The Power Of Caffeine
THE PREVAILING THEORY of why caffeine increases alertness took shape only in the early 1970s. The theory holds that caffeine interferes with the depressant effects of adenosine, which is one of the chemicals that the body makes to control neural activity~ Adenosine triggers a series of slowing effects: it depresses mood and alertness, lowers the need to urinate and slows gastric secretion and respiration. After it is released by nerve endings in the brain, adenosine must reach receptors on the surface of certain brain cells in order to work. Caffeine, the theory has it, acts as an adenosine impostor. Molecules of caffeine counterfeit molecules of adenosine, locking into the adenosine receptors on brain cells. They fool the body into thinking that adenosine is circulating, but they produce no depressive effect of their own.
Caffeine speeds you up, then, by not slowing you down. Its effects are the opposite of what adenosine does: it makes you feel brighter and more alert, increases gastric secretion, makes you urinate more and stimulates respiration.
Proponents of caffeine speak of its ability to increase vigilance and heighten the ability to perform various tasks. Its effects are most pronounced, how- ever, when compared with performance levels that are low because of fatigue, boredom or caffeine abstinence. Too, its effects seem to vary by personality type. For example, caffeine appears to help extroverts keep performing vigilance tasks better than introverts, who can evidently plow through such tasks unassisted.
Despite the generations of writers who have thought that coffee helped them think more clearly, caffeine seems only to increase intellectual speed, not intellectual power. Subjects in experiments do things like read and fill out crossword puzzles faster-but not, unfortunately, more accurately.
Caffeine quickens reaction time and can enhance both hand-eye coordination and the capacity of muscles to work. This boost to overall endurance has led to its use by cyclists and runners. But caffeine also has a diuretic effect, increasing frequency of urination. Caffeinated drinks are thus dehydrating, good for neither athletes nor flyers: dehydration is one of the worst problems of air travel and a prime cause of jet-lag.
Caffeine speeds up the metabolism and makes you burn calories faster, although not so much faster that it will help you lose weight. Its inclusion in over-the-counter diet pills in place of prescription-only amphetamines ("speed") seems to be largely ineffective. Amphetamines, which diminish appetite, work differently than caffeine does on the brain.
This general quickening does not mean that coffee can sober you up - either black or with milk. Your motor functions will be just as impaired by alcohol as they were minutes before you downed that cup of coffee, and even if you feel more awake, you're just as dangerous a driver. Similarly, caffeine does not counteract the effects of phenobarbital and other barbiturates. It does, however, help reverse the impairment of cognitive activity caused by benzodiazepines, the compounds that are the basis of Valium and many other tranquilizers. This reversal affects how you think as opposed to how fast you react. If you are taking a muscle relaxant or tranquilizer that you think might be one of these compounds, ask your doctor; he or she will probably advise you not to defeat the effects of the drug by drinking coffee.
Some researchers speculate that a similar restorative effect on cognitive activity might take place in the interaction between caffeine and alcohol, but no one yet knows. Remember, though, that the question is whether caffeine can help you think more clearly after you have drunk alcohol - not whether it will improve your reflexes. No one imagines that coffee can make you a safer driver after you've been drinking.
Besides being a self-prescribed antidepressant and alertness drug, caffeine has been shown to be useful to people with asthma, since it works as a bronchodilator, meaning that it widens the air passages in the lungs and eases breathing. It might even be something of an aphrodisiac, if the results of a University of Michigan study can be generally applied: the study showed that older subjects were more likely to be sexually active if they were coffee drinkers than if they were not.