Do you need your morning coffee to get moving? Coffee, which provides the stimulant caffeine, is the most popular drink in the world. Apparently we’re more and more taken with caffeine in its popular form: over the last 10 years, the number of coffees served in Australia has risen by 65% (Reference: BIS Shrapnel "Coffee in Australia" 2006-2008).
Caffeine also occurs naturally in other beverages including tea, soft drinks, chocolate and cocoa. Caffeine stimulates the central nervous system, causing an increase in heart rate and blood pressure, resulting in a feeling of alertness and energy. Caffeine is also a diuretic, meaning it stimulates the kidneys to create more urine.
The debate about caffeine and coffee is centuries old. Roman clergymen wanted Pope Clement VIII to ban coffee because it was the “Devil’s Drink,” as revenge for the Muslims banning wine as demonic. The Pope refused, however, and even blessed it, making it a “Christian beverage.” In popular culture at the time, however, coffee houses were thought to be dens of immorality. These days, we might not condemn caffeine consumers as demonic, but there is significant ongoing debate about whether caffeine is beneficial or harmful to our health and fitness.
The physiological effects of caffeine are well documented. The National Library of Medicine in Washington DC counts more than 19,000 scientific studies to date on coffee or caffeine. Caffeine’s effects range from the behavioural to the physiological, and can very considerably from one person to the next. However, caffeine does speed metabolism and is included in many weight-loss products. It also increases the breakdown of fat during exercise, which is appealing to many recreational athletes. At the same time, blood glucose is conserved, warding off hunger and stimulating intellectual activity: the brain functions exclusively on glucose. For these reasons, students often develop something of a dependency on coffee, to combat long nights and little sleep and to meet their needs for study.
Moderate consumption of caffeine, which is equivalent to about 2-4 cups of coffee per day, is generally seen as safe and many see it as beneficial. There is evidence that moderate caffeine consumption may lower the risk of colon cancer, gallstones, cirrhosis of the liver, and Parkinson’s disease. It also may reduce asthma symptoms (see our related research article on exercise-induced asthma). Coffee contains four times the antioxidants in green tea, and it generally provides greater alertness and energy for both mental and physical exertion.
For athletes and those who wish to lose weight, caffeine improves performance and increases calorie expenditure. A Danish study showed that one cup of coffee increased the metabolic rate by 3-5%, while making more fat available to muscles during exercise. The result is greater energy and endurance. The American College of Sports Medicine (ACSM) has conducted research on well-trained, recreational athletes in the laboratory. The results showed that consumption of 3-9 mg of caffeine per kilogram (kg) of body weight one hour before exercise increased endurance running and cycling performance. The “glucose sparing” effect of caffeine is cited as the reason for the improved performance. The effect is well-enough documented that the International Olympic Committee has limited urinary caffeine content to 12 mg/mL (4 to 7 cups of coffee over a 30-minute period would result in disqualification of an athlete).
In terms of the downsides of caffeine, consuming too much causes side effects like anxiety, jitters, insomnia, gastrointestinal discomforts and light-headedness. Athletes should note that caffeine is a diuretic, meaning they should consume more water to counteract the dehydrating effects. There is evidence that caffeine is dangerous for pregnant women, because it can lead to miscarriage or low birth weight. Also, women who are iron-deficient should be aware that caffeine can interfere with iron absorption, especially if you consume it with meals. Caffeine also interferes with calcium absorption, which can contribute to osteoporosis. Adequate consumption of calcium (one glass of milk for every 2 cups of coffee) can offset this problem.
Many people find caffeine disturbs their sleep. Even if caffeine doesn’t keep you awake, it stays in your system long enough that your sleep may not be as deep or of as good quality as if you didn’t consume caffeine. The best advice in this regard is to drink coffee early in the day and avoid it altogether within 6 hours of going to bed.
As with many substances, the key to caffeine lies in moderate and sensible use, and avoidance if it is contraindicated (as with pregnant women). A cup or two of coffee a day is generally seen as safe and enjoyable, and may provide you with mental and physical benefits that enhance your quality of life.