Coffee and tea contain many substances, of which people chiefly think of caffeine. Going by the chemical name of trimethylxanthinem, it is the most widely consumed pharmacologically active substance in the world.
Caffeine's role in the human body is mostly to increase alertness by stimulating the central nervous system. An average-sized cup (150ml) of roasted ground coffee contains around 85mg of caffeine while instant coffee contains 60mg, decaf coffee 3mg, bag tea 30mg, instant tea 20mg, and cocoa or hot chocolate 4 mg.
The effect of caffeine on the cardiovascular system, especially the heart, has long been studied extensively. The heart acts as a pump and the heart muscle, or myocardium, has the unique property of automaticity, that is, it is able to contract and relax in an automatic fashion. It also has the nerve that controls the rhythm of the beating heart.
The valves in the hart ensure that blood flows in the correct direction. The myocardium and the nerves respond to a variety of physiological conditions such as emotions and physical exercise via chemical and hormonal transmitters, which stimulate the receptors on the heart. Externally introduced chemicals via injections or by mouth act the same way on the receptors and affect the function of the heart.
The effect of coffee on the heart has been studied in several aspects. First, can coffee induce coronary artery disease? Coronary artery disease is a condition whereby the wall of the artery becomes damaged owing to accumulation of fat and cholesterol (atherosclerosis). This can lead to heart attack and some studies have indeed shown an increased risk of developing coronary artery disease but only in very heavy coffee drinkers.
Second, coffee has been known to induce cardiac arrhythmias or heart irregularity by stimulating the electrical system of the heart. Coffee may increase the heart rate and thereby raise the blood pressure, which is also deleterious to the cardiovascular system. Coffee has also been known to increase one's cholesterol level as well as levels of homocysteine, harmful amino acids that can aggravate atherosclerosis in the coronary arteries.
Numerous scientific studies haven been done to try to study the effect of coffee on all of the aforementioned cardiovascular problems, and there have been conflicting results. So what do we believe? A good scientific study is one that studies a large number of subjects over a long period of time and in which accurate measurements of the effects in the body can be made. The effects must also be consistently reproducible by different researches.
For a week pharmacological agent like coffee, it has been quite difficult to draw firm conclusions in many of the studies. For example a Norwegian study of 38,500 subjects over 12 years found that coffee consumption was associated with increased risk of death from coronary artery disease, but only when nine or more strong cups of Scandinavian coffee were drunk.
In the Nurses’ Health Study in the US in which 85,747 subjects were studied over a period of 10 years, researchers were unable to find any link between coffee drinking and risk of coronary heart disease. In the Scottish Heart Health Study involving 10,359 subjects over a period of almost eight years, it was found that non-coffee drinkers had a significantly higher risk of coronary heart disease than the coffee drinkers, thus suggesting that coffee was good for the heart.