• persistent anxiety
• an inability to concentrate
• increased muscle tension
• diuresis (increased urination)
• agitation, excitement and panic attacks (with high doses)
• vertigo, dizziness, tinnitus, convulsions
• increased body temperature
• confusion, disorientation, paranoia
• palpitations
• nausea
watch out!
A good night’s sleep does not result from high doses of alcohol. A night’s sleep deprivation will enhance the effects of alcohol and after five nights of partial sleep loss, three drinks will have the same effect on your body as six would on a regular night.
must know
Caffeine
• Caffeine is readily absorbed and peak concentrations occur 30-60 minutes in young adults after ingesting it. High doses slow the metabolism down and can remain in the brain for 9-15 hours.
• Percolated coffee usually contains more caffeine than instant. If the coffee grounds are boiled during preparation, as is common in Scandinavian countries, the caffeine content can be as high as 500mg per cup.
• Tea brewed directly from crushed leaves has more caffeine than tea produced with a tea bag.
• Plain chocolate contains more caffeine than milk chocolate.
Caffeine enters the bloodstream very quickly and can take between three and seven hours to leave the body. Its effects on people can be variable – some people regularly drink caffeine-laden drinks at night-time with no ill-effects; others cannot even drink one cup in the morning without it affecting them at night. Scientists believe this may be because caffeine-sensitive individuals metabolize the substance more slowly (see opposite, for factors involved in metabolizing caffeine).
Research shows that if you are not a habitual coffee drinker, the effects will be greater; and that caffeine metabolism varies with age (children, for example, tend to metabolize it more quickly).
Although caffeine is normally associated with coffee, it is found in medicines and many other foods and drinks, namely:
• tea
• chocolate, cocoa and all other chocolate-flavoured products
• over-the-counter stimulants (e.g. Pro-plus)
• painkillers (e.g. Anadin)
• herbal preparations (e.g. Guarin)
• some cola drinks
• Lucozade
• ‘energy’ drinks (e.g. Red Bull)
To find out how much caffeine you are really consuming, see the main caffeine offenders, opposite.
The absorption and metabolism of caffeine
Varied or little effect
Heredity Caffeine metabolism is controlled by many genes and racial differences exist
Gender Exercise and stress have no reliable effect on the absorption or metabolism of caffeine
Pregnancy There are no placental barriers to caffeine so the foetus is continuously exposed
Slowers-down
Oral contraceptives, late pregnancy and liver disease cause caffeine to be eliminated more slowly
It has been thought that grapefruit juice, though not other citrus juices, slows down metabolism. The data for this has now proved controversial
Some drugs like cimetidine, disulfiram, even alcohol, may slow down caffeine metabolism
Speeders-up
Smoking induces liver enzymes which break caffeine down
Rifamprin
The main caffeine offenders
| Foodstuff | Plant | Plant caffeine content w/w | Caffeine dose/‘cup’ |
|---|---|---|---|
| Tea | Dried leaves | 1-5% | 10-100mg (average 40mg) |
| Coffee | Beans | 0.75-2.0% | 30-150mg |
| ‘Decaffeinated’ coffee | Beans | 0.75-2.0% | 5mg |
| Cocoa | Seeds | 0.013-1.7% | 2-50mg (average 5mg) |
| Chocolate | Seeds | 2-63mg/50g | |
| Cola drinks | Nuts | 1.5-2.0% | 25-100mg (synthetic) |
did you know?
Coffee is an ancient commodity. In AD 575, about 500 years before it became a hot beverage, the crushed beans were mixed with fat and used by Ethiopian mountain warriors to provide an energy boost during long treks and warfare.
must know
Sugar
Sugar does not give you energy. A study carried out at Loughborough University, UK evaluated the energy-giving effects of sugar on ten healthy young adults. Their sleep was restricted to five hours the night before so that they would be sleepy in the afternoon, and half were given a ‘high-energy’ drink containing high levels of sugar but low levels of caffeine, and the other half a drink containing low levels of both. When submitted to vigilence and sleepiness tests the high-sugar drinkers made twice as many errors and showed higher levels of sleepiness than the control group, as well as delayed reaction times.
Sugar
Sugar can have a negative impact on sleep patterns because of its effect on insulin and blood sugar levels. It is released into the bloodstream to give you that instant ‘high’, but then departs from your system just as quickly, leaving you exhausted. In fact, you feel so tired that your instant impulse is to have yet another sugar fix to make you feel better. And so the cycle goes on. The continuing effect of these highs and lows can leave you feeling drained, or – depending on when you last had your sugar dose – over-excited, with pounding palpitations that stop you from sleeping. The disruptive impact on blood sugar levels can also cause sleep-disrupting hormonal imbalances in women. Sugar is found