is caffeine a health hazard

8/4/2019 Is Caffeine a Health Hazard

1/14

Is Caffeine a Health Hazard?

by Ben Best

CONTENTS: LINKS TO SECTIONS BY TOPIC

I. CAFFEINE BEVERAGES

II. CAFFEINE CHEMISTRY

III. CAFFEINE ACTION ON ADENOSINE RECEPTORS

IV. SLEEP, ADENOSINE AND CAFFEINE

V. ADENOSINE, CAFFEINE AND ISCHEMIA/HYPOXIA

VI. HEART DISEASE, CANCER AND CAFFEINE

VII. OTHER EFFECTS OF CAFFEINE

I. CAFFEINE BEVERAGES

Caffeine is the most widely consumed drug in the world, most commonly from the beverages

coffee, tea and soda. An estimated 80% of the world's population consumes a caffeine-

containing substance daily. A typical 8-ounce (240-ml) cup of instant coffee contains about

100 mg of caffeine about twice as much as a cup of tea or a 12-ounce (360-ml) can/bottle

of soda. A 30-gram chocolate bar might contain as much caffeine as half a cup of tea. Pure

caffeine can be obtained in powders, caplets or tablets in products like NoDoz.

The English word caffeine comes from the French (Spanish & Portugese) word forcoffee:

caf. Caffeine has been identified in over a hundred species of plant, but the most highly

cultivated sources are the seeds (beans) of the berries from the coffee tree(Coffea arabica or

Coffea canephora, variety robusta), the leaves & leaf-buds of the tea bush (Thea sinensis,also known as Camellia sinensis), the nut of the kola tree (Cola acuminata) and the seeds

(beans) of the fruit from the cacao (cocoa) tree (Theobroma cacao). Why caffeine is found in

so many plants is a matter of speculation, but a popular theory is that caffeine functions as a

natural pesticide insofar as caffeine is lethally toxic for the larvae of mealworms, mosquitos

and tobacco hornworms, among others.

The medicinal use of coffee by Islamic physicians probably began before the second

Millennium A.D. The first documented use of coffee as a beverage was by the Sufis of

Yemen, who were using the drink to stay awake during prayers in the mid-1400s. By 1510

there were coffeehouses in Mecca & Cairo. As coffeehouses spread throughout the Islamicworld, their reputation for becoming places for gaming, secular music, vice and seditious

political & religious discussion led to periodic prohibitions as well as debates over

whether the KORAN approves of coffee.

Although the first coffeehouses opened in England in the 1650s and in Holland a decade

later, the first Parisian caf (coffeehouse) did not open until 1689. The Dutch introduced the

coffee plant to the island of Java in 1688. The island's association with coffee production led

to the use of "Java" as a nickname for high quality coffee.

Brewing is the process of extracting coffea from the bean into water. Instant coffee is pre-

brewed in large quantity and then dried to preserve flavor. Most of the water can be removed
http://www.benbest.com/health/caffeine.html#beverageshttp://www.benbest.com/health/caffeine.html#chemistryhttp://www.benbest.com/health/caffeine.html#adenosinehttp://www.benbest.com/health/caffeine.html#sleephttp://www.benbest.com/health/caffeine.html#ischemiahttp://www.benbest.com/health/caffeine.html#cancerhttp://www.benbest.com/health/caffeine.html#otherhttp://www.nwlink.com/~donclark/java/world.htmlhttp://www.nwlink.com/~donclark/java/world.htmlhttp://www.benbest.com/health/caffeine.html#chemistryhttp://www.benbest.com/health/caffeine.html#adenosinehttp://www.benbest.com/health/caffeine.html#sleephttp://www.benbest.com/health/caffeine.html#ischemiahttp://www.benbest.com/health/caffeine.html#cancerhttp://www.benbest.com/health/caffeine.html#otherhttp://www.nwlink.com/~donclark/java/world.htmlhttp://www.benbest.com/health/caffeine.html#beverages


2/14

by evaporation, but the residual water is more difficult to remove. Freeze-drying preserved

the flavor better than drying at high temperature.

In 1903 an Italian manufacturer who was impatient with the amount of time his employees

spent brewing coffee during coffee breaks invented a machine that used high temperature &

pressure to rapidly extract coffee from grind. The result was espresso (Italian forfast).Coffee connoisseurs regard espresso to be "coffee at its very best". Modern espresso

machinesforce nearly-boiling water through finely powdered blends of coffee at pressures of

up to 15 atmospheres in less than half-a-minute. The result is an ounce-and-a-half of syrupy,

fragrant, richly-flavored coffee emulsified in natural fats & colloids containing about half

as much caffeine as an 8-ounce cup of brewed coffee. Espresso topped with equal parts of

foamed & steamed milk is called cappuccino.

