Reviewed by Patricia Rosen. M.D.
Introduction Coffee was first discovered over 1000 years ago although it has been around and used by humans since the Stone Age. People noted the affects on animals and used it by chewing on seed, bark or leaves of certain plants to gain the effects of elevated mood and decreased fatigue. It is thought to be the most widely used psychostimulant in the world. Sources estimate 120,000 tons of caffeine is consumed annually. 90% of adults in North America consume some caffeine daily. Just witness the explosion of coffee vendors on every street corner and the waiting lines at your local Starbucks.
Caffeine was discovered by a German chemist, Friedrich Ferdinand Runge, in 1819. Caffeine is also called guaranine which is found in guarana, mateine when found in mate and theine when found in tea but all of these are synonyms for the same compound, trimethylxanthine.
It is found in many plants and acts as a natural pesticide that paralyzes and kills certain insects feeding on the plants. Note that in many natural sources of caffeine other compounds are present that have other effects such as theophylline and theobromine. In humans, caffeine is used as a central nervous system stimulant and is most often obtained from coffee.
Caffeine continues to be one of the most studied and consumed ergogenic substances. Researchers are constantly re-designing studies to get a clearer indication of how caffeine improves performance. Each year new studies are published on the effects of caffeine on endurance activities. Everyone knows that a strong cup of Java gives you alertness and sense of extra energy. Does the caffeine simply make you want to run a marathon or does the caffeine actually help you finish it faster? And can it do so safely? and how much is safe? Some of the more recent reviews will be discussed in this newsletter.
Historically, athletes have used caffeine to enhance their performance. Prior to 2004, caffeine was banned by the US Olympic Committee, World Anti-Doping Association (WADA) and US Anti-doping association. The level at which caffeine was banned was 12 mcg/ml in urine, which requires about 1,200 mg of pure caffeine or 8 cups of strong coffee. However, this decision was reversed in 2004, allowing the use of caffeine in elite level sports. Fortunately, the dose required to elicit an ergogenic effect is much less than the level banned thus to gain benefit an athlete does not have to suffer toxicity.
There is general agreement that:
1. Caffeine does not appear to benefit short term, high intensity exercise
2. Caffeine can enhance performance in endurance sports.
Caffeine acts through multiple mechanisms by acting on receptors and channels in the cell membrane as well as acting on calcium and cyclic AMP pathways. The principal mode of action is as an agonist at adenosine receptors in the brain as its structure is similar to adenosine. This results increased activity of dopamine. Caffeine also increases release of acetylcholine in the prefrontal nucleus resulting in increased wakefulness and locomotor activity. Caffeine also increases levels of epinephrine and adrenaline as well as levels of serotonin, resulting n positive changes in mood.
Caffeine is a competitive inhibitor of cAMP-phosphodiesterase thus resulting in an increase in cAMP in cells. Thus caffeine intensifies and prolongs the effect of epinephrine. This also increases activation of protein kinase A which is important in glucose syntheses.
Metabolites of caffeine contribute to caffeine’s effects. Theobromine is a vasodilator and increases oxygen and nutrient flow to the brain and to the muscles. Theophylline acts as a smooth muscle relaxant and acts to relax the bronchioles and is a chronotrope and inotrope affecting an increase in heart rate and efficiency. The third metabolite, paraxanthine, increases lipolysis which releases glycerol and fatty acids into the blood to be used as a fuel by muscles.
So in plain words what this means for the athlete is that caffeine in moderate amounts improves alertness, and increases the use of fat as fuel. At the same time, caffeine opens the bronchioles and improves cardiac efficiency. Caffeine use can thus spare glycogen which is the principal fuel for muscles. This means that exercise can be prolonged as glycogen is the principal fuel for muscles. In fact, caffeine has been shown to decrease glycogen utilization by as much as 50%. Thus more glycogen is available at the later stages of exercise. Subjects of experimental studies were able to exercise longer before exhaustion would occur by enhancing the use of fat as fuel and preserving glycogen. The critical period when glycogen sparing occurs is during the first 15 minutes of exercise. Pre-race caffeine may thus be beneficial in a longer a race.
There is some controversy surrounding the lifted ban since caffeine does have some ergogenic properties but it can also be dangerous if abused. Back to running the marathon: caffeine can help you run it faster, but only if done correctly, so let’s talk about who can benefit from caffeine and how it can be properly used.
Notes to consider:
- Caffeine is often mistakenly classified as a diuretic. Diuresis (elimination of water from the body) can complicate an individual’s water balance, which determines how efficient he/she will perform by decreasing stroke volume and the amount of blood delivered with each heart beat. However, research performed on trained athletes has NOT FOUND caffeine to cause a diuretic effect. See Diuretic Effects of Caffeine for more details.
