PHARMACODYNAMICS: There are several
known mechanisms of action to explain the effects of caffeine. The
most prominent is that it reversibly blocks the action of adenosine
on its receptor and consequently prevents the onset of drowsiness
induced by adenosine. Caffeine also stimulates certain portions of
the autonomic nervous system.
EFFECTS OF CAFFEINE IN THE BODY: Caffeine can have both positive and
negative health effects. It can be used to treat bronchopulmonary
dysplasia of prematurity, and to prevent apnea of prematurity:
caffeine citrate was placed on the WHO Model List of Essential
Medicines in 2007. It
may confer a modest protective effect against some diseases,
including Parkinson's disease and certain types of cancer. One
meta-analysis concluded that cardiovascular disease such as coronary
artery disease and stroke is less likely with 3–5 cups of
non-decaffeinated coffee per day but more likely with over 5 cups per
day.
Some people experience insomnia or sleep disruption if they
consume caffeine, especially during the evening hours, but others
show little disturbance.
Evidence
of a risk during pregnancy is equivocal. Some authorities recommend
that pregnant women limit consumption to the equivalent of two cups
of coffee per day or less.
TOLERANCE AND DEPENCE TO CAFFEINE: Caffeine can produce a mild form of drug
dependence associated with withdrawal symptoms such as sleepiness,
headache, and irritability when an individual stops using caffeine
after repeated daily intake. Tolerance to the autonomic effects of
increased blood pressure and heart rate, and increased urine output,
develops with chronic use. Caffeine
is classified by the Food and Drug Administration as "generally
recognized as safe" (GRAS).
TOXICITY DUE TO CAFFEINE: Toxic doses, over 10 grams per day
for an adult, are much higher than typical dose of under 500
milligrams per day. A cup of coffee contains 80–175 mg of caffeine,
depending on what "bean" (seed) is used and how it is
prepared. Thus it requires
roughly 50–100 ordinary cups of coffee to reach a lethal dose.
However pure powdered caffeine, which is available as a dietary
supplement, can be lethal in tablespoon-sized amounts.
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