Until the end of the 17th century most coffee was produced in Yemen. By the 1950s Brazil

was producing half the world's coffee and it remains the leading producer. Decaffeination of

coffee began early in the 20th century. By 1985 nearly one-fifth of coffee-drinkers were

consuming decaf, but the percentage dropped thereafter. There is no truth to the claim thatdecaf contains residual solvents (the newer methods of producing decaf use high-pressure

carbon dioxide). The caffeine removed from decaf coffee is used for making soda drinks.

Tea cultivation is believed to have begun in the Szechwan province of China a few centuries

before the Common (Christian) Era after the Chinese learned of the plant's use by natives of

northern India or Southeast Asia. Buddhist priests brought tea-drinking from China to Japan

in the 6th Century A.D. The word tea in most languages traces from Chinese roots. In the

17th century the English East India Company became the world's foremost tea monopoly.

Bitter feelings among Americans culminating in the Boston Tea Party may partially account

for the fact that the English consume far more tea than Americans and Americans

consume far more coffee than the English.

Tea contains both caffeine and tannins. Tannin (which converts rawhide into leather) is an

astringent used in folk remedies for diarrhea, bleeding, inflammation and skin eruptions. Teas

may be fermented (black tea), unfermented (green tea) or partially fermented (oolong).

Fermenting reduces astringency, while changing color & flavor. Green tea retains

polyphenols which help prevent cancer, while containing less caffeine than regular (black)

tea.

Use of the cacao (cocoa) bean for a beverage originated with the Indians of South America,

possibly earlier than 1,000 B.C. The Spanish were introduced to the drink by the Aztecs. Insixteenth century Spain a sugared chocolate drink was consumed in a form that was strong

enough to manifest the stimulant properties of caffeine & theobromine. In 1828 a Dutch

chemist devised a means to remove most of the bitter fat from cocoa, neutralize the acids and

create a water-soluble powder. In 1875, Henri Nestl of Switzerland (inventor of condensed

milk) helped create the first milk chocolate. As of the year 2000, Switzerland had the highest

per capital chocolate consumptionin the world nearly twice that of the United States.

In 1886 the Georgia pharmacist John Pemberton created a beverage flavored by caffeine-

containing kola nuts and fortified by cocaine from the coca plant (Erythroxylum coca) of Peru

& Bolivia. He called his beverage Coca-Cola in honor of the plants of origin. Near the turn

of the century cocaine was removed from Coca-Cola and replaced with more caffeine.(Lithium carbonate currently used as a treatment for mania was not removed from 7-
http://home.howstuffworks.com/espresso-machine.htmhttp://home.howstuffworks.com/espresso-machine.htmhttp://home.howstuffworks.com/espresso-machine.htmhttp://www.candyusa.org/Stats/chocolateworld.shtmlhttp://www.candyusa.org/Stats/chocolateworld.shtmlhttp://home.howstuffworks.com/espresso-machine.htmhttp://home.howstuffworks.com/espresso-machine.htmhttp://www.candyusa.org/Stats/chocolateworld.shtml


3/14

Up until a half-century later.) A 12-ounce (360-ml) container of Coca-Cola, Pepsi-Cola,

Dr. Pepper, Tab, Mr Pibb, Mountain Dew and many other soft drinks contains as

much caffeine as a cup of tea. Jolt, which has as much caffeine as a cup of coffee, is

promoted as having "twice the sugar" and "twice the caffeine of other colas".

For the caffeine content of common beverages seeCaffeine Content of Foods and Drugs orCaffeine Content of Beverages, Foods and Drugs.

The Scandinavian countries (Sweden, Norway & Denmark) and the Netherlands have the

highest per-capita caffeine consumption in the world about 400 milligrams per person per

day, mostly from coffee. Caffeine consumption in the US, Canada and the UK is about half

that amount mostly from coffee in North America. In the UK slightly more caffeine comes

from tea than from coffee, which means drinking many cups of tea to compensate for the

lower caffeine content of the tea. Only in Ireland & Kuwait is the tea consumption higher

than in the UK.

In the United States coffee consumption increases with higher education & income and isparticularly high for Roman Catholics. Claims that coffee-drinking correlates with higher

intelligence cannot be taken as proof that caffeine increases intelligence or that drinking

coffee is smart. Lower incidence ofAlzheimer's Disease (AD) among coffee-drinkers could

easily be a consequence of the negative correlation between level of education & AD and the

positive correlation between level of education & coffee-drinking rather than evidence that

caffeine prevents AD.

(return to contents)

II. CAFFEINE CHEMISTRY
http://www.cspinet.org/new/cafchart.htmhttp://www.cspinet.org/new/cafchart.htmhttp://www.holymtn.com/tea/caffeine_content.htmhttp://www.holymtn.com/tea/caffeine_content.htmhttp://www.benbest.com/lifeext/Alzheimer.htmlhttp://www.benbest.com/health/caffeine.html#contentshttp://www.cspinet.org/new/cafchart.htmhttp://www.holymtn.com/tea/caffeine_content.htmhttp://www.benbest.com/lifeext/Alzheimer.htmlhttp://www.benbest.com/health/caffeine.html#contents


4/14

Chemically, caffeine is 1,3,7-

trimethylxanthine meaning

it is a xanthine molecule with

methyl groups replacing all of

the three hydrogens bound to

nitrogens in the xanthine ring.Caffeine is metabolized

(demethylated) in the liver by CYtochrome P450 enzymes known as 1A2 (orCYP1A2). The

first products of metabolism are all dimethylxanthines: paraxanthine (84% 1,7-

dimethylxanthine), theobromine (12% 3,7-dimethylxanthine), and theophylline (4% 1,3-

dimethylxanthine). The half-life for caffeine metabolism is typically 5-6 hours in an adult.

