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Caffeine; Facts
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<h1>Facts about: caffeine</h1>
bitter-tasting, crystalline
substance was first isolated from
coffee in 1820. Both words, caffeine and coffee, are
derived from
the Arabic word qahweh (pronounced "kahveh" in Turkish). The
origins of the words reflect the spread of the beverage into
Europe via
Arabia and Turkey from north-east Africa, where coffee
trees were cultivated in the 6th
century. Coffee began to be
popular in Europe in the 17th century. By the 18th
century
plantations had been established in Indonesia and the West
Indies.
<p>
The caffeine content of coffee beans varies according to the
species of the coffee plant. Beans from Coffea arabica, grown
mostly in
Central and South America, contain about 1.1% caffeine.
Beans from Coffea robusta,
grown mostly in Indonesia and Africa,
contain about 2.2% caffeine. Caffeine also occurs
in cacao pods
and hence in cocoa and chocolate products; in kola nuts, used in
the preparation of cola drinks; and in the ilex plant, from whose
leaves the
popular South American beverage yerba mate is
prepared.
<p>
Caffeine is also found in tea. It was first isolated from tea
leaves in 1827
and named "theine" because it was believed to be a
distinctly different
compound from the caffeine in coffee. Tea
leaves contain about 3.5% caffeine, but a cup
of tea usually
contains less caffeine than a cup of coffee because much less tea
than coffee is used during preparation.
<p>
In North
America, the caffeine content of a cup of coffee
averages about 75 mg, but varies
widely according to cup size,
the method of preparation, and the amount of coffee
used.
Generally, cups prepared from instant coffee contain less
caffeine
(average 65 mg) and cups prepared by drip methods
contain more caffeine (average 110
mg). Cups of tea average about
30 mg, but the range is also largeþfrom 10 to 90 mg.
<p>
Cola drinks contain about 35 mg caffeine per standard 280 mL
serving, with some 5% of the caffeine being a component of kola
nuts and most
of the remainder being added in the form of a
by-product of the decaffeination of
coffee and tea. Caffeine-
containing soft drinks account for more than 65% of soft
drink
consumption. A cup of hot chocolate contains about 4 mg caffeine,
and a 50-gram chocolate bar between 5 and 60 mg, increasing with
the quality of the
chocolate. Caffeine is an ingredient of
certain headache pills (30-65 mg). It is the
main ingredient of
non-prescription "stay-awake" pills (100-200 mg).
<p>
<h2>Short-term Effects</h2>
Caffeine taken in beverage form begins to reach all tissues of
the body within five
minutes. Peak blood levels are reached in
about 30 minutes. Half of a given dose of
caffeine is metabolized
in about four hours þ more rapidly in smokers and less rapidly
in
newborn infants, in women in late pregnancy, and in sufferers
from
liver disease. Normally, almost all ingested caffeine is
metabolized. Less than 3%
appears unchanged in urine, and there
is no day-to-day accumulation of the drug in the
body.
<p>
Short-term effects of a drug are those that appear soon
after a
single dose and disappear within hours. Ingestion of the amount
of
caffeine in one or two cups of coffee (75-150 mg) causes many
mild physiological
effects. General metabolism increases -
expressed as an increase in activity or raised
temperature, or
both. The rate of breathing increases, as does urination and the
levels of fatty acids in the blood and of gastric acid in the
stomach.
(However, at least one other component of coffee also
increases gastric acid secretion.
Therefore ulcer sufferers may
not achieve relief by switching to decaffeinated coffee.)
<p>
Caffeine use may increase blood pressure.
<p>
Caffeine stimulates the brain and behavior. Use of 75-150 mg of
caffeine
elevates neural activity in many parts of the brain,
postpones fatigue, and enhances
performance at simple
intellectual tasks and at physical work that involves
endurance
but not fine motor coordination. (Caffeine-caused tremor can
reduce hand steadiness.)
<p>
Caffeine’s effects on complex
intellectual tasks and on mood do
not lend themselves to a simple summary. The effects
depend on
the personality of the user, on the immediate environment, on the
time of day.
