Dr. John William Daly, one of the most respected researchers on the pharmacology of caffeine, states in his 1993 review paper “The Mechanism of Action of Caffeine”83 that, in addition to its effects on the cardiovascular, respiratory, renal, and central nervous systems, caffeine affects adipose (fat) tissue by stimulating lipolysis, that is, by increasing the catabolism, or burning, of fat. Additionally, caffeine partially blocks the effect of adenosine and adenosine analogs, neurotransmitters that inhibit lipolysis. In other words, caffeine enables your body to burn fat faster and might help you to lose weight.
There is some clinical evidence of this effect. People undertaking exercise studies under controlled conditions demonstrate more weight loss if their exercise was preceded by a very hefty dose of caffeine. Caffeine increases the level of circulating fatty acids, so-called free fatty acids, or FFA, released from adipose tissue. Between one and two hours after consumption, or according to other studies, three to four hours or more after consumption, caffeine has been shown, under certain conditions, to increase the oxidation of these as fuel and hence to enhance fat oxidation. Caffeine has been used for years by runners and endurance athletes to improve performance, presumably by enhancing fatty acid metabolism. It seems effective in those who are not habitual users. Some studies suggest that this effect is most pronounced during longduration low-intensity exercise, where lipids play a more important role in energy production, and that the effects are most noticeable in persons who are not highly trained athletes.
Caffeine may also work in other ways to help weight loss. It increases basal metabolic rate and resting metabolic rate, in both lean and obese subjects, by as much as 15 percent, and keeps these rates elevated for at least two hours after ingestion.84 Additionally, there is ample anecdotal evidence that caffeine, like other stimulants, such as amphetamine and cocaine, is an appetite suppressant.
The practical question remains: Can caffeine be an effective aid to weight loss, and if so, under what conditions and to what degree will it augment the efforts of diet and exercise in shedding pounds? As with so many questions about caffeine and health, the answer seems to be a combination of “it depends” and “nobody knows.” There have been many studies of the interaction of caffeine and exercise and of the effects of caffeine on levels of FFA and fat oxidation. The conclusions are apparently contradictory, providing support for just about any combination of conclusions you might choose to argue. The effects of caffeine on energy output, endurance, and fat metabolism vary widely on account of many factors: the complexity of the human system, the variations in how much caffeine is consumed, how long before the trial it is consumed, how long the exercise is continued, the physical condition of the subject, the tolerance of the subject to caffeine, and which muscles are being used in the exercise. Psychogenic effects may also be important: People may not perceive themselves as growing tired when they have ingested caffeine, and therefore they may continue their efforts longer. More carefully designed studies are needed to define the contributions of this slew of confounders. Meanwhile, there is good evidence that caffeine can help at least some people doing some exercises to do them longer and burn more fat while doing them.
Caffeine and Exercise and Athletic Performance: Is Caffeine an Ergogenic Aid?
There is a widespread conviction among many athletes and sportsmen that caffeine boosts performance in terms of endurance and energy output, and that, in short, using caffeine helps you to increase your speed and capacity to lift weights, and in general to excel in athletic pursuits. Many long-distance cyclists, runners, and crosscountry skiers use caffeine during competition. Even racehorses are sometimes doped with and tested for caffeine.