- Caffeine has thermogenic properties. This means ingestion of caffeine can raise your core body temperature. Recent research has not shown this to be true (Roti, Miller). Two separate placebo -controlled studies have shown no difference in urinary or plasma electrolytes, thermoregulatory variables or cardiovascular variables, even in warm, humid environments.
- Because our body has the ability to build a tolerance to caffeine, it has been suggested to athletes to abstain from caffeine use days/weeks prior to a race. The theory behind this method is to allow the body to become accustomed to not having caffeine and with reintroduction the ergogenic effect will be increased. However, research indicates that the body will respond to the withdrawal from caffeine experienced overnight as much as abstaining from caffeine over prolonged periods of time. The half life (time of clearance) of caffeine in the body is 6 hours. A study by Roti et al. showed improved exercise heat tolerance in a group chronically receiving caffeine compared to placebo.
Recently published research supporting use of caffeine with trained athletes:
Kovacs et al. (1998) studied well-trained cyclists. The results of this study support the use of caffeine during competition to improve performance. In this study, 15 cyclists ingested different levels of caffeine in addition to a carbohydrate-electrolyte drink during a time trial. The highest caffeine doses (225 and 320 mg) resulted in a 5% increase in power relative to control trials without caffeine (308 + 9 W and 309 + 10W versus 295 + 9W, respectively). The amount of caffeine ingested during this study was relatively small, and yielded caffeine concentrations in the urine of less than 5 mg/L for the participants.
Another recent study by Cox et al. (2002) supported the use of caffeine both before and during cycling performance. This study involved a cycling time trial which occurred after 2 hours of steady state cycling at 70% of VO2max. Several different patterns of caffeine ingestion were utilized, including different levels before and during the trial. None of the methods caused an increase in caffeine concentration in the urine to exceed 12ug/ml. These results also demonstrate that ingestion of 1-3 mg/kg of caffeine produced the same level of performance enhancement (~3%) as did the higher levels of caffeine intake (6 mg/kg).
Yeo et al. (2005) published a recent study that looked at the effects of caffeine ingestion on carbohydrate oxidation. Eight male cyclists exercised for 120 min on three separate occasions. During exercise, cyclists ingested either a 5.8% glucose solution (Glu; 48 g/h), 5.8% glucose solution with caffeine (Glu+Caf, 48 g/h + 5 mg·kg·h-1), or plain water (Wat). Average exogenous CHO oxidation over the 90- to 120-min period was 26% higher (p < 0.05) in Glu+Caf (0.72 +/- 0.04 g/min) compared with Glu (0.57 +/- 0.04 g/min). Total CHO oxidation rates were higher (p < 0.05) in the CHO ingestion trials compared with Wat, but they were highest when Glu+Caf was ingested (1.21 +/- 0.37, 1.84 +/- 0.14, and 2.47 +/- 0.23 g/min for Wat, Glu, and Glu+Caf, respectively; p < 0.05). There was also a trend (P = 0.082) toward an increased endogenous CHO oxidation with Glu+Caf (1.81 +/- 0.22 g/min vs. 1.27 +/- 0.13 g/min for Glu and 1.12 +/- 0.37 g/min for Wat). In conclusion, compared with glucose alone, 5 mg/kg caffeine (approximately 350mg caffeine for a 150lb athlete) co ingested with glucose increases exogenous CHO oxidation, possibly as a result of an enhanced intestinal absorption.
Doherty et al, (2005) recent meta-analysis of the use of caffeine ingestion on rate of perceived exertion (RPE) supports the use of caffeine as an ergogenic aid. Twenty-one studies were reviewed. In comparison to placebo, caffeine reduced RPE during exercise by 5.6% (95% CI). These values were significantly greater (p<0.05) than RPE obtained at the end of exercise (RPE % change, 0.01%; 95%). In addition, caffeine improved exercise performance by 11.2% (95% CI; 4.6 17.8%). Regression analysis revealed that RPE obtained during exercise could account for 29% of the variance in the improvement in exercise performance. These results demonstrate that caffeine reduces RPE during exercise, which may partly explain the subsequent ergogenic effects of caffeine on performance.
In a 2004 study, Doherty et al. investigated the effects of caffeine ingestion on a ‘preloaded’ protocol that involved cycling for 2 min at a constant rate of 100% maximal power output immediately followed by a 1-min ‘all-out’ effort. Eleven male cyclists completed a ramp test to measure maximal power output. On two other occasions, the participants ingested caffeine (5 mg·kg) or placebo. Ratings of perceived exertion (RPE; 6-20 Borg scale) were lower in the caffeine trial by approximately 1 RPE point at 30, 60 and 120 s during the constant rate phase of the preloaded test (p <0.05). The mean power output during the all-out effort was increased following caffeine ingestion compared with placebo (794+/-164 vs. 750+/-163 W; p=0.05). Blood lactate concentration 4, 5 and 6 min after exercise was also significantly higher by approximately 1 mmol in the caffeine trial (p <0.05). These results suggest that high-intensity cycling performance can be increased following moderate caffeine ingestion and that this improvement may be related to a reduction in RPE and an elevation in blood lactate concentration.
