Caffeine is one of a number of biochemically active compounds found in tea and coffee. Smaller but substantial quantities may also be found in chocolate, cola-based drinks and number of medicinal preparations, particularly painkillers. Caffeine has a number of important actions, both on cardiovascular and the central nervous systems.
Consumption of tea and coffee in the UK, Europe and USA has been increasing considerably over the last few years. An average cup of strong tea contains 50mg, and that of coffee 100mg, of caffeine, but variations are considerable. Pharmacological effects can be experienced from 50mg upwards, and doses exceeding 250mg are likely to produce significant effects. The decaffeination of coffee removes practically all of the caffeine, but some biologically active agents remain. Because of the biologically activities of caffeine and related compounds, excess tea and coffee consumption may have a number of adverse effects. Obviously, tea and coffee may also be useful as a minor stimulant, and this has been known for quite some time.
- Psychiatric symptoms: anxiety and nervousness, depression, insomnia and aggravation of pre-existing psychiatric states.
- Physical symptoms: passing of excessive amounts or urine, diarrhoea, wind and tummy rumbles, dyspepsia, shakiness and tremor, migraine and withdrawal headache, abnormal heart rhythms, rapid heartbeat, high blood pressure, restless legs at night and high blood cholesterol (approximately 11% increase). Painful or lumpy breasts may improve on stopping consumption of tea, coffee and chocolate, as well as stopping smoking.
Consumption of tea or coffee at mealtimes can reduce the amount of iron absorbed from vegetables to one third. This is particularly important for women of childbearing age who are vegetarian or semi-vegetarian, and who consume anything other than minimal quantities of tea and coffee, as they may run the risk of becoming iron deficient. Tea and coffee also inhibit zinc absorption.
An interesting syndrome of restless or jumpy legs was described as long ago as the seventeenth century. The sufferer complains of an uncomfortable kicking sensation, felt mainly in the lower legs. It only appears at rest, and usually is troublesome at night, and may complicate caffeine-induced insomnia. It often responds to the withdrawal of tea and coffee. Caffeine is also a potent stimulator of gastric acid secretion, but decaffeinated coffee is even more active in this respect.
Some actual or potential beneficial effect of tea and coffee
- Asthma – The stimulant effects of caffeine can have a beneficial effect in asthma. Caffeine is chemically similar to theophylline, a potent medicine used in treating asthma.
- Pain Relief – Caffeine appears to be effective in improving the efficacy of minor painkillers.
- Nutritional Value – Tea in particular can be a good source of certain minerals, especially manganese and fluoride.