeine may have a diuretic effect as it disrupts an important regulator of kidney function, renal water & electrolyte transport, which can stimulate urine output causing water & electrolyte loss (Rieg et al., 2005). This has led to the belief that regular caffeine intake results in dehydration and some studies have supported this theory. However, these studies report a range of caffeine forms and doses in populations who do or do not regularly consume caffeine containing beverages. Together, these data suggests that high doses of caffeine (>500mg) can increase urine volume in caffeine-naïve (non-regular consumers) individuals, but low to moderate doses (<250mg) do not induce a diuretic effect.
Regular caffeine intake may also develop a tolerance against its physiological effects, thus a diuretic effect may not occur in caffeine-habituated (regular consumers) individuals. Abstaining from caffeine for just 4 days is sufficient for this tolerance to be lost (Fisher et al., 1986).
There is one particular study in 2014 that strongly supports hydration qualities of coffee when consumed in moderation by caffeine habituated males. Killer et al. showed that consuming 4 x 200ml coffee for 3 days to give a total of 4mg·kg·body weight of caffeine, did not influence total body weight, blood markers or 24h urine volume and markers, compared to the same quantities of water.
Caffeine content is not as high in tea as it is in coffee (see Figure 1), therefore a high as 9 cups per day is needed for a safe upper intake of 450mg caffeine. Scott et al. (2004) found no difference in hydration status between drinking tea or water when climbers were at altitude, where risk of dehydration is extremely high. Six cups of black tea per day also has no negative effects on hydration when compared to water (Ruxton et al., 2011).
Other reviews of the literature suggest there to be no detrimental effect on hydration up to 6mg·kg·body weight of caffeine per day – approx. 6 cups of coffee (Maughan et al., 2003; Ruxton et al., 2008).
Therefore, regular consumption of tea & coffee (3-6 cups per day) contributes to total fluid intake and should not be seen as a diuretic. Higher intake of caffeine (>6mg·kg), however, may cause slight dehydration by increasing urine volume, so just have 1 tsp. of coffee in your drink!
Figure 1. Caffeine content of drinks
Every day it seems there’s a new link between something we always thought was good for us and a life-threatening condition…so what’s the score with caffeine?
Well you’ll be happy to know that, so far, there is no knowledge of any adverse effects of moderate caffeine consumption in healthy populations. Known side-effects include insomnia, digestive discomfort, increased heart-rate and blood pressure, headaches, anxiety and restlessness, but this is due to large dosages and timings (insomnia by drinking before sleep).
However, there is one word in that sentence that determines people’s experiences with caffeine intake…moderate (moderation). Sadly people can, and have, died from caffeine overdoses, but this is rare. I actually heard of a case not so long ago, when Sports Science students were acting as subjects and were given a caffeine dosage in grams, instead of milligrams (Oops!). Luckily they survived.
On the brighter side, caffeine can offer many health benefits. Coffee and tea may also offer additional health benefits to caffeine alone, as they contain B-vitamins, phytochemicals and antioxidants.
Type 2 Diabetes
Van Dam et al. (2006) reported that 4 cups or more of coffee was better than just 1 cup per day for reducing the risk of type 2 diabetes in younger and middle aged women. There were also no differences between caffeinated and decaffeinated coffee, but tea consumption did not influence type 2 diabetes risk.
Another study showed 3 cups of tea or coffee reduced risk of type 2 diabetes by 42% in a prospective cohort of over 40,000 people (van Dieren et al., 2009).
Moderate coffee consumption is inversely associated with risk of heart failure, with the largest inverse association observed for consumption of 4 cups per day (Mostofsky et al., 2012). Likewise coffee consumption does not increase the long-term risk of coronary heart disease and may even lower it in women (Wu et al., 2009).
High consumers of tea may have a lowered risk of CV disease than low/non-consumers (Fardet et al., 2014), and may be attributed to tea’s flavonoid content and its impact on endothelial function, inflammation and cholesterol oxidation (Dwyer et al., 2013).
Tea consumption of 3 cups per day is also likely to reduce the incidence of stroke and mortality (Arab et al., 2013).
Cognitive function & dementia
Known for its short-term stimulatory effects on the brain, lifelong moderate consumption of caffeine/coffee may actually slow down physiological and age-related cognitive decline, and reduce the risk of Alzheimer’s disease. There have been mixed findings, with no definitive answer as to whether caffeine improves mental health later in life.