Theophylline relaxes smooth muscles of the bronchi and has been used for this purpose in

the treatment of asthma. Theobromine from the cocao tree (Theobroma cacao), contains no

bromine and is the principal alkaloid in cacao. Theobromine is a diuretic (increases urine

production) that can dilate blood vessels and reduce blood pressure. By weight, chocolate is

about 2.2% theobromine & 0.1% caffeine, but caffeine is seven times more potent than

theobromine.

In the body, xanthine is a breakdown product ofadenine & guanine, the two purine baseswhich are key constituents of DNA & RNA. Adenine is also the purine base in the energy-


5/14

storage molecule ATP (Adenine TriPhosphate) and the second-messengermolecule cAMP

(cyclic Adenosine MonoPhosphate). Adenine can be deaminated in the body to

hypoxanthine, oxidized to xanthine and oxidized again to uric acid for excretion. Uric acid

also has anti-oxidant properties which may help to account for the long lifespans of birds &

humans but uric acid can lead to gout. Rather than being oxidized, hypoxanthine can be

recycled to form more AMP, GMP or nucleic acids.

Adenosine is an adenine molecule attached to a ribose or deoxyribose sugar molecule. The

similarity in chemical structure between the adenine portion of adenosine and the caffeinemolecule is the key to how caffeine works. Cells including neurons have adenosine

receptors. Adenosine acts as a neurotransmitter in the brain, but is not released from

synapses. The caffeine molecule is similar enough to adenine to fit into adenosine receptors,

but is not similar enough to stimulate those receptors. So the main action of caffeine is to

block adenosine receptors. Ethanolexerts many of its effects by modifying adenosine

receptor activity.

Adenosine cyclic AMP
http://www.benbest.com/science/anatmind/anatmd1.html#synapseshttp://www.benbest.com/lifeext/aging.htmlhttp://www.benbest.com/lifeext/aging.htmlhttp://www.benbest.com/health/alcohol.htmlhttp://www.benbest.com/health/alcohol.htmlhttp://www.benbest.com/science/anatmind/anatmd1.html#synapseshttp://www.benbest.com/lifeext/aging.htmlhttp://www.benbest.com/lifeext/aging.htmlhttp://www.benbest.com/health/alcohol.html


6/14

Cyclic AMP (cAMP, cyclic Adenosine MonoPhosphate) acts as a cellular signalling

molecule which transmits signals from the cell membrane to the interior of the cell and to the

nucleus. Cyclic AMP is quickly metabolized by phosphodiesterases, ie, by enzymes which

break the diester bond (two oxygen bonds) connecting the 5' carbon to the 3' carbon of theribose between the phosphate forming the cycle. Caffeine is similar enough to adenine that it

binds to phosphodiesterases, and it can inhibit phosphodiesterase molecules preventing them

from hydrolyzing (inactivating) cAMP. Practically speaking, however, this effect occurs only

modestly in the body because the amounts required for a significant effect are greater than the

plasma levels of caffeine acheived by coffee-drinking.


III. CAFFEINE ACTION ON ADENOSINE RECEPTORS

More than 99% of orally

ingested caffeine is absorbed

with peak plasma levels

obtained in 15 to 45 minutes.

Caffeine is soluble in both

water & oil and can readily

cross the blood-brain barrier.Caffeine potentially has

pharmacological actions other

than blockage of adenosine

receptors, but it requires

20 times as much caffeine to

inhibit phosphodiesterase,


blockGABAA receptors and


mobilize intracellular calcium

as is required to blockadenosine receptors. Caffeine
http://www.benbest.com/health/caffeine.html#contentshttp://www.benbest.com/science/anatmind/anatmd10.html#gabahttp://www.benbest.com/health/caffeine.html#contentshttp://www.benbest.com/science/anatmind/anatmd10.html#gaba


7/14

acts primarily by the direct action of blocking adenosine receptors and by the indirect action

upon the receptors forneurotransmitters.

Adenosine is a neuromodulator, not a neurotransmitter . Adenosine is not stored in vesicles

nor released as a bolus in response to depolarization of a presynaptic membrane. Instead,

adenosine accumulates in extracellular fluids as a result of cell physiology and is thereforereleased from both neurons and glial cells. Adenosine is produced as a by-product ofATP

(Adenosine TriPhosphate, the energy source for cellular metabolism) utilization.

