Coffee (caffeine) and its effects in the human body

Sources of caffeine

Caffeine is an alkaloid compound, in pure form odorless and bitter in taste. Caffeine is one of many alkaloids (including theophylline and theobromine) which occur naturally and in varying amounts in leaves, seeds, and fruits of more than 60 plants. These plants include coffee (from which the beans are used), tea (leaves), cacao (pods), cola or kola (nuts), Yerba matè (leaves), guarana (berries), and Yaupon holly (leaves). Caffeine is consumed from these sources in beverages and foods such as tea, coffee, chocolate, cocoa, matè, caffeinated soft drinks, caffeinated pills, coffee beans, and some drugs (eg analgesics such as aspirin). Significantly, coffee comes second only to petroleum as the world's most widely traded commodity.

Effects of caffeine

What caffeine does to the body

There is no physiological requirement for caffeine in the human diet. Caffeine is a stimulant of the central nervous system (CNS), the cardiac muscle (increases heart rate), and respiratory system (relaxes air passages permitting improved breathing, and allows some muscles to contract more easily). It acts as a diuretic (increases the rate of bodily urine excretion), and delays fatigue (having the effect of warding off drowsiness and restoring alertness). For these reasons, caffeine is probably the most popular drug in use. The effects you might notice after consuming a large cup of coffee are hands getting cold, muscles tensing up, feeling of excitement and increased heart beat.

The related alkaloids theophylline (found mainly in tea) and theobromine (in cocoa beans, cola nuts and tea) act as a cardiac stimulant, smooth muscle relaxant, diuretic, and vasodilator (widening or dilating blood vessels in the body).

Persistence of caffeine in the body

Caffeine absorption occurs in the body very quickly - caffeine enters the bloodstream through the stomach and small intestine, and its effects are felt as soon as 15 minutes after consumption. It is completely absorbed within 45 minutes of ingestion. Caffeine does not accumulate in the bloodstream nor is it stored in the body, but it does persist - only about ½ is eliminated in the urine within 6 hours.

Caffeine and metabolism - caffeine does not suppress the appetite, although it does increase the level of circulating fatty acids, thereby enhancing fat oxidation. This is why caffeine is used by runners and endurance trainers, although it is most effective in non-habitual users. Also, contrary to popular belief, the effects of alcohol are not reduced by caffeine, although as mentioned above it can provide temporary relief from fatigue and drowsiness, and from migraine headaches.

Caffeine sensitivity refers to the amount of caffeine that will produce negative side effects in a particular person. Regular caffeine consumption reduces sensitivity to caffeine, and a higher intake is needed for the same effects. So caffeine is considered to be an addictive drug.

Caffeine withdrawal symptoms - when caffeine intake is reduced, the body then becomes oversensitive to a chemical in the brain (adenosine) relevant to the sleep process, causing blood pressure to drop dramatically, producing an excess of blood in the head area (not necessarily on the brain), and leading to a headache often lasting several days. Other withdrawal symptoms reported are fatigue and muscle pain, irritability, inability to work, nervousness, restlessness, and feeling sleepy, and in extreme cases, nausea and vomiting. Gradual reduction of caffeine intake abates these symptoms.

Level of caffeine intake

Moderate caffeine intake has no apparent health risk - 3 8oz/230ml cups of coffee per day (total about 250 milligrams of caffeine) is considered moderate, while 10 cups is considered excessive. One study suggests minimum consumption of caffeine to produce physical dependence is 4 cups of coffee per day, while other studies suggest a few more than 3 cups.

More than moderate consumption of caffeine can increase alertness, but also reduce fine motor coordination and cause insomnia, headaches, dizziness and nervousness.

Massive doses of caffeine (above 10g, about 170mg/kg of body weight), can be lethal, although this equates to drinking more than 80 cups of coffee in rapid succession!

Caffeine reduction in coffee beverages can be achieved by using chicory as a blend with the coffee (or even as a substitute). The root of the chicory plant is dried, roasted and ground, producing a caffeine-free product acceptable for a coffee-like beverage. Many coffee producers offer a coffee/chicory blend of up to 30% chicory.

Coffee preparation

The coffee beverage may be produced by one of a number of methods:

• Filter - Hot water is passed through finely-ground coffee within a filter
• Plunger/Cafetiere - Hot water is added to coarsely-ground coffee, and after steeping for 3-5 minutes a plunger with a fine mesh base is used to separate the grounds from the infusion
• Percolator - Coarsely-ground coffee in water is boiled and bubbled to the top of the percolator
• Espresso - A machine forces hot water through very finely-ground, compacted coffee into cups below. When properly prepared by a 'barista', the result is a golden brown liquid called the 'crema' on top of black coffee. One espresso 'shot' is between 1.5 fl oz/44 ml and 1.75 fl oz/52 ml, produced from 7 grams of ground coffee.
• Moka-Nepoletana - In a combination of espresso and percolator methods, water is boiled in the lower container of a double-chambered pot, and forced up through a tube then down through finely-ground coffee.
• Arab or Turkish - Finely-ground coffee with sugar in a cupful of water, is brought to the boil then taken off the heat up to 3 times, before being poured to drink as a strong-tasting coffee.

Specialty and convenience coffee drinks include:

• Cappuccino: Espresso, some milk, and a thick head of milk foam, often sprinkled with cinnamon or cocoa powder
• Latte: Espresso with lots of milk
• Mocha: Latte with chocolate, often topped with whipped cream
• Americano: Espresso shot, plus hot water to fill the cup
• Macchiato: Espresso shot, plus a little frothed milk
• Cafe au lait: Brewed coffee, preferably dark French roast with chicory, with half scalded milk (not steamed), poured into the cuo together.
• Instant (or soluble) coffee: Dehydrated coffee powder or granules to which hot water (and/or hot or cold milk) is added
• Flavoured coffee drinks: Flavours introduced either to the beans after roasting, or after brewing by adding syrups (vanilla, caramel, peppermint etc) or alcohol (eg whiskey for Irish coffee)
• Coffee-infused liqueurs: Irish cream, rum cream etc
• Iced coffee: Brewed coffee, cooled then chilled, and stirred with crushed ice (possibly sweetened and with cold milk added)

Calories in coffee drinks

Unadulterated coffee (that is, only water added) has no calories. The calories in coffee drinks are present in the additives - lattes, mochas, iced espresso blended with sugar, whipped cream, ice cream, flavored syrups, alcohol, and so on.

Conclusion on caffeine consumption

Restrict intake to no more than 250mg of caffeine per day:

• Aim for moderate use of coffee - one serving of coffee ranges from about 40 mg for a single shot (30ml) of arabica variety espresso, through instant coffee 60-80mg, to about 100 mg for strong drip coffee. Caffeine content of coffee beans is between about 1 to 1.4% (Arabica coffee normally contains less caffeine than the Robusta variety). Generally, dark roast coffee has less caffeine than lighter roasts (the roasting process reduces the bean's caffeine content).
• Use decaffeinated coffee, if it has been naturally decaffeinated or Swiss water processed (no chemicals have been introduced). Decaffeinated beans have only about 0.02% caffeine, so that one cup of decaf coffee has only around 2-4 mg of caffeine.
• Be aware of the caffeine content of other beverages (cola's for example), snacks and candy (like chocolate).