<p>
The effects of caffeine on sleep are clear-cut: taken before
bedtime, it usually delays sleep onset, shortens overall sleep
time, and
reduces the "depth" of sleep. After using caffeine,
sleepers are more easily
aroused, move more during sleep, and
report a reduction in the quality of sleep. The
effects of
caffeine on dreaming are less clear.
<p>
Larger doses of caffeine, especially when given to non-users, can
produce headache,
jitteriness, abnormally rapid heartbeat
(tachycardia), convulsions, and even delirium.
Near-fatal doses
cause a crisis resembling the state of a diabetic without
insulin, including high levels of blood sugar and the appearance
of acetone-like
substances in urine.
The lowest known dose fatal to an adult has been 3,200 mg -
administered intravenously by accident. The fatal oral dose is in
excess of
5,000 mg - the equivalent of 40 strong cups of coffee
taken in a very short space of
time.
<p>
<h2>Tolerance and
dependence</h2>
Tolerance refers to the body’s "getting used" to a drug with
its
repeated taking. It is difficult to study the tolerance of human
subjects to the various effects of caffeine because nearly
everyone in our society uses
caffeine regularly in one form or
another. Careful research has suggested that
tolerance develops
to most of caffeine’s effects - meaning that, with experience of
the drug, the same dose produces a reduced effect, or a larger
dose is
required to produce the same level of effect.
<p>
Regular use of
upwards of 350 mg of caffeine a day causes
physical dependence on the drug. This means
that interruption of
the regular use produces a characteristic withdrawal syndrome,
the most conspicuous feature of which is an often severe headache
that can be
relieved by taking caffeine. Absence of caffeine also
makes regular users feel
irritable and tired. Relief from these
withdrawal effects is often given as a reason
for using caffeine.
<p>
<h2>Long-term
Effects</h2>
Long-term effects of a toxic nature do not appear evident when
regular caffeine use is below about 650 mg a day - equivalent to
about eight or nine
average cups of coffee. Above this level,
users may suffer from chronic insomnia,
persistent anxiety and
depression, and stomach ulcers. Caffeine use appears to be
associated with irregular heartbeat and may raise cholesterol
levels, but
there is no firm evidence that caffeine causes heart
disease.
<p>
The evidence is also unclear concerning caffeine and cancer.
Caffeine and
some of its metabolites can cause changes in the
cells of the body and in the way in
which they reproduce
themselves, and caffeine certainly enhances this kind of action
by some known carcinogens. However, although caffeine is
suspected as a cause
of cancer, the evidence is contradictory and
does not allow a clear conclusion. Some
animal studies suggest
that caffeine can have anti-cancer properties. For example,
in
rats it prevents breast cancer caused by diethylstilbestrol (the
"morning after" pill).
<p>
Caffeine certainly has the
ability to cause a variety of
reproductive effects in animals, including congenital
abnormalities and reproductive failures, reduced fertility,
prematurity, and
low birth weight. What is unknown is whether
these findings are relevant to the use of
ordinary amounts of
caffeine-containing beverages by pregnant women. Pregnant women
have been advised to restrict caffeine intake by both Canadian
and United
States governments. Pregnant smokers should be
especially wary.
<p>
<h2>Therapeutic uses</h2>
The most common medicinal
use of caffeine is as a part of
headache preparations and other pain relievers.
Caffeine is added
both for its specific ability to relieve headache, including that
caused by caffeine withdrawal, and for its ability to help
analgesics do
their work better.
<p>
The ability of caffeine to stimulate
breathing is used in the
treatment of apnea (cessation of breathing) in newborn
babies,
and as an antidote against the depression of breathing by
overdoses of heroin and other opiate drugs.
<p>
More controversial
therapeutic uses of caffeine are these: to
kill skin funguses; to improve sperm
mobility; to enhance the
toxic effects of chemicals used in cancer therapy; and to
facilitate the production of seizures during electroconvulsive
therapy.
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Revised January 1991
Alcoholism and Drug Addiction Research
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