The amount of caffeine in one or two cups of average-strength coffee can produce mild effects including:
- Increased alertness and energy.
- Alterations to mood.
- Increased metabolism.
- Elevated blood pressure.
- Increased body temperature.
- Increased urination.
- Increased gastric acid secretion.
Caffeine can help people to stay awake. If taken before bedtime it can delay the onset of sleep, shorten sleep time, decrease the depth of sleep and decrease the amount of dream sleep.
Caffeine has been reported to improve the performance of some athletes at a professional level. However, most people will not benefit from consuming caffeine before participating in sport. The consumption of caffeine before or during exercise may cause dehydration. This is because caffeine is a diuretic (meaning it increases the production of urine).
The effects of caffeine in large doses (ie. more than 600mg or eight average cups of coffee) include headache, hand tremors, impaired coordination, nervousness, diarrhoea and even delirium.
Very large doses (10g or more) can produce high blood sugar and urinary acid levels. Ten grams is equivalent to 100 - 200 cups of coffee or tea.
Most adults can consume up to 300mg of caffeine (four average cups of coffee per day) without experiencing unpleasant side-effects. However, some people are sensitive to caffeine and may experience tremors, nausea and insomnia, even when small amounts are consumed.