Caffeine intoxication usually occurs with consumption above 250mg (equivalent to about 2 1/2 cups of coffee). Caffeine is a central nervous system stimulant and may be taken to help restore mental alertness when unusual tiredness, weakness or drowsiness occurs. Caffeine's use as an alertness aid should be only occasional. It is not intended to replace sleep and should not be used regularly for this purpose. The amount of caffeine in some common foods and beverages is as follows:
|Coffee, brewed||40 to 180mg per cup|
|Coffee, instant||30 to 120mg per cup|
|Coffee, decaffeinated||3 to 5mg per cup|
|Tea, brewed American||20 to 90mg per cup|
|Tea, brewed imported||25 to 110mg per cup|
|Tea, instant||28mg per cup|
|Tea, canned iced||22 to 36mg per 12 ounces|
|Cola and other soft drinks, caffeine-containing||36 to 90mg per 12 ounces|
|Cola and other soft drinks, decaffeinated||0mg per 12 ounces|
|Cocoa||4mg per cup|
|Chocolate, milk||3 to 6mg per ounce|
|Chocolate, bittersweet||25mg per ounce|
Caffeine also increases blood pressure, even in healthy individuals, but particularly in the elderly. Persons who already suffer from high blood pressure may find that ingesting large quantities of caffeine pushes their blood pressure up to unacceptable levels.
Excessive intakes of caffeine contribute to osteoporosis and may interact negatively with prescription medications.
Research indicates that women who ingest excessive quantities of caffeine, do not conceive as fast as women who drink moderate quantities of this stimulant.
The birth weight of babies born to pregnant women who drink or eat too much caffeine may be low, which exposes the newborn to a number of risks.
In addition, caffeine passes into breast milk and can transfer all the negative effects listed above to the infant. So, if a baby is irritable, restless or exhibits any of the other side-effects of caffeine excess, this may be due to the mother ingesting too much caffeine.
Caffeine intoxication is known to cause rambling thought and speech.
It almost goes without saying that coffee decreases the quality of sleep and is one of the leading causes of sleep disturbance. Coffee drinkers are sleepier and groggier than non-coffee drinkers when they get up in the morning, causing them to depend on coffee to get them going. This grogginess may be the result of their entering caffeine withdrawal during the night, or that drinking coffee kept them from sleeping well in the first place, or both.
Excess caffeine levels cause restlessness. Caffeine has been shown to increase subjects' proneness to develop RLS at lower levels of blood glucose. It is therefore no surprise that a xanthine-free diet (no coffee, tea, cola beverages, cocoa) has been reported to be another effective dietary measure RLS sometimes following a short period of caffeine withdrawal. [J Clin Psychiatry 39: pp.693-8, 1978; Ann Intern Med 119: pp.799-804, 1993]