Adenosine actions on adenosine receptors inhibit the release of neurotransmitters. Adenosine

receptors are classified as A1, A2A, A2B and A3, although only the first two are of significance

for neurotransmitters because A2B & A3 subtypes are mainly located in peripheral tissues

outside the brain. Accumulation of adenosine at A1 receptors on presynaptic membranes

inhibits the release of most brain neurotransmitters, including glutamate, GABA,

norephinephrine, serotonin and acetylcholine the strongest action being inhibition of

glutamaterelease. A1 receptors have highest abundance in the brain concentrated in the

cerebral cortex, hippocampus, cerebellum and the reticular formation of the spinal cord.

Adenosine A1 receptors in the brain are mostly located presynaptically on axons. A1 receptors

inhibitthe enzyme adenylyl cyclase, decreasing cAMP levels although significant

physiological action from this effect has not been observed. A1 receptors block presynaptic

calcium channels and activate potassium channels (causing hyperpolarization). Adenosine A2receptors activate adenylyl cyclase, converting ATP into the second messenger cAMP

which can inhibit L-type & N-type calcium channels. In the brain, the effects of A 1 receptors

greatly predominate over those of the A2A receptors both because A1 receptors are more

numerous and because adenosine has a higher affinity for A1 receptors [EUROPEAN

JOURNAL OF PHARMACOLOGY 365:9-25 (1999)].

A1 adenosine receptors inhibit neural activity by both pre-synaptic and post-synaptic

mechanisms. Pre-synaptic blockage of N-type calcium (Ca2+) channels reduces

neurotransmitter release. Post-synaptically A1 receptor stimulation causes both enhanced

Cl- influx (in a GABA-independent manner) and enhanced K+ influx both of which inhibit

depolarization.

Adenosine stimulates and caffeine blocks all classes of adenosine receptors nonselectively.

The general effect of adenosine in the brain is to inhibit neural activity, whereas the general

effect of caffeine is to increase neural activity.
http://www.benbest.com/science/anatmind/anatmd10.htmlhttp://www.benbest.com/science/anatmind/anatmd10.html#glutamatehttp://www.benbest.com/science/anatmind/anatmd10.html#glutamatehttp://www.benbest.com/science/anatmind/anatmd10.htmlhttp://www.benbest.com/science/anatmind/anatmd10.html#glutamate


8/14

(A general increase in neural activity is not necessarily a good thing in the worst case

general stimulation results in an epileptic spasm, rather than the controlled activity of thought

& learning.Neurons need to rest to work effectively. Caffeine disrupts the time neurons work

and rest.)

Adenosine A2A receptors areprominent in endothelial cells,

resulting in the vasodilation

effect of adenosine (and the

vasoconstrictive effect of

caffeine on cerebral blood

vessels sometimes used to

treat migraine headache). In

the brain, only the A2A subtype

of A2 receptors have

significant activity, and these

are primarily located in thedopamine-rich areas of the

basal ganglia controlling

locomotion. A2A receptor

activity inhibits locomotor

activity in part by inhibiting

dopamine action at D2receptors. Adenosine A2Areceptors in the hippocampus

are of more prominence than the illustration indicates, and adenosine action on those

receptors facilitate hippocampal glutamatergic synapse transmission by opposing the tonic

inhibition due to adenosine at A1 receptors [NEUROSCIENCE 112(2):319-329 (2002)],

although the adenosine A1 receptor effect predominates.

Caffeine's antagonism of adenosine action on A2A receptors in the globus pallidus decreases

release of the inhibitory neurotransmitter GABA (Gamma-AminoButyric Acid). Caffeine

can neutralize the effects of benzodiazepine tranquilizers such as diazepam (Valium).

Benzodiazepines act by enhancing the effect of GABA on GABAA receptors, whereas

caffeine has an opposite effect by inhibiting GABA release. Unlike cocaine, amphetamine,

morphine, alcohol and nicotine, caffeine does not activate dopamine release (to D2 receptors),

in the "pleasure centers" (the shell) of the nucleus accumbens, which are associated with

addiction. The "addictive" properties of caffeine seem to be almost entirely connected towithdrawal symptoms.
http://www.benbest.com/science/anatmind/anatmd10.html#gabahttp://www.benbest.com/science/anatmind/anatmd10.html#gaba


9/14

Experiments on mice may give an indication of the effects of chronic caffeine administration.

The density of cortical A1 adenosine receptors increased 20% whereas the density of A2Areceptors in the basal ganglia did not change. Densities of cortical serotonin receptors

increased by 26-30%, cortical cholinergicreceptor densities increased 40-50% and cortical

GABAA receptor densities increased 65%. Cortical & cerebellaradrenergic receptor densities

decreased by 25% [CELLULAR AND MOLECULAR NEUROBIOLOGY 13(2):247-261(1993)].

