CAFFEINE AND STRESS

CAFFEINE AND STRESS

Caffeine increases some of the normal stress responses because it increases the amount of adrenaline that is active in the body under stress­ful circumstances. Thus, it seems that caffeine users who find themselves under stress (or who use caffeine even more during stressful periods to work more effectively) may experience more of the effects that stress can produce. Adrenaline release increases blood pressure during stress, and the caffeine-induced rise adds to this. Thus, caffeine and stress together lead to greater bodily stress responses than either does alone.

CAFFEINE AND PANIC ATTACKS

In some people, caffeine can contribute to the experience of panic attacks, which generally come on suddenly and involve powerful feelings of threat and fear. The experience can be very debilitating for a brief period of time. It seems that caffeine is more likely to bring on panic attacks in people who have had them previously. However, relatively high doses of caffeine (greater than 700 milligrams) have been reported to lead to panic attacks in people who have never experienced them.

ENHANCEMENT OF PHYSICAL PERFORMANCE

Caffeine can slightly enhance physical endurance and delay fatigue asso­ciated with vigorous exercise in some people. One way that caffeine might accomplish this is by releasing fats into the blood for use as energy, enabling the body to conserve its other energy stores (in the form of stored sugars), thus allowing the athlete to sustain physical activity for a longer period of time. Caffeine may also help muscle performance during physical exercise, although the way this happens is not clear. What we do know is that caffeine dilates the bronchioles, making it easier for air to pass into the lungs. This would seem to have a beneficial effect on certain types of physical performance. Still, the most thorough studies of well-trained athletes are inconclusive. In some cases there appear to be performance-enhancing effects, and in others there are none. So the jury

remains out.

Two words of caution, though, for those who use caffeine for this pur­pose. Because caffeine causes an increased loss of water through urine production, a person exercising on caffeine may become dehydrated more rapidly during long periods of exercise such as distance running or cycling. This caution is particularly important for hot-weather exercisers. The other concern is the effects of caffeine on heart rate and heart rhythms. Strenuous exercise obviously stresses the heart, so a person with cardiovascular disease could experience problems while using caffeine to promote physical performance.

People who worry about their weight might be interested in the issue of fat metabolism. Products based on the supposed ability of caffeine and theophylline to "burn fat" include a theophylline cream placed on the market several years ago that was supposed to melt fat away. Just rub it on the offending fat pad! Unfortunately, the effectiveness of this treat­ment hasn't been established (one big problem is probably getting the theophylline through the skin and into the fat cells).

Likewise, there is tremendous interest in whether a combination of caf­feine and exercise can help to promote the burning of fat as fuel for weight loss. Fat cells really do have adenosine receptors, and xanthines really can cause a small release of stored fat, so some foods that include caffeine have been sold as fat burners. However, the scholarly research on these prod­ucts has demonstrated only small weight-loss effects. Coffee and its cous­ins may prove to be a useful part of weight-loss programs in the future, but at this point nothing "melts" fat except old-fashioned exercise and a healthy diet.

EFFECTS ON OTHER BODY PARTS

EFFECTS ON OTHER BODY PARTS

THE HEART

Caffeine affects the heart in two ways: it acts on brain centers that regu­late the cardiovascular system, and it acts directly on the heart. In people who are not tolerant to caffeine, a high dose (generally above 500 milli­grams—about four cups of strong coffee) can increase the heart rate by as much as ten to twenty beats per minute (from a baseline of eighty to ninety). In some, this dosage can result in brief periods of irregular heart­beat. However, in general, the morning cup of coffee does not have much effect on heart function in a healthy person.

There is controversy over the issue of caffeine and the gradual develop­ment of heart disease. At present, the scientific literature is inconsistent in its findings on the question of whether continued caffeine use increases the risk of heart disease or heart attack. One very large study of men found no relationship between coffee drinking and heart disease, while others have found an increased risk of heart attacks in coffee drinkers. Moderate caffeine consumption (up to 500 milligrams per day) probably does not place the user at significant risk for heart problems. Above that level, however, the risk of heart attack may increase. This would be particularly true for individuals with other risk factors for heart attack, such as smoking, being overweight, or having a family his­tory of heart disease.

