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Ten things you never knew about… caffeine

1) In 1859, the eminent physician Henry Hyde Salter wrote: ‘One of the commonest and best reputed remedies of asthma.. And one that in many cases is more efficacious than any other, is strong coffee.’

2) In 1991, one of the mainstays of asthma treatment is theophylline, a drug closely related to caffeine and only marginally more potent.

3) A cup of instant coffee contains 60-100mg of caffeine, whilst percolated coffee may contain up to 175mg per 150 ml cup. Caffeine levels in tea depend on brewing time, but are typically 40-60mg per cup. Hot chocolate averages 5mg per cup, cola drinks have around 40mg per can, and even a small chocolate bar contains about 20mg of caffeine.

4) The American Psychiatric Association’s manual of recognised conditions, DSM-III-R, includes a specific diagnosis of ‘caffeinism’, classified as an organic mental disorder.

5) Habitual users who stop their caffeine intake develop a withdrawal syndrome within 24 hours, which may last up to a week. Headache and fatigue are the commonest symptoms, but anxiety, nausea, vomiting and craving may occur.

6) A number of studies have shown a strong link between consumption of caffeine-containing drinks and the premenstrual syndrome. There is also some evidence that caffeine reduces fertility.

7) Despite recent anxieties over coffee and pancreatic, bladder and breast cancer, at present there is no strong evidence that caffeine contributes to cancer.

8) Caffeine has been tried as a treatment in a variety of medical disorders, without much success — except in newvorns with poor respiration, where small doses of caffeine improve and regularise breathing.

9) Heavy caffeine users are much groggier in the morning than others — and in some, caffeine produces excessive daytime sleepiness.

10) Many ‘over-the-counter’ painkillers and cold cures include caffeine — in doses up to 95mg — as one of the ingredients, despite the lack of evidence for benefit. In any case, a similar dose could be provided by a cup of instant coffee at a much lower cost.