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.