A SUMMARY OF THE PHYSIOLOGICAL EFFECTS OF CAFFEINE

A SUMMARY OF THE PHYSIOLOGICAL EFFECTS OF CAFFEINE

Soon after drinking a cup of coffee, or tea or cola, caffeine is distributed throughout the body. As it is similar to substances normally present in the tissues, caffeine could affect all the systems of the body: nervous, cardiovascular, respiratory and so on. However, caffeine does not accumulate in the body, so its effects are short-lived and transitory.

Whether or not caffeine's effects are physiologically important (or even noticeable) depends on a number of factors. Every individual reacts differently to caffeine. For example, caffeine may stay in the body of pregnant women for up to three times as long as is usual in adults, whereas smokers eliminate caffeine twice as quickly as non-smokers. This may help to explain why women often feel more sensitive to coffee in the latter stages of pregnancy, or why heavy smokers are usually heavy coffee drinkers as well. Some of the effects of caffeine, such as those on the heart and blood vessels, are contradictory and have no net effect - others may only be noticeable when regular consumers suddenly cut out caffeine. The body can become habituated to caffeine so that regular users are less sensitive to the stimulant effects than others. In fact, people tend to regulate their coffee consumption according to their experience - as many cups of coffee in the morning as they find give a pleasant, stimulating effect - perhaps none a few hours before going to bed.

Of all the physiological effects of coffee, the best known is that it is a stimulant to the nervous system. One or two cups of coffee can make one feel more awake, alert and able to concentrate. Caffeine has been shown to counteract fatigue and restore flagging performance. However, in sensitive individuals, caffeine may delay the onset of sleep, decrease sleep time and even lower the subjective quality of the sleep. Caffeine has various effects on mood, ranging from pleasant stimulation and mood elevation to anxiety, nervousness and irritability, but these are transient and dose-related.

Other physiological effects of caffeine, in the short term, include increases in blood pressure, plasma catecholamines, plasma renin and serum free fatty acids; the production of urine and of gastric acid are also increased. Regular consumption in normal individuals rapidly leads to tolerance and has no adverse effects.

The vast bulk of scientific and epidemiological evidence points to the conclusion that normal, regular consumption of coffee and caffeine-containing beverages is not associated with heart or cardiovascular diseases, damage to the foetus, benign breast disease or cancer of any kind. Some people with irregular heartbeat syndromes may choose to drink decaffeinated coffee since caffeine has been known to precipitate arrythmias or ventricular premature beats, as do alcohol, exercise, stress and many drugs.

Standard reference

Evaluation of Caffeine Safety, a scientific status summary by the Institute of Food Technologists' Expert Panel on Food Safety and Nutrition, 1987. Food Technology, Institute of Food Technologists, Chicago, 41(6):105-113.June 1987

For further information on Coffee and Health, please see the Positively Coffee website at www.positivelycoffee.org.