Caffeine is also known to increase blood pressure, but generally this occurs with rather high doses and in people who already have difficulties with blood pressure regulation. For this reason, people with high blood pressure are often advised to avoid caffeine.

Cholesterol

An association between coffee drinking and cholesterol levels has been sus­pected for some time, yet it remains controversial. It is safe to say that the relationship has not been ruled out, but the picture remains unclear. One solid study has shown that five to six cups of coffee per day can increase LDI. cholesterol levels (this is the "bad" type of cholesterol as far as risk of heart disease is concerned) by 10 percent or more. This is not the case, however, if the coffee is prepared using a paper filter. While it is not clear exactly why filtered coffee fails to raise cholesterol levels, it is likely that oils from the cof­fee beans and other substances that promote fat buildup in the blood are trapped by the paper filter as the water passes over the coffee grounds.

THE KIDNEYS

The well-known bathroom break that follows the morning coffee is prob­ably caused both by a direct effect on the kidneys and by effects in the brain. There are adenosine receptors in the kidneys and caffeine acts on these, causing effects similar to those of diuretics, which increase urine production. Caffeine may also slow the release of an antidiuretic hormone from the brain that normally slows urine production.

THE DIGESTIVE SYSTEM

In coffee drinkers, the acids, oils, and caffeine can all irritate the stomach lining and promote secretion of acid, leading to gastritis (inflammation of the stomach). However, caffeine may not be the major villain, as decaf­feinated coffee has effects almost as great as caffeine-containing coffee. Although coffee was once blamed for ulcers, the primary cause of ulcers is now thought to be bacteria (Helicobacter pylori). Irritating agents like cof­fee and aspirin can contribute to the process by damaging the protective mucous lining of the stomach walls, but they probably don't cause ulcers on their own. In some individuals, caffeine in coffee can promote the reflux of stomach acid into the throat, resulting in painful heartburn.

THE RESPIRATORY SYSTEM

Caffeine and similar drugs have two quite separate effects on breathing.

The first was already mentioned: they stimulate the rate of breathing. The ophylline is sometimes used in treating premature infants with breathing problems. Xanthines also relax the smooth muscle in the bronchioles that take air into the lungs. This is very helpful in treating asthma, a disease in which breathing difficulties arise because these tubes constrict. Theophyl­line was used widely in the past to treat asthma and is still sometimes used today. However, concerns about side effects (restlessness, stomach upset) and the development of more effective treatments have diminished its use.

THE REPRODUCTIVE SYSTEM

Although studies in humans have not confirmed a link between caffeine consumption and birth defects, some studies report that babies born to women who used caffeine during pregnancy have lower birth weights. There is also some evidence that caffeine consumption (equivalent to more than one cup of coffee per day) can significantly reduce the chances of a woman becoming pregnant. Finally, there have been contradictory findings about the association between caffeine use and fibrocystic breast disease and eventual development of breast cancer. All of these associa­tions are questionable, and most studies do not support an association with the development of breast cancer.

THE EYES

Caffeine causes the tiny blood vessels in the eyes to constrict (become narrower) and thus decreases the flow of nutrients to the cells within the eyes and the clearing of waste products.

HOW CAFFEINE MOVES THROUGH THE BODY

HOW CAFFEINE MOVES THROUGH THE BODY

Caffeine is almost always taken by mouth, and so it is absorbed into the blood primarily through the linings of the stomach, small intestine, and large intestine. It is only slowly absorbed through the stomach, and so most absorption occurs at the next step along the gastrointestinal tract, the small intestine. However, once it reaches the intestines, virtually all of the caffeine that was ingested is absorbed. A given oral dose of caffeine takes full effect within thirty to sixty minutes, depending upon how much food is in the stomach and intestines and how concentrated the caf­feine is in the substance that contains it.

Caffeine is evenly distributed throughout the body, metabolized by the liver, and its breakdown products are excreted through the kidneys. The body eliminates it rather slowly, with the half-life of a given dose of caf­feine being approximately three hours. Thus, some of the caffeine that one consumes in the morning is still around well into the afternoon. A person who drinks several cups of coffee or caffeinated sodas across a morning or afternoon is adding on to an existing load of caffeine with each subse­quent drink and may end up feeling rather jittery by the end of the day.

