According to the annual National Drinks Survey, adults in the UK drink an average of 3.1 cups of tea and 1.44 cups of coffee every day. If this is true, there must be a lot of people not drinking their quota, because everybody I know drinks three times as much. One headteacher went to the doctor complaining of palpitations and was asked to keep a record of her daily intake. The shocking total was 14 cups. Sure enough, when she substituted a few Blueberry Bracers, her symptoms disappeared.

Health-promoting diets invariably tell us we should cut down on tea and coffee. The reason they are bad for us, of course, is precisely what attracts us to them. Caffeine, the stimulant drug in coffee, tea, cocoa, chocolate and many soft drinks, is the most widely used psychoactive substance in the world. In its pure form, a spoonful would be enough to kill you, but you would have to drink buckets of coffee to ingest a fatal dose. A cup of strong tea contains around 80mg of caffeine and a mug of strong coffee up to 200mg.

Because individual reactions are governed by genes, age, and the tolerance built up through habitual use, however, it’s hard to say how much is too much. One way to measure your dependence is to abstain for a day and find out if you suffer withdrawal symptoms (headache, a hangover or cravings).

Caffeine has a galvanising effect on all the organs and tissues of the body. In small amounts, it acts on the brain to improve concentration, reduce fatiue and speed up reactions; it also stimulates the muscles and aids digestion. Excessive use magnifies these effects unpleasantly, leading to restlessness, anxiety, irritability, twitchiness, palpitations and insomnia. Caffeine also masks the symptoms of tiredness which are the natural warning signs that your body and mind need a rest, allowing you to wear yourself out with work (or partying). And on top of all this, recent research has suggested that tea can block the body’s ability to absorb certain nutrients, so drinking tea with a meal is especially bad for you.

The commonly prescribed alternatives are herbal infusions. I am currently working my way happily through the staggering 118 different varieties stocked by my local healthfood shop. They range from traditionally medicinal (peppermint for digestion, valerian for insomnia), through fashionable (echinacea for disease resistance, gingko for memory) to implausible (Slimatee, Forever Young).

But these infusions, which often look like old dishwater and sometimes taste like it, are not everyone’s cup of tea. Besides, there’s more to the traditional cuppa than the caffeine. For many of us, tea-drinking is more important for its connotations of comfort and congeniality than for its pharmaceutical effects. In the 400 years that tea and coffee have been drunk in Britain, there has been no evidence that moderate indulgence does serious harm. So cut down from 14 a day, certainly; throw away the sugar and use semi-skimmed milk. But what would teaching be without the tea at the beginning?