Adenosine typically

accumulates in the

extracellular space during

conditions of fatigue ie,

when the rate of ATP

utilization exceeds the rate of

ATP synthesis. Adenosine

accumulates in the forebrain &

hippocampus during sustainedwakefulness (promoting

sleepiness) and decreases

during sleep. During seizures,

hypoxia or ischemia,

accumulation of adenosine

may be very rapid. In the heart,

hypoxia dramatically reduces

adenosine kinase activity,

which also promotes adenosine

accumulation. Adenosine can

be increased by high levels of

S-AdenosylHomosysteine (SAH) or reduced by an excess of L-homocysteine.


IV. SLEEP, ADENOSINE AND CAFFEINE

Two physiologically distinctphases of sleep are distinguished: REM (Rapid Eye Movement)

and non-REM sleep. REM sleep is distinguished from non-REM sleep by brain electrical

activity comparable to that seen in wakefulness as well as by higher blood pressure & oxygenconsumption. About three-quarters of sleep time is spent in non-REM. Sleep normally begins

with non-REM sleep, which progresses from stages I & II (light non-REM sleep) to

stages III & IV (deep non-REM sleep). About half of non-REM sleep is spent in stage II, the

deeper stage of light sleep. In a typical night's sleep of 8 hours a normal person will go

through about 5 cycles of alternating non-REM & REM sleep lasting over 90 minutes per

cycle.

Brain electrical activity recorded by an EEG (ElectroEncephaloGram) in the waking state is

characterized by low voltage & high frequency. In deep non-REM sleep EEGs display high

voltage & low frequency, which is why deep non-REM sleep is also called Slow-Wave Sleep

(SWS). Although SWS corresponds to the lowest blood pressure, the least brain activity andthe deepest sleep, SWS is the stage in which sleepwalking occurs.
http://www.benbest.com/science/anatmind/anatmd10.html#serotoninhttp://www.benbest.com/science/anatmind/anatmd10.html#acetylcholinehttp://www.benbest.com/science/anatmind/anatmd10.html#acetylcholinehttp://www.benbest.com/science/anatmind/anatmd10.html#noradrenalinehttp://www.benbest.com/health/caffeine.html#contentshttp://www.lboro.ac.uk/departments/hu/groups/sleep/karger.htmhttp://faculty.washington.edu/chudler/sleep.htmlhttp://www.benbest.com/science/anatmind/anatmd10.html#serotoninhttp://www.benbest.com/science/anatmind/anatmd10.html#acetylcholinehttp://www.benbest.com/science/anatmind/anatmd10.html#noradrenalinehttp://www.benbest.com/health/caffeine.html#contentshttp://www.lboro.ac.uk/departments/hu/groups/sleep/karger.htmhttp://faculty.washington.edu/chudler/sleep.html


10/14

With long periods of wakefulness adenosine accumulates in neurons as a result of ATP

breakdown. Adenosine from inside the neurons is transported across cell membranes into the

extracellular space. The A1 receptors of the basal nucleus neurons are particularly sensitive to

the increased levels of adenosine, which increases potassium ion influx thereby

hyperpolarizing (inhibiting) those neurons. Adenosine also reduces the activity of GABA

neurons in the basal nucleus, thereby disinhibiting neurons in the preoptic/anteriorhypothalamus which promote Slow-Wave Sleep (SWS) [BEHAVIORAL BRAIN

RESEARCH 115:183-204 (2000)].

Caffeine promotes wakefulness by opposing all of these actions of adenosine blocking the

adenosine receptors. Additionally, the neurons in the raphe nucleus, locus coeruleus and

caudate nucleus are all very sensitive to the ability of caffeine to block the inhibitory

infulence of adenosine [BRAIN RESEARCH 858:71-77 (2000)]. For these reasons caffeine

is particularly effective in opposing the sleep-inducing actions of adenosine. Caffeine even

reduces "sleep" in fruit flies in a dose-dependent manner [SCIENCE; Shaw,PJ; 287:1834-

1837 (2000)].

Caffeine increases attention & vigilance and lessens feelings of weariness. Caffeine enhances

learning in maze tests in which animals are not rewarded, but makes no difference in tests

that include a food reward. Caffeine reduces the tendency to become bored by a repetitive

stimulus [BRAIN RESEARCH REVIEWS 17:139-170 (1992)]. Caffeine might therefore

seem well suited for those working at night, driving long hours or working with hazardous

equipment and may save lives.

(For more on the subject of sleep, see my essay The Nature of Sleep and its Impact on

Health.)


V. ADENOSINE, CAFFEINE AND ISCHEMIA/HYPOXIA

Ischemia, hypoxia and reperfusion can cause serious brain damage in stroke or cardiac arrest.

More than half of patients discharged from hospital after coronary-artery bypass grafting

show evidence of cognitive decline. Minimizing damage to ischemia & reperfusion is

critically important in organ transpantation & cryonics. (For more on this subject, see my

essay Ischemia and Reperfusion Injury in Cryonics.) There is much evidence that adenosine

can be neuroprotective in such cases.

