Caffeine is a mild stimulant that can increase wakefulness and elevate mood. Some people also claim that caffeine gives them energy. However, this energy boost is probably derived from the sugar or carbohydrate that is also in the caffeine-containing beverage or food rather than the actual caffeine itself.

The effects of caffeine on health are not well understood, despite many years of research. For most healthy adults, moderate amounts of caffeine – about two to three cups of coffee (200-300mg caffeine) per day – do not pose any physical problems.

How caffeine affects the body

Caffeine is a central nervous system stimulant. It affects the body in different ways and individuals have different thresholds of sensitivity. Therefore, the amount that will cause ‘coffee jitters’ or other effects such as alertness in one person will be different in someone else.

The physiological effects of caffeine are varied and include increased mental alertness and concentration, elevated mood, decreased fatigue, improved reaction time and increased fatty acid mobilisation. This last effect is the reason that athletes favour caffeine, because when fat is being used for energy, the precious carbohydrate store is conserved.

Caffeine is also associated with helping people to sober up after drinking alcohol. However, this is a myth. While moderate intakes do not cause any harm, excessive caffeine can cause anxiety, insomnia, headaches or stomach irritation.

Caffeine was traditionally thought of as a diuretic (increasing urine output). However, more recent research suggests that this is not the case.

Foods high in caffeine

Coffee is a major source of caffeine but tea also has high levels and a strong cup of tea can contain up to twice as much caffeine as a cup of instant coffee. Soft drinks also contain caffeine. However, although most people know that cola drinks contain caffeine, you might be surprised to know that it is also found in orange drinks. Another surprising fact is that a mug of hot chocolate contains as much caffeine as a can of cola.

Many energy drinks contain large amounts of caffeine and are advertised as helping sporting performance. However, the Food Safety Authority of Ireland recently reported that these drinks are not suitable for use before, during or after sport. Caffeine is included on the list of ‘banned substances’ by the International Olympic Committee (IOC). The IOC limit for caffeine concentration in the urine is 12µg/100ml.

Serious athletes have to limit their intake of caffeine-containing foods significantly, as 350mg of caffeine can produce this effect in urine. The table below lists the caffeine content of everyday foods and drinks.

Food                                                             Caffeine (mg)

Strong tea (200ml)                                     80 - 120
Instant coffee (200ml)                               65 -  100
Percolator coffee (200ml)                         115 - 1754
Espresso (1 serving, 50ml)                     100
Cola drinks (330ml can)                           30 - 65
Chocolate bar (200g)                                 50
Red Bull                                                        80

How to cut back on caffeine

If you suspect that your caffeine intake is high, it is a good idea to keep a diary and record your consumption of all the caffeine-containing foods and drinks that are listed above. Record the time of day as well as the food or drink you consume. Regular caffeine consumption can lead to reduced sensitivity and so caffeine intake can creep up.

For example, do you know anyone who drinks two cups of coffee in the morning to get going rather than one cup?

Do you go for a large cappuccino (with a double shot of espresso) more often now than before?

If you think your caffeine intake is increasing or if you experience symptoms such as insomnia, anxiety, headaches or stomach irritation, it is a good idea to slowly cut down your intake. Use your caffeine diary to help isolate things you could change, e.g. drinking herbal tea instead of coffee at 11am, choosing an energy bar rather than chocolate, or drinking water instead of caffeine-containing beverages.

A gradual reduction in caffeine intake is advised to help avoid withdrawal symptoms. When caffeine intake is reduced too quickly, many people experience symptoms such as headache, irritability and restlessness.

Who should avoid caffeine?

There are many reasons why we should limit the caffeine intake in our diet, including medical conditions such as high blood pressure, kidney problems, gastritis, ulcers or osteoporosis. People suffering from these conditions need to carefully monitor their intake of caffeine. Pregnant women and women who are breastfeeding should also restrict their caffeine intake.