Drinking 3-5 cups per day during midlife may decrease the risk of dementia/Alzheimer’s disease by up to 65% (Eskelinen et al., 2009).
Middle aged and elderly populations may be more sensitive to the protective effects of caffeine on declining cognitive function by improving reaction time, attention span and feelings of well-being (Swift et al., 1988; Rees et al., 1999).
Caffeine and exercise performance
Caffeine is well researched as a nutritional strategy to enhance performance. To say that caffeine improves exercise performance is a simple answer to a complex question as there are many factors to consider. Without going into too much detail, I will outline the basic findings that support caffeine as an ergogenic aid in different sports.
Endurance exercise (60 minutes or longer)
- There is extensive evidence to suggest that caffeine ingestion improves endurance performance.
- More is not necessarily better, with 3-6g/kg body mass showing to be most effective (see Figure 2).
- Taking caffeine 30-45 mins before the event, during the event and in the late stages when fatigue starts to occur are all effective strategies, but recommendations are specific to the event, the athlete, and the practicalities of caffeine intake.
- Training low (fasted – before breakfast or glycogen depleted) performance may be rescued by caffeine ingestion, thus increasing training adaptations.
- Endurance performance is improved by delaying the onset of fatigue, which may be due to an increased fat utilisation and sparing of muscle carbohydrate (glycogen) stores, however this remains elusive.
High intensity sports (1-30 minutes)
- Caffeine ingestion 45-60 minutes prior to high-intensity sports events may improve performance.
- A lot of the research to support this has used doses of 6mg/kg body mass, however 3mg/kg may be equally as effective.
- Performance enhancement may be subject to caffeine’s stimulatory effects of the central nervous system, reducing feelings of perceived exertion and pain, increasing reaction time, alertness and mood, ultimately delaying fatigue.
Intermittent ‘stop and go’ sports (60-90 mins or longer)
- Individual and team based sports including tennis, football, rugby, hockey, cricket etc, have all shown improvements in performance following caffeine ingestion.
- 3mg/kg body mass appears to induce similar positive effects compared to 6mg/kg.
- Total distance covered, repeated high intensity bouts (e.g. sprints, jumps, scrums, tennis serves), skill, accuracy and cognition are all areas of performance that may be attributed to caffeine ingestion.
- Sports that rely heavily on skill and accuracy e.g. golf, shooting, archery, table tennis, which do not involve fatiguing exercise per se, but are conducted over long periods that likely cause feelings of mental and physical fatigue.
- Low-moderate doses of caffeine (1-2mg/kg) consumed both before and during an event may offer most beneficial effects, rather than high doses which may cause symptoms of jitters and anxiety.
- May improve golf putting & drive distance performance, archery target accuracy, overall mood and perceived feelings of energy and fatigue.
Strength and power sports (<20 seconds)
- Maximal efforts lasting just seconds include weight lifting, sprints, jumps and throws; common single activities for track and field athletics, sprint cyclists and also power lifters.
- The influence of caffeine for maximal strength (1 rep max) training appears to have minimal effect, however it’s more likely to enhance muscular endurance – increased reps to failure.
- This also applies to repeated maximal bouts of sprinting, cycling, throws (discus, shot-put) or jumps (long, high jump).
Figure 2. Exercise time to exhaustion. Data are mean data for exercise duration after placebo (0 mg/kg) or 3, 6, or 9mg/kg of caffeine. Letters a & b symbolise a significant difference from each other.
- Caffeine is not a diuretic in low-moderate doses, meaning up to 6 cups of tea or coffee per day can contribute to your total fluid intake without causing dehydration.
- This does not mean coffee/tea should replace water, but together can keep you hydrated.
- Regular caffeine consumption can develop a tolerance, therefore people who do not regularly drink tea or coffee may experience a slight diuretic effect.
- Avoid consuming late at night as it can disrupt sleep quality
- Caffeine tolerance can be lost after just 4 days abstinence.
- Regular caffeine/coffee/tea ingestion has many health benefits to fight against the development of cardiovascular diseases and type 2 diabetes, with some, but no conclusive evidence to suggest it improves cognitive health later in life.
- Caffeine as a pre-training stimulant can improve endurance, high-intensity and intermittent sport performance, with just 3mg/kg body mass being sufficient to maximise performance.
- 1-2mg/kg body mass may be sufficient to improve skill sports performance.
- It may also improve repeated high intensity bouts, but not necessarily maximal single (1RM) efforts.
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