Adenosine levels rise during ischemia/hypoxia and this effect is thought to counter the

detrimental effects by providing substrate for ATP synthesis and reducing excitotoxicity

through agonist actions of adenosine on A1 receptors. Selective antagonism of A2A receptors

has been suggested to reduce ischemia because A2A receptors actually mediate excitation in

the hippocampus (the area of the brain most vulnerable to ischemic/hypoxic

damage) [BRAIN RESEARCH 705:79-84 (1995)]. Additionally, blockage of A2A receptors

would be expected to cause enough vasoconstriction to reduce edema (although this could

worsen ischemia).

Nonetheless, the predominant effect of elevated adenosine is to protect against ischemic

damage, because A1 receptors predominate in number and have greater affinity for adenosinethan A2A. Not only does adenosine A1 stimulation reduce excitotoxicity by reducing
http://www.benbest.com/health/sleep.htmlhttp://www.benbest.com/health/sleep.htmlhttp://www.benbest.com/health/caffeine.html#contentshttp://www.benbest.com/cryonics/CryoFAQ.htmlhttp://www.benbest.com/cryonics/ischemia.htmlhttp://www.benbest.com/cryonics/ischemia.htmlhttp://www.benbest.com/health/sleep.htmlhttp://www.benbest.com/health/sleep.htmlhttp://www.benbest.com/health/caffeine.html#contentshttp://www.benbest.com/cryonics/CryoFAQ.htmlhttp://www.benbest.com/cryonics/ischemia.html


11/14

glutamaterelease, but lower metabolism due to hyperpolarization can reduce further ischemic

damage and assist in temperature reduction. Adenosine receptor drugs which selectively

stimulate A1 receptors and inhibit A2A receptors while being less readily metabolized than

adenosine would be superior to adenosine for protection from ischemia.

General blockage of all adenosine receptors by caffeine worsens ischemia/hypoxia, primarilythrough blocking the A1 receptors. Caffeine worsens reperfusion injury from neutrophil

accumulation in vascular beds an effect normally opposed by adenosine action on A2receptors.

Preconditioning with caffeine a few weeks prior to ischemia with caffeine discontinued

prior to the time of ischemia can reduce ischemic damage as a result of increased number

of A1 receptors due to habituation/tolerance. Taking advantage of caffeine in an actual

clinical/cryonics situation would be difficult because the timing of ischemic episodes &

clinical death cannot be predicted and the half-life of caffeine in a normal adult is roughly

5 or 6 hours.


VI. HEART DISEASE, CANCER AND CAFFEINE

Unlike many other foods or recreational drugs (like alcoholor nicotine), there is little

evidence implicating caffeine to cancerorcardiovascular disease although heart

disturbances can occur on high doses or in sensitive individuals. Administered acutely,

moderate doses of caffeine can increase blood pressure and decrease heart rate. For most

people, tolerance develops to these effects within a few days and there is no alteration in

cardiovascular effects for habitual caffeine users.

In a study of one hundred healthy males, 3 cups of coffee daily over 8 weeks led to a small

increase in both LDL & HDL cholesterol, which would not be expected to increase the risk of

coronary artery disease [JOURNAL OF THE AMERICAN MEDICAL ASSOCIATION

267(6):811-815 (1992)]. The cholesterol-raising factors have been identified as the lipids

cafestol & kahweol, which can be removed by paper filtration and are not present in instant

coffee [ANNUAL REVIEW OF NUTRITION 17:305-324 (1997)].

A study of nearly fifty thousand male health professionals showed no increase of

cardiovascular disease due to coffee-drinking [THE NEW ENGLAND JOURNAL OF

MEDICINE 323:1026-1032 (1990)] a result in agreement with the FraminghamStudy [ARCHIVES OF INTERNAL MEDICINE 149:1169-1172 (1989)]. Neither

caffeinated nor decaffeinated coffee are associated with an increased risk of myocardial

infarction [AMERICAN JOURNAL OF EPIDEMIOLOGY 149(2):162-167 (1999)].

However, coffee in excess of 8 cups per day may aggrevate cardiac arrhythmias [ANNALS

OF INTERNAL MEDICINE 114:147-150 (1991)] and raise plasma

homocysteine [AMERICAN JOURNAL OF CLINICAL NUTRITION 76:1244-1248

(2002)]. Adenosine is sometimes used in emergency medicine to treat supraventricular

arrhythmias [AMERICAN FAMILY PHYSICIAN 65(12):2479-2486 (2002)] and caffeine

may interfere with this treatment. Caffeine equivalent to two cups of coffee has been shown

to reduce heart blood flow 11% in an exercise test given to coronary heart disease

