When the morning interval bell rings, several thousand teachers across the UK rush for the staffroom and a much-longed for mug of coffee or tea. But are these pick-me-up beverages doing more harm than good?

American researchers have found that regular caffeine users - one cup every day is enough - can have a physical addiction to caffeine. When they kick the habit they get withdrawal symptoms, including headaches, irritability, lethargy, depression, flu-like symptoms and poor concentration. The symptoms can be so severe, they argue, they should be identified as official mental disorders.

Margaret Beveridge, a learning support teacher at Craigroyston Community High School in Edinburgh, found it tougher than anticipated to give up her regular cuppa. “It was part of a general detox,” she says. “I pledged to drink nothing except water, but a headache soon set in. It seemed to go on for days. To say it was distracting when I was teaching is putting it mildly.”

At home, Margaret drank about four cups of tea a day, topped up by a mug of freshly brewed filter coffee at school during the morning break. After a week of detox misery she succumbed to its delicious aroma and was back on the caffeine.

However, about four cups of coffee can be safely drunk each day, advises Dr Sarah Jarvis from the Royal College of General Practitioners. Nervousness tends to affect caffeine novices, she adds, “but there is no evidence that moderate caffeine intake has physical or social consequences remotely comparable to those associated with serious drugs.”

Shen Nung, the Chinese emperor, has been attributed with the discovery of tea through fermenting the leaves of the plant Camellia sinensisi as long ago as 2700BC. Maritime trade started to bring tea to Europe from China and India, as well as coffee from Africa and Latin America, in the late 16th century. Initially the beverages were marketed by enterprising traders as medicinal - possibly because they themselves had discovered their uplifting qualities.

But caffeine’s attributes need managing. “We know caffeine increases alertness, which is useful if we want to boost flagging energies, but not if we want to get to sleep,” says Sarah. “It is not a good idea to drink tea or coffee less than six hours before bedtime.”

Caffeine belongs to a group of chemical compounds known as xanthines and is processed by the enzymes in the liver before being excreted. It acts as a mild diuretic, meaning that it can dehydrate, but it can also count towards our daily water intake. Teachers who stop drinking it must take more water on board to prevent dehydration and further headaches.

Storm in a coffee cup

- The average cup of coffee contains 70 to 100 mgs of caffeine, sometimes twice as much as tea. Filter coffee contains up to 50 per cent more caffeine than instant.

- Caffeine is also contained in some soft drinks, such as cola, and chocolate.

- Stop taking caffeine gradually.

- Young women - who are most at risk of anaemia, a fatigue-inducing iron deficiency - should not have tea or coffee with meals or within 30 minutes after a meal, the Food Standards Agency says. The drinks contain polyphenols that make it harder to absorb iron.

- Pregnant women should not take more than 300mg of caffeine a day. High caffeine intake can cause low birth weight or miscarriage.

Visit www.food.gov.uk.