MEDICAL MATTERS: According to legend, the first cup of tea was made by accident. In 2737 BC a servant of the Chinese Emperor Shen Nung boiled up a pot of water when some leaves from a nearby tea tree fluttered into the boiling water and the attractions of the mixture were quickly recognised.
Centuries later William Gladstone extolled the virtues of tea when he said: "If you are depressed it will cheer you; if you are excited, it will calm you".
I have to admit to being fond of more than the odd cup. Not the usual, thickly made, heavily milked variety of the building site, but rather a well-diluted brew of Earl Grey, lightly milked.
Patients are used to seeing a mug beside my prescription pad and stethoscope; as I write this column a cup of "camellia sinensis" is cooling nicely beside me. I suspect the only reason I do not drink even more is that I like to sip it slowly, unbothered by the gradual cooling.
Which may be just as well, having read a case report in the Lancet titled: "Earl Grey Tea Intoxication". An Austrian doctor describes the case of a 44-year-old man who suffered muscle cramps.
He had been drinking four litres of black tea every day over the past 25 years. However, one week after changing to Earl Grey, he noticed repeated muscle cramps in his right foot. After five weeks the cramps had spread to his left foot, both hands and his left calf. The patient also developed pins and needles in all four limbs and occasionally he noticed involuntary movements in the muscles of his thumb and calf.
He was extensively tested for all manner of diseases by his doctor; all tests were normal.
Convinced that it was the change of tea, he decided to stop drinking Earl Grey and reverted to pure black tea again. One week later, his symptoms had completely disappeared.
The solution to this case lies in the composition of Earl Grey tea. As well as black tea leaves, it contains essence of bergamot oil, which has a pleasant, refreshing scent. Bergamot contains the psoralen derivatives bergapten and bergamottin. The adverse effects of bergamot oil in this patient are explained by the action of bergapten as a potassium channel blocker within muscle cells.
By interrupting the normal flow of potassium, the cells become hyperexcitable, leading to the visible movements and cramps within the muscles.
By drinking four litres a day of Earl Grey (equivalent to at least 16 cups of tea), the Austrian man was simply overdosing on essence of bergamot.
Meanwhile in the Netherlands, a more serious intoxication with herbal tea has been reported. Some 63 people became ill with vomiting, hallucinations and epileptic seizures after they drank herbal tea containing Japanese Star Anise instead of the Chinese Star Anise herb. The Japanese version contains anisatin which blocks a key neurotransmitter in the brain. There were no fatalities but 22 people required hospital admission.
More than 3 billion kilogrammes of tea made from the leaves of the plant "camellia sinensis" is consumed worldwide every year. By adding spices and flavourings, more than 2,000 varieties are produced, so it is not surprising that some of these additives can cause health problems.
On a more positive note, tea is associated with health benefits. Initially, these were linked with the lesser common, green tea varieties, but research has confirmed that black tea is good for you also. Black tea is made from tea leaves that have been withered and dried; green tea is made from fresh leaves. Drinking up to four cups of black tea a day improves the function of the blood vessels in people with coronary artery disease. The endothelium, or lining of cells inside every blood vessel, controls blood flow and the formation of clots. Tea drinkers with heart disease exhibited improved endothelial function compared with a group of patients who drank water.
Green tea has been shown to be a potent anti-cancer agent. Swedish scientists have found that two to three cups of green tea a day reduced the production of new blood vessels by up to 70 per cent.
Since tumours need to generate blood vessels to feed their growth, this effect literally starves cancers to death.
Both green and black tea contain antioxidants, compounds that help the body fight harmful molecules called free radicals. These have been implicated in the development of coronary heart disease and cancers. Antioxidants - such as flavanoids found in tea - mop up the free radicals in the body and help prevent chronic disease.
Tea is a rich source of potassium, magnesium and vitamins A, B1, B2 and B6. Magnesium helps bone growth and potassium is important for nerve and muscle function. And, of course, tea contains less caffeine per cup than coffee does.
So while the Austrian case history has dented my belief in the harmless pleasures of Earl Grey, I am still happy to quote Alexander Woolcott who praised tea as a substance that is not "immoral, illegal or fattening".
Dr Muiris Houston can be contacted at mhouston@irish-times.ie but regrets he cannot answer individual medical queries.