patients [PLOS ONE Namdar,M; 4(5):e5665 (2009)].
http://www.benbest.com/science/anatmind/anatmd10.html#glutamatehttp://www.benbest.com/science/anatmind/anatmd10.html#glutamatehttp://www.benbest.com/health/caffeine.html#contentshttp://www.benbest.com/health/alcohol.htmlhttp://www.benbest.com/health/alcohol.htmlhttp://www.benbest.com/health/cancer.htmlhttp://www.benbest.com/health/cardio2.htmlhttp://www.benbest.com/health/cardio2.htmlhttp://www.benbest.com/health/cardio2.htmlhttp://www.ncbi.nlm.nih.gov/pmc/articles/PMC1866181/http://www.benbest.com/science/anatmind/anatmd10.html#glutamatehttp://www.benbest.com/health/caffeine.html#contentshttp://www.benbest.com/health/alcohol.htmlhttp://www.benbest.com/health/cancer.htmlhttp://www.benbest.com/health/cardio2.htmlhttp://www.ncbi.nlm.nih.gov/pmc/articles/PMC1866181/


12/14

In the period between the 1950s and 1970s many believed that caffeine could be a serious

cause of cancer in humans because of studies in plants showing chromosome breaks,

inhibition of mitosis and formation of chromatin bridges after high-dose caffeine

treatment [MUTATION RESEARCH 26:53-71 (1974)]. A 1994 review, however, concluded

that caffeine at the doses experienced in coffee-drinking is not mutagenic in humans,

although heterocyclic amines from roasting and alkylating carbonyls in coffee are somewhatmutagenic [MUTATION RESEARCH 317:145-162 (1994)]. Nonetheless, more recent

evidence does show a capacity for caffeine to worsen the mutagenicity of ionizing radiation

and other carcinogenic agents through interference with cell cycle control [MUTATION

RESEARCH 532:85-102 (2003)].

Green tea is reputed to help prevent cancer due to its polyphenols.The polyphenol most

highly concentrated in coffee is chlorogenic acid (5-10%), but a coffee polyphenol present in

lesser concentrations (caffeic acid) is associated with anti-oxidant activity. Caffeine, like the

xanthine-derivative uric acid, is an antioxidant that can scavenge the hydroxyl radical which

can be produced from the hydrogen peroxide in coffee & tea undergoing aFenton reaction

with metal ions [FOOD AND CHEMICAL TOXICOLOGY 29(1):1-6 (1991)].

A review of studies on animals & humans found no conclusive evidence for any increased

incidence of cancer in any organ due to coffee [WORLD REVIEW OF NUTRITION AND

DIETETICS 79:185-221 (1996)]. In fact, a meta-analysis of epidemiological studies

concluded that persons consuming four or more cups of coffee per day have a 24% lower risk

of colon cancer than those who rarely or never drink coffee [AMERICAN JOURNAL OF

EPIDEMIOLOGY 147(11):1043-1052 (1998)]. Nonetheless, such an association might be

due to the higher socio-economic status of coffee-drinkers rather than to the coffee.


VII. OTHER EFFECTS OF CAFFEINE

Caffeine administered acutely increases diuresis (urination), but this effect is not seen for

habitual users who consume the equivalent of a few cups of coffee per day. Nor do such users

typically suffer much sleep disturbance especially when most caffeine is consumed in the

morning. Tolerance to these effects is believed to be due mainly to the adaptive increase

(upregulation) in number of adenosine receptors. Although tolerance is usually seen for

elevation of blood glucose by caffeine, there may be little tolerance of this effect for people

who are obese or who are suffering from maturity-onset diabetes.

Caffeine can significantly increase the secretion of gastric acid & pepsin. But coffee even

decaf has an even stronger effect. Apparently there is a non-caffeine component to coffee

which has a significant effect on gastric secretion.

Caffeine can increase plasma levels of free fatty acids, cortisol and epinephrine effects

thought to improve athletic performance. But effects on the brain may be more important for

improving endurance such as increased dopamine signalling in the basal ganglia and

reduced serotonin signalling (insofar as serotonin mediates fatigue). Elevated epinephrine &

free fatty acids due to caffeine may cause insulin resistance, but it remains undetermined

whether tolerance can develop to this effect [DIABETES CARE 25(2):304-369 & 399-400

(2002)]. Elevation of free fatty acids (which can be twice as high as normal) due to caffeine isnot simply due to elevation of epinephrine [JOURNAL OF APPLIED PHYSIOLOGY
http://www.benbest.com/health/cancer.html#chemicalshttp://www.benbest.com/health/cancer.html#cellcyclehttp://www.benbest.com/lifeext/aging.html#radicalhttp://www.benbest.com/lifeext/aging.html#radicalhttp://www.benbest.com/health/caffeine.html#contentshttp://www.benbest.com/health/cancer.html#chemicalshttp://www.benbest.com/health/cancer.html#cellcyclehttp://www.benbest.com/lifeext/aging.html#radicalhttp://www.benbest.com/health/caffeine.html#contents


13/14

80(3):999-1005 (1996)]. Obese women increase thermogenesis in response to caffeine to a

lesser extent than do lean women [AMERICAN JOURNAL OF PHYSIOLOGY

269(4 Pt 1):E671-E678 (1995)].