McClellan and Bell (2004) looked at the ergogenic role of ingesting coffee (COF) prior to the subsequent ingestion of anhydrous caffeine (CAF). Thirteen subjects performed 6 rides to exhaustion at 80 % VO2max 1.5 h after ingesting combinations of COF, decaffeinated coffee (DECOF), CAF, or placebo. Time to exhaustion was significantly greater for all trials with CAF compared to placebo. In conclusion, the prior consumption of COF did not alter the ergogenic effect of the subsequent ingestion of anhydrous CAF.
Brinbaum et al. (2004) observed the physiological effects of caffeine on cross-country runners during submaximal exercise. Ten college-age subjects (5 women; 5 men) volunteered to participate in this study. After completing a VO2max test, each subject completed 2 30-minute runs at 70% VO2max on the treadmill, 1 after ingesting caffeine and the other after ingesting a placebo. Tidal volume (TV), alveolar ventilation (VA), and rating of perceived exertion (RPE) were significantly different (p < 0.05) between treatment and control groups. The results suggest that the ingestion of caffeine at 7 mg·kg of body weight prior to submaximal running might provide a modest ergogenic effect via improved respiratory efficiency and psychological lift.
LATEST CAFFEINE RECOMMENDATIONSAN ERGOGENIC AID
|NOTE: CAFFEINE HAS BEEN REMOVED FROM WORLD ANTI-DOPING AGENCY’S (WADA) 2004 LIST OF PROHIBITED SUBSTANCES AND METHODS|
It was previously thought that caffeine’s ergogenic effect was limited to endurance events lasting greater than 2 hours. Based on the latest clinical research, evidence now suggests that individual’s participating in short bouts of exercise may also benefit from the use of caffeine. The mechanism of action appears to be quite different and varied depending on the length of activity. There are very few controlled studies looking at the effects of caffeine on endurance events lasting longer than 2 hours.
For low to moderate intensity activities
Caffeine has been shown to stimulate the use of stored fat (free fatty acids). This in-turn spares carbohydrates and allows athletes to exercise longer.
For high Intensity activities
Caffeine improves the athlete’s rate of perceived exertion and oxidation of ingested carbohydrates as well as allowing for higher lactate levels to be reached. These physiological changes allow the athlete to push a little harder and may elicit improved performance.
The use of caffeine is ubiquitous. There does appear to be significant performance benefits. Caffeine is not a banned substance, although a survey of 140 competitors at the 2005 Ironman Triathlon World Championships revealed only 72% of the athletes were aware of this. 89% of athletes indicated they planned on using caffeine either before or during competition. Levels of plasma caffeine taken immediately post race indicated that athletes typically finish with quantities of caffeine that have been shown to improve endurance performance (i.e., approximately 20 micromol/L or a dose of > or = 3 mg/kg body weight). (Desbrow)
Using caffeine as an ergogenic aid should be done with caution. Caffeine’s stimulatory effect on the central nervous system can pose harm to individuals at risk. On the day of your event consume caffeine prior to your event in a dose similar to what you are used to. If you choose to use caffeine as an ergogenic aid, do not consume more than 3 – 9 mg·kg body weight (that’s 210mg to 630mg for a 150 lb athlete). Excess caffeine can cause anxiety, irritability, delirium and hallucinations in high doses but certainly can make you jittery and give you stomach difficulty. Be aware of the possible side effects. Athletes should assess how their bodies respond to caffeine prior to the day of the race to determine if the use if beneficial for them. WADA’s removal of caffeine from its banned substance list does raise some concerns. If abused, caffeine can be detrimental and dangerous. Caffeine’s actions excitatory effects can cause injury if the dose is too high. We strongly urge all athletes wanting to use caffeine to do so cautiously.
Typical Caffeine amounts:
Caffeine tablet: 100 mg -200mg
Excedrin tablet: 65 mg
Chocolate: 1 bar equals 31 mg
Coffee brewed: 7 oz equals 80-135 mg
Coffee drip: 7 oz equals 115-175 mg
Coffee decaffeinated: 7 oz equals 5 mg
Coffee espresso: 2 oz equals 100 mg
Tea (leaf): 6 oz equals 50 mg
Tea (green) 177 ml equals 30 mg
Coca-cola classic: 12 oz equals 34 mg
Mountain Dew: 12 oz equals 54.5 mg
Jolt cola: 23.5 oz equals 150 mg
Red Bull: 8.2 oz equals 80 mg
Wired X 344: 16 oz equals 344 mg
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