(see also above)
Coffee, tea and cola drinks in excess can make people tense and anxious. Small children are not usually given tea and coffee because they are thought to be less tolerant of the central nervous system stimulant effect, but cola drinks irrationally escape this prohibition. It is possible to make an imposing list of diseases which may be caused or made worse by caffeine-containing drinks, but there is no conclusive evidence to warrant any general constraints. High doses of caffeine in animals damage chromosomes and cause fetal abnormalities; but studies in man suggest that normal consumption poses no risk. Epidemiological studies are not conclusive but indicate either no, or only slight, increased risk (x 2-3) of coronary heart disease in heavy (including decaffeinated) coffee consumers (> 4 cups/day) (see Lipids, below).
Tolerance and dependence. The regular, frequent use of caffeine-containing drinks is part of normal social life and mild overdose is common. Slight tolerance to the effects of caffeine (on all systems) occurs. Withdrawal symptoms, attributable to psychological and perhaps mild physical dependence occur in habitual coffee drinkers (5 or more cups/day) 12-16 h after the last cup; they include headache (lasting up to 6 days), irritability, jitteriness; they may occur with transient changes in intake, e.g. high at work, lower at the weekend. Habitual tea and coffee drinkers are seldom willing to recognise that they have a mild drug dependence.
Chronic overdose. Excessive prolonged consumption of caffeine causes anxiety, restlessness, tremors, insomnia; headache, cardiac extrasystoles and confusion; diarrhoea may occur with coffee and constipation with tea. The cause can easily be overlooked if specific enquiry into habits is not made; including children regarding cola drinks. Of coffee drinkers, up to 25% who complain of anxiety may benefit from reduction of caffeine intake. An adult heavy user may be defined as one who takes more than 300 mg caffeine/day, i.e. 4 cups of 150 ml of brewed coffee, each containing 80 ± 20 mg caffeine per cup or 5 cups (60 ± 20) of instant coffee. The equivalent for tea would be 10 cups at approximately 30 mg caffeine per cup; and of cola drinks about 2.01. Plainly, caffeine drinks brewed to personal taste of consumer or vendor must have an extremely variable concentration according to source of coffee or tea, amount used, method and duration of brewing. There is also great individual variation in the effect of coffee both between individuals and sometimes in the same individual at different times of life (see Sleep, above).
Decaffeinated coffee contains about 3 mg per cup; cola drinks contain 8-13 mg caffeine/100 ml; cocoa as a drink, 4 mg per cup; chocolate (solid) 6-20 mg per 30 g.
In young people high caffeine intake has been linked to behaviour disorders and a limit of 125 mg/I has been proposed for cola drinks.
Blood lipids. Drinking 5 cups of boiled coffee/day increases serum total cholesterol by up to 10%; this does not occur with coffee made by simple filtration. Cessation of coffee drinking can reduce serum cholesterol concentration in hypercholest-erolaemic men.
Breast-fed infants may become sleepless and irritable if there is high maternal intake. Fetal cardiac arrhythmias have been reported with exceptionally high maternal caffeine intake, e.g. 1.5 1 cola drinks/day.
Ginseng is the root of 2 plants of the same family (oriental, Panax ginseng; Siberian, Eleutherococcus senticosis) and contains a range of biologically active substances (ginsenosides).
It has been used as a tonic or stimulant for thousands of years. In animal studies ginseng doubles the time that mice placed in water can swim before becoming exhausted; it appears to have antifatigue effects in various other tests in mice (climbing up a rope that is moving downwards) and it increases sexual activity. In man, ginseng has been claimed to benefit performance of athletes and astronauts (fewer fatigue-caused errors), and to reduce absenteeism due to respiratory illness in mining and steel workers and truck drivers. Oriental soldiers at war have used ginseng. Despite accumulating evidence and wide use by the public, the medical profession in Western countries remains sceptical of the value of this tonic. A range of adverse effects is reported, including oedema, hypertension, rashes, diarrhoea, sleeplessness and oestrogen-like effects
Khat. The leaves of the khat shrub (Catha edulis) contain alkaloids (cathinine, cathine, cathidine) which are structurally like amphetamine and produce similar effects. They are chewed fresh (for maximum alkaloid content) so that the habit was confined to geographical areas favourable to the shrub (Arabia, E. Africa) until modern transportation allowed wider distribution. Khat chewers (mostly male) became euphoric, loquacious, excited, hyperactive and even manic. As with some other drug dependencies subjects may give priority to their drug needs above personal, family and other social and economic responsibilities. Cultivation takes up serious amounts of scarce arable land and irrigation water.
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