Table of Contents:
[ Alcohol
/ Caffeine / Tobacco ]
[ Cocaine / Marijuana
/ Heroin ]
What is the history of caffeine and xanthine use?
Caffeine use (and use of related substances) dates back to the
Stone Age. It is believed that paleolithic man discovered caffeine
containing plants throughout the world. The raw fruit of the
coffee plant (Coffea arabica) was used to prepare beverages.
The raw fruit was later replaced by roasted coffee beans. Coffee
was introduced from Turkey to Europe via Venice. The French
claimed that coffee could be used to treat small pox, gout,
and scurvy. The English claimed that coffee could cure venereal
diseases, indigestion and common cold. At least half of the
world's population consumes tea which contains small amounts
of theophylline and caffeine prepared from the leaves of Thea
sinensis which is a bush native to China and cultivated in many
other countries.
Cocoa and chocolate are derived from the seeds
of Theobroma coca, which contain theobromine and some caffeine.
The basis for the popular use of caffeine containing products
grew from the belief that these products had stimulant actions
that elevated mood, decreased fatigue, and increased capacity
for work. Classic pharmacological studies have confirmed these
beliefs.
What is the chemistry of caffeine and other xanthines?
Caffeine is one member of the group called xanthines. The other
xanthines are theophylline and theobromine. Caffeine is found
in 63 species of plants.
Caffeine, theophylline and theobromine are all
called methylated xanthines and are usually referred to as xanthine
derivatives, methylxanthines or, xanthines.
How are caffeine and other xanthines processed in the
body?
Caffeine is absorbed in the body almost 100%. After oral administration
caffeine appears in the blood in about 5 minutes after ingestion.
Peak plasma concentrations usually occur in 15-120 minutes after
ingestion. Caffeine is absorbed more slowly from soft drinks
than from tea or coffee. Caffeine is rapidly distributed to
the tissues from plasma into the brain by simple diffusion.
Caffeine is broken down by the liver and eliminated in the urine.
About 0.5 to 3.5% of the caffeine consumed is excreted chemically
unchanged, in the urine. The plasma half-life of caffeine varies
from 3 to 5 hours. Moderate exercise seems to increase peak
plasma concentrations of caffeine. Smoking increases caffeine
removal from the plasma by increasing metabolic rate. Oral contraceptives
and alcohol reduce caffeine metabolism and raise its plasma
levels.
Effects of methyxanthines on the circulatory system
are complex and sometime antagonistic. The effects depend on
the conditions at the time of administration, and the dosage
used. Caffeine and theophylline have powerful effects on the
circulatory system. Theophylline decreases the peripheral vascular
resistance, and has a powerful cardiac stimulation effect. Xanthines
also cause a significant increase in cerebrovascular resistance
with a decrease in blood flow and in the oxygen tension of the
brain.
Xanthines relax smooth muscles of the bronchi.
Theophylline is the most effective and produces a definite increase
in vital capacity. Theophylline is used in the treatment of
bronchial asthma. Xanthines increase the production of urine.
The pattern of enhanced excretion of water and
electrolytes are very similar to the effects of thiazide diuretics.
What are the effects of caffeine and other xanthines
on the central nervous system?
Xanthines stimulate the central nervous system. Traditionally
caffeine was considered the most potent methylxanthine; however,
theophylline produces a more profound CNS stimulation action
than caffeine. Caffeine effects the central nervous system in
doses ranging from 85 to 250 mg; the amount contained in 1 to
3 cups of coffee. Many individuals use caffeine to reduce drowsiness
and fatigue, improve mood, alertness and productivity. Caffeine
increases capacity for sustained intellectual effort with clearer
flow of thought. Doses above 250-mg methylxanthines produce
nervousness, insomnia, restlessness, and tremors. At higher
doses focal and generalized convulsions have been observed.
What are the clinical uses of caffeine and other xanthines?
Caffeine has been used in a number of over the counter analgesic
drugs. Caffeine may be used topically for dermatitis. Theophylline
preparations are used to relax bronchial smooth muscle for asthma
and chronic obstructive pulmonary disease.
What are the adverse effects associated with the use
of caffeine and other xanthines?
Student athletes who use large amounts of caffeine may experience
nervousness, irritability, insomnia, increased heart beat, hypertension,
gastric distress, peptic ulcer, delirium, seizures, coma, and
increased serum cholesterol.
What are the effects of caffeine on athletic performance?
Some studies have reported that long term endurance exercise
has been shown to be positively enhanced by caffein. Caffeine
has been found to have no significant effect on high intensity,
short-term work. Reports on caffeine's effect on VO2 max are
inconsistent. The delay in the onset of fatigue is attributed
to the sparing of muscle glycogen and to caffeine's lipolytic
effect, or ability of the body to release more fat for energy.
Coordination and other fine motor skills are not enhanced or
diminished following caffeine ingestion. The NCAA limit for
caffeine in a urine specimen is 15 micrograms per ml. Two cups
of black coffee will yield urine levels of approximately 3 to
6 micrograms per ml.
For more information on caffeine use visit
the NCAA web site.