HOW CAFFEINE WORKS

Caffeine is the best known of a class of compounds called xanthines (pro­nounced "zan-theenez"). Theophylline, another xanthine found in tea, is prescribed for breathing problems because it relaxes and opens breathing passages. However, there is so little of it in brewed tea that it exerts no significant stimulant effects in that form. In addition to a small amount of caffeine, chocolate contains theobromine, another xanthine, but one with far less potency than caffeine.

All the xanthines, including caffeine, have multiple actions. The major action is to block the action of a neurotransmitter/neuromodulator called adenosine, which is in the brain (more on this in the following). There are also adenosine receptors throughout the body, including those in blood vessels, fat cells, the heart, the kidneys, and many types of smooth mus­cle. These multiple actions create a confusing picture because the direct effects of caffeine on a system can be enhanced or suppressed by indirect effects on other systems.

EFFECTS ON THE BRAIN

Adenosine receptors, the main site of caffeine action, cause sedation when adenosine binds to them. Adenosine, a by-product of cellular metabolism, leaks out of cells. So, as neurons become more active, they produce more adenosine, and this provides a "brake" on all the neural activity—an ingenious self-regulation by the brain. Caffeine thus produces activation of brain activity by reducing the ability of adenosine to do As job. This is a good example of how a drug can produce an effect (in this case, central nervous system iCNSI stimulation) by inhibiting the action of a neu­rotransmitter that produces an inhibiting effect (a positive coming from two negatives). At moderate doses of around 200 milligrams (about what you get from one to two cups of strong coffee), electroencephalograph (EEG) studies indicate that the brain is aroused. Higher doses, in the range of 500 milligrams, increase heart rate and breathing. Activation of these centers also causes a constriction, or narrowing, of blood vessels in the brain (though outside the brain caffeine has a direct effect on blood vessels that does just the opposite—dilating, or widening, them).

Caffeine also lowers the amount of blood flow within the brain. It seems strange at first that a drug with such strong stimulant effects in the brain would actually decrease blood flow within the brain. But studies have shown that a dose of 250 milligrams (about what you get from two to three cups of coffee) reduces blood flow by nearly one-fourth in the gray matter of the brain (made up mostly of nerve cells) and by about one-fifth in the white matter through which fibers connect groups of nerve cells

into functioning circuits. The fact that caffeine has such powerful stimulant effects despite its decrease of cerebral blood flow underscores how powerful its stimulant effects really are. Further, the effects of a single dose of caffeine on cerebral blood flow were the same in heavy caffeine users and in light users, indicating that the blood flow effect is not one to

which people become tolerant.

People may develop a mild tolerance to some of the effects of caffeine, but most tolerant people can achieve an arousing effect by increasing the dose. The tolerance that develops to the brain-arousing effects of caffeine is less severe than the tolerance that develops to some of its effects on other parts of the body (see the following).

Dependence on caffeine can develop as well, as indicated by the occur­rence of withdrawal symptoms when caffeine intake is abruptly stopped. Between twelve and twenty-four hours after the last dose of caffeine, users generally experience headaches and fatigue that may persist for several days to a week but that are usually strongest during the first two days after quitting. Nonprescription pain relievers such as acetaminophen (Tylenol) or ibuprofen relieve the headaches, and moderate doses can be taken throughout the withdrawal period—just be careful to avoid taking pain medications that include caffeine Many people have found that they enjoy, and indeed rely on, the psy­chological effects of caffeine. While this wouldn't meet our definition of addiction, most caffeine users find the effects pleasant enough to continue using this drug. Therefore, those who decide to quit should also be pre­pared to give up those caffeine-aided feelings of alertness and mild eupho­ria, which may have become a very regular and important part of each day. A related issue is that people who drink caffeinated beverages often do so at the same or similar times of day. In that way the drinking itself may become a part of important daily rituals. It is important to anticipate that changing those rituals may be difficult as well.