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COFFEE AND CAFFEINE:
The amount of caffeine in a cup of coffee can vary
greatly, depending on its origin or the composition of the blend, the
method of brewing and the strength of the brew. Instant, or soluble, coffee
generally contains less caffeine than roast and ground coffee, but may be
consumed in greater volume. Robusta coffees have about twice as much
caffeine as Arabica. A 'cup' is usually understood to contain 150 ml (5 oz
in the United States)
but an espresso may be as small as 40 ml. The U.S. Food and Drug
Administration gives the following ranges for caffeine contents:
Type
|
range
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average
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Roast and ground
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drip method
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60-180
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115
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percolator
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40-170
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80
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Instant
coffee
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30-120
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65
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(mg per 5 oz cup)
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Consumer
surveys
An interesting
survey of caffeine contents in cups of coffee was conducted in Canada
(Stavric et al, reference below). Whether the coffee was prepared by
housewives at home, for sale in commercial outlets, or by individuals at
work, the mean caffeine content was about 80 mg per cup (about 350 mcg per
ml). The means for roast and ground coffee, both drip and percolator
brewed, were below 85 mg; for instant coffee 71 mg. However, the range of
measurements was so wide that, for most individuals, it would be inaccurate
to use these figures as a basis for calculating the exact amount of
caffeine consumed in a day. The size of the cup/serving varied from 25 ml
(Greek coffee) to 330 ml at home and from 130 ml to 280 ml in the
out-of-home situation.
DECAFFEINATED
COFFEE
Whatever method of decaffeination is used, the decaffeinated green coffee
must contain less than 0.1 % caffeine (dry weight basis) to comply with EC
regulations. This corresponds to about 3mg caffeine in a cup of
decaffeinated coffee.
OTHER
BEVERAGES
Tea contains more caffeine than coffee weight for weight, but less weight
is used, in general, to brew a cup of tea. In the Canadian study referred
to above, both the type of tea used and the steeping time affected the
caffeine concentration of samples prepared in the laboratory as follows:
|
2 minutes
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5 minutes
|
Tea-bag
|
238
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402
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Loose tea
|
189
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295
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( Mean, mcg per ml)
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The average caffeine concentration of samples of tea prepared at home was
lower, at 159 mcg per ml, but with a wide variation. The caffeine content
of a cup of tea is usually less than 60 mg, but a strong cup of tea may
contain more caffeine than a weak cup of regular coffee. Cocoa and
chocolate drinks contribute 4-Smg caffeine per cup to the diet, dark
chocolate and cooking chocolate 20-26mg per ounce (0.7-0.9mg per gram).
Many soft drinks, including colas and "peppers", contain
caffeine, which as well as being present in cola nuts is often added as a
flavour ingredient. A 12-ounce serving may contain 30-60mg caffeine. The
major brands of cola on sale in the UK contain about 120mg caffeine
per litre.
DRUGS
Caffeine is present in many prescription and non-prescription
(over-the-counter) drugs, including some taken for headache, pain relief,
appetite control, staying awake, colds, asthma and fluid retention. The
caffeine content of drugs varies from 7mg to 200mg per tablet.
LEVELS OF
CAFFEINE CONSUMPTION
Caffeine is generally consumed in amounts less than 300mg per day, roughly
equivalent to: 3-4 cups of roast and ground coffee 5 cups of instant coffee
5 cups of tea 6 servings of some colas or 10 tablets of some painkillers It
has been suggested that the British consume more caffeine on average than
Americans, but there are no large scale studies to support the observation.
The nine, normal subjects recruited by Dr M.S. Bruce and his colleagues, as
habitual caffeine users, for a study in London (reference below) were found
to consume on average 428mg caffeine a day, with a range from 230mg to
670mg. Customary caffeine consumption has been classified as follows: Low
caffeine users: less than 200mg per day Moderate caffeine users: 200-400mg
per day High caffeine users: more than 400mg per day References Bruce M.S.
et al. British Journal of Clinical Pharmacology,22: 81-87. 1986. Lecos C.
The latest caffeine scorecard. FDA Consumer, March 1984. Stavric B. et al.
Variability in caffeine consumption from coffee and tea: possible
significance for epidemiological studies. Fd Chem Toxic 26(2):111-118.
1988.
A SUMMARY OF
THE PHYSIOLOGICAL EFFECTS OF CAFFEINE
Soon after
drinking a cup of coffee, or tea or cola, caffeine is distributed
throughout the body. As it is similar to substances normally present in the
tissues, caffeine could affect all the systems of the body: nervous,
cardiovascular, respiratory and so on. However, caffeine does not
accumulate in the body, so its effects are short-lived and transitory.
Whether or not caffeine's effects are physiologically important (or even
noticeable) depends on a number of factors. Every individual reacts
differently to caffeine. For example, caffeine may stay in the body of
pregnant women for up to 3 times as long as is usual in adults, whereas
smokers eliminate caffeine twice as quickly as non-smokers. This may help
to explain why women often feel more sensitive to coffee in the latter
stages of pregnancy, or why heavy smokers are usually heavy coffee drinkers
as well. Some of the effects of caffeine, such as those on the heart and
blood vessels, are contradictory and have no net effect - others may only
be noticeable when regular consumers suddenly cut out caffeine. The body
can become habituated to caffeine so that regular users are less sensitive
to the stimulant effects than others. In fact, people tend to regulate
their coffee consumption according to their experience - as many cups of
coffee in the morning as they find give a pleasant, stimulating effect -
perhaps none a few hours before going to bed. Of all the physiological
effects of coffee, the best known is that it is a stimulant to the nervous
system. One or two cups of coffee can make one feel more awake, alert and
able to concentrate. Caffeine has been shown to counteract fatigue and
restore flagging performance. However, in sensitive individuals, caffeine
may delay the onset of sleep, decrease sleep time and even lower the
subjective quality of the sleep. Caffeine has various effects on mood,
ranging from pleasant stimulation and mood elevation to anxiety,
nervousness and irritability, but these are transient and dose-related.
Other physiological effects of caffeine, in the short term, include
increases in blood pressure, plasma catecholamine, plasma rennin and serum
free fatty acids; the production of urine and of gastric acid are also
increased. Regular consumption in normal individuals rapidly leads to
tolerance and has no adverse effects. The vast bulk of scientific and
epidemiological evidence points to the conclusion that normal, regular
consumption of coffee and caffeine containing beverages is not associated
with heart or cardiovascular diseases, damage to the foetus, benign breast
disease or cancer of any kind. Some people with irregular heartbeat
syndromes may choose to drink decaffeinated coffee since caffeine has been
known to precipitate arrhythmias or ventricular premature beats, as do
alcohol, exercise, stress and many drugs. Standard reference Evaluation of
Caffeine Safety, a scientific status summary by the Institute of Food
Technologists' Expert Panel on Food Safety
and Nutrition, 1987. Food Technology, Institute
of Food Technologists, Chicago,
41(6):105-113.June 1987
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