The belief in the power of caffeine to augment athletic capacity is reflected in a 1962 decision by the International Olympic Committee (IOC) to restrict caffeine use by participants in the games to a urinary concentration of 15 mg/litre. The uncertainty about the effects of caffeine is reflected in the IOC’s repeated flip-flops over whether to continue restricting it and, if so, how much to allow in the serum levels of participants. Subsequent to the initial ban, the IOC dropped caffeine from its list of restricted drugs, and then, in 1984, restored it. Athletes alleged that, because of wide variations in the metabolism of caffeine among individuals, consumption of as little as 350 mg had caused some participants to nearly flunk the test. Because readings above the allowable level are regarded as deliberate attempts to “dope” the athlete, a 1988 study by researcher van der Merwe attempted to determine how much caffeine would put a competitor out of action. He administered varying amounts of caffeine by serving coffee, tea, and soft drinks to nine healthy subjects, within a fifteen-minute period. Although the doses ranged up to 1,000 mg, as much as in ten cups of coffee, no urinary levels were found to exceed 14 mg/litre, as measured three hours after ingestion. Consistent with other researchers, van der Merwe found that about 75 to 90 percent of the ingested caffeine appeared in the urine and the observed concentrations were independent of the dietary source. He concluded that it was impossible to flunk the IOC test as a result of the ordinary consumption of caffeinated beverages and that any athlete who failed to pass should be presumed to have resorted to caffeine to enhance his performance.85 Although a number of athletes have run into trouble over their urinary levels of caffeine, so far the IOC itself has disqualified only one participant on this account, an Australian pentathlon competitor in the Seoul Olympics in l988.86
Interest in caffeine’s benefits to exercise increased in the late 1970s after studies from the Human Performance Laboratory at Ball State University suggested that 200 mg of caffeine exerted a significant effect on an athlete’s endurance. Other studies have failed to confirm this conclusion, and some have suggested that the observed improvements were a consequence of a placebo effect. Determining the answer comes down to evaluating whether caffeine has ergogenic effects—that is, whether it can improve aerobic performance or the capacity of the body for physical work.
The body gets the energy needed to power muscles in at least three different ways, depending on whether the energy expenditure is of short, moderate, or extended duration. Energy is also burned differently by muscles of different sizes. For example, the large muscles of the legs, used in treadmill walking, burn energy differently from the smaller leg muscles, primarily used in cycling, which may be more responsive to the benefits of lipid mobilization. In addition, people in excellent physical condition, such as athletes, burn energy differently from people in a more ordinary state of dilapidation. Other variables include caffeine dose, pre-exercise food consumption, and individual variations in response and tolerance. All of these factors confuse our attempts to make sense out of the apparently inconsistent research findings about the effects of caffeine on energy output, endurance, and weight loss.
The basic theory underlying claims that caffeine can improve athletic performance is based on three assertions. The first is its ability to increase the efficiency with which the body burns fat, already alluded to in the weight-loss discussion above. This is considered the primary source of caffeine’s power to act as an ergogenic aid and to increase endurance for intense exercise, especially when duration approaches or exceeds one hour. Increased FFA mobilization delays the depletion of glycogen by encouraging the muscles to use fat as fuel, making the spared glycogen available to delay exhaustion, especially at high exercise intensities for which glycogen sparing is critical. This effect is minimized at exercise below the anaerobic threshold, that is, in low-intensity exercise, and experiments have shown that ingesting 400 mg of caffeine before such exercise did not affect either FFA or carbohydrate utilization.
The second claim is caffeine’s ability to reduce the rate of glycogen consumption— that is, it increases the efficiency with which the body burns sugars. Because glycogen is a primary source of energy for exercise, exhaustion occurs and exercise intensity must generally be reduced once glycogen has been depleted. This glycogen-sparing effect is greatest in the f
irst fifteen minutes of exercise, during which glycogen utilization declines as much as 50 percent. The saved glycogen remains available during the later stages of exercise with the result that the athlete can continue longer before exhaustion occurs.
The third assertion is caffeine’s power to lower the rate of perceived exertion (RPE)—that is, to reduce our sense of fatigue. Some studies have shown that when athletes are asked to rate how hard they are working, some report significantly less exertion after consuming caffeine.
The popularity of sports snacks is increasing as athletes and exercisers search for anything that can give them an edge. When the National Academy of Sciences evaluated six purported performance boosters for the U.S. Army, the only ones they endorsed as effective were those that contained carbohydrates or caffeine. Although other ingredients might show promise, no claims can be supported without further research. These conclusions have been bolstered by studies, such as the one which demonstrated that the intake of sucrose, with or without caffeine, improved running time and distance from about forty minutes and six miles to about fifty-five minutes and nine miles.87 Other studies showed that consumption of about 900 mg of caffeine, which produce urinary levels just within the limits of the IOC, increased endurance time from fifty to more than seventy minutes.