Caffeine regularly increases energy metabolism throughout the brain while decreasing

cerebral blood flow and there is no tolerance for these effects. Vasoconstriction due to250 milligrams of caffeine can decrease central blood flow by 20-30%, which is why caffeine

has been used to treat migraine headache. Because blood glucose is usually more than ample

for cerebral metabolism the combination of increased metabolism & decreased blood flow

would be more likely to induce hypoxia than ischemia. But if caffeine increases oxygen

intake by bronchodilation or increases sensitivity to carbon dioxide in the medulla, then there

may be compensation. (Both hypoxia and caffeine elevate plasma adenosine.)

Green tea three times per day can increase total basal metabolism by 4%, but this effect is

more due to epigallocatechin gallate than caffeine [AMERICAN JOURNAL OF CLINICAL

NUTRITION; Dullo,AG; 70;1040-1045 (1999)].

Caffeine can increase both the prevalence and severity of PreMenstrual Syndrome (PMS).

Among women with severe PMS a single daily cup of caffeine beverage increased the chance

of PMS by one third, whereas 8-10 daily cups increased the prevalence seven

times [AMERICAN JOURNAL OF PUBLIC HEALTH; Rossignol,AM; 80(9):1106-1110

(1990)].

The consumption of fewer than four cups of coffee daily during pregnancy is not deemed to

endanger the child [FOOD AND CHEMICAL TOXICOLOGY 40:1271-1310 (2002)]. For a

60 kilogram (132 pound) pregnant woman, an increased risk of spontaneous abortion is only

seen for coffee consumption in excess of 6 cups per day (equivalent to 12 cups of tea) [NEW

ENGLAND JOURNAL OF MEDICINE; Klebanoff,MA; 341(22):1639-1644 (1999)].

There can be considerable individual variation in the response to caffeine. People with high

anxiety tend to consume less caffeine. Those who report anxiety due to caffeine usually do

not report heightened-alertness, and vice-versa. People who normally consume large amounts

of caffeine report more positive mood changes compared to those who consume the caffeine

only as part of an experiment. Extroverts show performance improvement with caffeine when

doses are large, whereas introverts show performance impairments on large doses.

Caffeine can offset the effects of alcohol when the levels of caffeine are high and the levels

of alchohol are low. The reversal is best for the sleep-inducing effects of alcohol, but co-ordination & performance may not improve leaving a "wide-awake drunk".

Without caffeine, habitual users experience withdrawal symptoms that typically peak the

second day and are gone after the third day. Throbbing headache is the most common

complaint followed by fatigue or sleepiness and anxiety or irritability. Poorly-planned studies

purportedly demonstrating improved performance with caffeine have included habitual

coffee-drinkers experiencing withdrawal symptoms in the placebo group. Some researchers

provide evidence for the withdrawal reversal hypothesis which claims that the only benefits

of caffeine on mood, alertness, and mental performance are the reversal of withdrawal

symptoms on habitual users [PSYCHOPHARMACOLOGY 167:54-62 (2003)]. This result

seems inconsistent with the fact that caffeine increases brain metabolism, and that there islittle tolerance or adaptation to this effect (despite the increase in adenosine receptors).
http://www.benbest.com/nutrceut/phytochemicals.html#catechinhttp://www.ajcn.org/cgi/content/full/72/5/1142http://www.ajcn.org/cgi/content/full/72/5/1142http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Retrieve&dopt=AbstractPlus&list_uids=2382749http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Retrieve&dopt=AbstractPlus&list_uids=2382749http://content.nejm.org/cgi/content/full/341/22/1639http://content.nejm.org/cgi/content/full/341/22/1639http://www.benbest.com/nutrceut/phytochemicals.html#catechinhttp://www.ajcn.org/cgi/content/full/72/5/1142http://www.ajcn.org/cgi/content/full/72/5/1142http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Retrieve&dopt=AbstractPlus&list_uids=2382749http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Retrieve&dopt=AbstractPlus&list_uids=2382749http://content.nejm.org/cgi/content/full/341/22/1639http://content.nejm.org/cgi/content/full/341/22/1639


14/14

Heritablity of heavy caffeine use has been estimated at 77% independent of family

environment [THE AMERICAN JOURNAL OF PSYCHIATRY; Kendler,KS; 156(2):223-

228 (1999)].

(A very thorough review of the effects of caffeine on the brain can be found in

[PHAMACOLOGICAL REVIEWS; 51(1):83-133 (1999)].)
http://ajp.psychiatryonline.org/cgi/content/full/156/2/223http://ajp.psychiatryonline.org/cgi/content/full/156/2/223http://pharmrev.aspetjournals.org/cgi/content/abstract/51/1/83http://ajp.psychiatryonline.org/cgi/content/full/156/2/223http://ajp.psychiatryonline.org/cgi/content/full/156/2/223http://pharmrev.aspetjournals.org/cgi/content/abstract/51/1/83

is caffeine a health hazard

Documents