Feature

Caffeine Anxieties

Should we be worried about drinking tea and coffee and cola?

Dr Rob Hughes

One of the most heavily consumed drugs we know is found in varying amounts in coffee, tea, some soft drinks, chocolate and also in a number of pharmaceutical products -- caffeine. Several years ago, dire health risks such as heart attacks, cancer of the kidneys and bladder, and breast cysts were associated with habitual use of caffeine. However, it is now realised that much of this earlier research failed to take sufficient account of the effects of smoking, alcohol use, obesity and age. Consequently, the physical health risks of caffeine for normal, healthy people now seem minimal and in no way approximate the risks of alcohol and tobacco use. But this does not mean that caffeine is entirely devoid of any unpleasant short-term consequences.

Withdrawal Symptoms

One quite common consequence is the withdrawal headache that can follow the sudden interruption of regular consumption. It usually starts as a feeling of lethargy on the first morning of withdrawal. Then there is the appearance of a localised headache which gradually becomes more generalised and throbbing by afternoon and reaches its peak in about 8-9 hours. The headache may also be accompanied by nausea, vomiting, drowsiness, frequent yawning and even mental depression.

The most effective form of treatment is caffeine itself (such as caffeinated drink or a caffeine-containing headache remedy). Withdrawal headaches often occur during weekends when less caffeine may be consumed than during the working week. The headaches arise from excessive dilation of blood vessels on the surface of the brain when caffeine is withheld. Caffeine usually constricts these blood vessels -- hence its inclusion in some headache remedies.

Another of caffeine's unpleasant relatively short-term effects is its ability to induce symptoms of anxiety when consumed in excessive amounts. Even though scientists and clinicians have only undertaken serious investigations of the anxiety-inducing effects of caffeine during the last 30 years, its ability to produce "nervousness" when consumed in coffee and tea has been recognised for much longer.

In the eighteenth century, American physicians referred to a number of undesirable consequences of drinking strong tea, amongst which "nervousness" featured prominently. A notable example was one of the signatories of the American Declaration of Independence, Benjamin Rush, who described tea when drunk too strong as "a slow poison" that caused irritability. He believed that it led to nervousness and weakness.

Today it is known that regular consumption of high levels of caffeine can lead to a condition known as "caffeinism" which is virtually indistinguishable from a severe anxiety disorder. Caffeinism involves strong feelings of anxiety plus other symptoms such as sleep disturbances, periods of depression, diarrhoea, headache and heart palpitations. These symptoms do not usually respond to tranquilising drugs (such as Valium or Ativan) since the presence of caffeine in the blood stream interferes with their action. The only reliable form of treatment for caffeinism is to drastically reduce caffeine intake (with the possible risk of a withdrawal headache developing).

Although there are wide individual differences in tolerance for the drug, to entirely avoid even the slightest risk of caffeinism, daily consumption of no more than about 500 mg of caffeine (6-8 small cups of coffee) is advisable. This level could be even lower in women who are pregnant or taking oral contraceptives, the elderly, or people with liver disease, since all of these conditions slow down the clearance rate of caffeine from the body. For most coffee and tea drinkers, the real risk of caffeinism does not appear until daily consumption approaches 1,000 mg.

Even with daily levels of caffeine that are lower than those likely to produce full-blown caffeinism, there is the possibility of milder anxiety states developing. But a problem with much of the research is the difficulty in determining if the anxiety was the result or the cause of excessive caffeine. In her 1983 thesis research at the University of Canterbury, Mary Shanahan found that undergraduate students increased their tea and coffee drinking during periods of stress in the belief this would have a calming effect.

However, reasons for regularly drinking caffeinated beverages may be entirely unrelated to any real or imagined soothing effects ascribed to them. For example, many psychiatric inpatients drink large quantities of coffee and tea in an attempt to slake thirst or counteract sedation produced by some forms of medication, or to merely relieve boredom.

For people who do not regularly consume caffeine, a single experience with the drug may or may not produce anxiety. However, a single experience definitely seems capable of exaggerating the anxiety-producing effects of some other stressful event. For example, while by itself having no effect, when paired with exposure to a stressful situation (such as an insoluble high level reasoning task), caffeine can further increase the feeling of anxiety and its accompanying physical symptoms.

The combined effects of various stressors and caffeine in both humans and animals demonstrate that stress can increase sensitivity to any anxiety-producing potential of the drug. This has particular relevance to the control of anxiety disorders since there is now ample evidence that caffeine can exacerbate certain conditions, especially panic disorder (PD). As implied by its name, PD is characterised by panic attacks involving extreme terror which may last from a few minutes to several hours. These panic episodes are interspersed with intervening states of anxious anticipation of future episodes. Ingestion of caffeine can trigger a panic reaction, a fact well-recognised by sufferers who tend to voluntarily restrict or even entirely avoid the drug.

So, caffeine can produce caffeinism-related anxiety in formerly non-anxious people and also worsen an existing anxiety disorder. More importantly for most people, caffeine is capable of exacerbating the anxiety-producing effects of stressful situations. This clearly could have undesirable consequences for those inclined to increase their caffeine intake during times of stress. The practice popular with many students of taking caffeine tablets (No Doz), often in combination with coffee or tea, to stave off sleep while studying for examinations could be disastrous for anyone prone to problematic examination anxiety.

In generalising to the population at large from the results of scientific and clinical studies of caffeine's anxiety-inducing potential, it is important to remember that there are wide individual differences in responsiveness to the drug. One intriguing source of these differences is whether or not an individual smokes, since the presence of nicotine in the bloodstream increases the rate of clearance of caffeine from the body. Ironically then, smokers may be less susceptible to the anxiety-producing and any other effects of caffeine than nonsmokers.

Dr Rob Hughes is a Reader in Psychology at the University of Canterbury.