In their quest for a chemical means of improving performance, many turn to over-the-counter combination products that contain both caffeine and ephedrine. An example of such a product is Formula One, a nostrum touted by its manufacturers as the “world’s first scientifically valid, gimmick free approach to weight management,” which contains a combination of ma-huang and cola nut. This combination was recently banned by the FDA in a new ruling that outlawed all products containing a combination of caffeine and ephedrine, stating that they can cause “severe injury or death in some people who consume them.”
We should be mindful of a range of possible impairments in performance that may counterbalance the possible improvements in output that may be obtained with caffeine. By increasing digestive secretions, caffeine may cause stomach discomfort and thereby impede performance. And perhaps more important, because caffeine is a diuretic, it may promote excess urination, which in turn could lead to dehydration, one of the primary problems for athletes, especially endurance athletes, because the fatigue experienced as a result of dehydration is indistinguishable from the normal fatigue of hard training. Excessive urination can also cause a loss of vitamins and minerals essential to peak athletic performance, although it must be noted that some studies have found no effect from caffeine on either fluid balance or thermoregulation during exercise. In light of such considerations, however, athletes should be mindful of the possibility that intestinal problems or dehydration might create an acute disadvantage in the middle of an athletic event which more than offsets any earlier advantage.
In summary, the effects of caffeine as an athletic performance booster are still uncertain. It remains for future researchers to satisfactorily evaluate caffeine’s effect on an ordinary activity such as walking, by designing an experiment comparing the effect of a range of caffeine doses on well-hydrated, moderately trained subjects walking in controlled environments for an extended time. Such low-intensity exercise studies would help determine caffeine’s part in FFA mobilization.88
16
thinking over caffeine
Cognition, Learning, and Emotional Well-Being
BACON says, Coffee “comforts the head and heart, and helps digestion”; Dr. WILLIS says, “being daily drank, it wonderfully clears and enlightens each part of the soul, and disperses all the clouds of every function.” The celebrated Doctor HARVEY used it often; VOLTAIRE lived almost on it; and the learned and sedentary of every country have recourse to it, to refresh the brain, oppressed by study and contemplation.
—Benjamin Moseley, M.D., A Treatise Concerning the Properties and Effects of Coffee, 1785
The saying goes, “You can’t be too rich or too thin,” to which perhaps could be added, “or too smart,” because, even if each man is correct about how bright he conceives himself to be, he would find it still better to be even a bit sharper. How far would you go to acquire, for example, a drug that would enable you to perform better on an IQ test, an SAT test, or a Bar examination? Or one that would help you to prepare your taxes or balance your checkbook more accurately, solve chess problems or crossword puzzles more readily, make better investments, or program a computer with more acuity, or even drive home more safely? Surprisingly, you might not have to go very far, because caffeine, in many ways, is a “smart pill” that can do just those things.
As demonstrated by scientific evidence and common experience, caffeine is a rare and wonderful substance that safely improves many mental functions, including alertness, memory, learning, and cognition. As early as 1933, one researcher analyzed the effects of caffeine on solving more than 250 chess problems, comparing performance of test subjects with and without caffeine. He observed a consistently remarkable improvement in performance with caffeine.1 Such improvements were reflected in a 1960s advertising campaign that dubbed coffee “The Think Drink.”
However, as to what the nature of this improvement may be or how great its extent, there is little agreement anywhere. Some people are convinced that they can’t think clearly or precisely without caffeine, while others say it makes them jittery and error prone. Naturally, behavioral scientists have been eager to discover the secret of caffeine’s ability to improve the brain’s information processing. Two complementary hypotheses explaining this remarkable power are supported by experimental data. The first hypothesis, sometimes called the “non-specific energetic” theory, attributes caffeine’s enhancement of mental functions to a generalized energizing effect. The second hypothesis, sometimes called the “specific cognitive” theory, attributes these enhancements to specific effects on brain or neural activity. Finally, a “cognitive-energetic” theory, combining the two, has also been formulated and may offer the most complete and best-integrated elucidation of the phenomena.
J.E.Barmack, in a paper published in the Journal of Experimental Psychology in 1940, was one of the first to advance the non-specific energetic theory. Barmack recognized the possibility that caffeine’s overall antihypnotic and antifatigue properties could be part of the story, but, observing that caffeine increased the rate at which people can add numbers, advanced the notion that caffeine acts non-specifically on “some central process or processes concerned with alertness” that “allay the development of a bored attitude to a task.”2 This idea is supported by many studies of continuous performance, over a period of a half-hour or more of what experimental psychologists call a “vigilance task,” one that requires prolonged attention and responsiveness but little physical activity. In real life, caffeine improves long-term performance on vigilance tasks such as solving arithmetic problems, driving a car, or flying an airplane. Its effects are most apparent when people have been working at their tasks for some time and are minimal when tasks are just begun. When people are allowed to take breaks to alleviate boredom and fatigue, no significant benefit from using caffeine is observed. These findings, based solely on studies of vigilance tasks, apparently confirm Barmack’s theory, that caffeine acts by “refreshing” a fatigued person, so that the enhancing effects of caffeine on long-term performance will obtain on any task that is performed repetitively, monotonously, and requires continuous attention.3
The specific cognitive theory, championed by H.Nash in his 1962 book Alcohol and Caffeine,4 asserts that caffeine acts directly on “specific neural capacities” that are intrinsic to a given task and that it enhances performance on these tasks irrespective of whether a person is fatigued. This idea was suggested to Nash by his examination of performances of several different short-term tasks, some of which exhibited improvement after caffeine was ingested, while others remained unaffected. Nash argues that the benefits of caffeine on performance depend not on an improvement in general energy levels, as Barmack
had asserted, but instead on specific benefits related to the nature of the task at hand. Abandoning the metaphor of the organism as an energy system, Nash relied on another metaphor, one that became and remains the most generally accepted in cognitive psychology today: that of the human organism as an information-processing system. He observed improvement in the performance of a number of tasks, such as adding numbers, immediate recall, and word fluency. These benefits were realized even on brief tests administered when the subjects were rested and alert, and neither fatigued nor bored. In contrast, he found no improvement in tests of abstract reasoning, using language, deduction, estimating time intervals, or spotting arithmetic mistakes. The overall conclusion from such studies has been that caffeine “facilitates the speed, but not the memory, component of the task.”
If Barmack’s non-specific energizing theory is correct, we should expect caffeine to improve cognitive performance only when a person has become bored or tired. If Nash’s specific cognitive theory is correct, we should expect an improvement even when a person is rested and alert to start with, but this improvement would be observed only in some tasks and not others. However, because these theories are complementary rather than inconsistent, which is to say, they could both be true at the same time, we must also consider the syncretic hypothesis of A.F.Sanders, who argues that the improvements in mental capacity caused by caffeine are a function of both the energy level of the subject and the cognitive nature and demands of the task.5 Aiming to unite the energetic and cognitive models of human information processing, Sanders published his idea in 1983 that caffeine’s effect on performance is best understood as a function of both the energetic state of the person and the cognitive requirements of the task.
Unfortunately, even with the advancement of Sanders’ cognitive-energetic theory, the scientific community remains far from a complete and consistent explanation of caffeine’s sometimes apparently paradoxical effects on human performance. For example, an adverse effect has been observed on the attempt to repeat numbers backward, while a beneficial effect has been observed on the attempt to repeat them in their original order. In addition, caffeine impaired some factors of cognitive intelligence, while improving those related to speed. In other cases, caffeine had a deleterious effect on a given task until that task was practiced, whereupon the use of caffeine resulted in an improvement.6 Another troubling inconsistency is the low level of test-retest reliability. That is, the results of studies of caffeine’s effects, particularly on the performance of complex tasks, vary widely, forcing us to wonder which conclusions are the correct ones.7
The World of Caffeine Page 43