How Caffeine Affects People
The drugs that are responsible for the most deaths are the drugs that are legal for adult
use in the US, not those that people typically think of as the most “dangerous.” What
makes a drug legal or illegal has very little to do with the drug itself. Drugs rarely, if
ever, become illegal because they are more deadly, more dangerous, or more addictive
than other substances. Surprisingly, the drug that has the highest addiction liability- how
likely a user is to become addicted to it – is caffeine. Coffee, tea, cacao, and kola nuts
have all been gathered and cultivated for centuries to make foods, tonics, and beverages
meant to boost energy levels and clarify thought—all as the result of the caffeine in these
substances. Caffeine remains the most commonly used addictive drug in the world.
Caffeine Consumption
Caffeine is the most widely used psychoactive drug in the world. More than 80% of
Americans over the age of 12 consume caffeine on a regular basis. The average
consumption is about 200 mg/day, with the most popular sources being soda, coffee, tea
and energy drinks. Although chocolate contains stimulant chemicals, it has far less
caffeine than is commonly believed.
Physical Effects of Caffeine Consumption
Caffeine can provoke some unique physical effects, including an increase in heart rate,
blood pressure, mental alertness, vasoconstriction, restlessness, and tremors. Caffeine can
increase the production of gastric acid, which may pose a problem for individuals with
chronic heartburn or acid reflux, and some doctors recommend patients with these
problems avoid caffeine consumption.
Caffeine causes vasodilation of blood vessels in the periphery, but vasoconstriction of
cerebral blood vessels. This is one reason why many headache formulations of over-thecounter pain treatments include caffeine. Although some headaches, including migraines,
are often believed to be caused by changes in blood vessel dilation, this seems not to be
the case. Caffeine’s success in treating many headaches may be due to some headaches
being caused by caffeine withdrawal. Finally, as most regular caffeine users know all too
well, caffeine has a diuretic effect and increases urine output. For this reason, caffeine
should be avoided during exercise and in very hot weather because of the potential for
dehydration.
Neurons
Image from http://webspace.ship.edu/cgboer/theneuron.html
Brain is made up of millions of nerve cells called neurons. The electrical signals in
neurons are what processes information in the brain. The passage of these electrical
signals between neurons is how areas in the brain communicate with each other and with
other parts/systems of the body. Neurons have a large number of extensions called
dendrites. They often look likes branches or spikes extending out from the cell body. It
is primarily the surfaces of the dendrites that receive chemical messages from other
neurons.
One extension is different from all the others, and is called the axon. The purpose of the
axon is to transmit an electro-chemical signal to other neurons, sometimes over a
considerable distance. In the neurons that make up the nerves running from the spinal
cord to the toes.
Neurotransmitters
The electrical signals from inside neurons are passed on
from one neuron to another by chemical messengers
called neurotransmitters. By using a relatively small
number of these chemicals, the brain is able to produce
the billions and billions of thoughts, emotions, reflexes,
movements, sensory interpretations, and other functions
that take place in the body every moment of every day.
The reason so few chemicals can produce so many
results is that these chemicals are released from the
neurons in a coordinated way with one another, and
each one binds to a select group of receptors. By
binding to these receptors on neurons in different areas
of the brain, the same neurotransmitter can elicit a
multitude of effects.
Image from http://www.integrativepsychiatry.net/neurotransmitter.html
Caffeine Mechanism
In the left image, left is caffeine, and right is
adenosine. Note the red arrow points to a
module in adenosine, which is very similar to
caffeine.
Image from http://bioidenticalmds.blogspot.com/2013/06/making-coffee-outof-this-world-by.html
Caffeine does not directly affect dopamine levels in the brain. Caffeine works by
blocking adenosine receptors.
Image from http://healthyprotocols.com/2_caffeine.htm
Adenosine is a neurotransmitter that governs one of the many feedback mechanisms in
the brain. Throughout the day, levels of adenosine build up in the brain. When they reach
a particular set point, they trigger activation of the ventral lateral preoptic area (VLPA) in
the brain. The VLPA begins the process of decreasing activity of other energy activating
neurotransmitters. Activation of the VLPA is what makes people begin to feel fatigued
and drowsy. This lowered activity is in preparation for sleep.
By blocking the receptors that adenosine normally binds to, caffeine prevents the
activation of the VLPA. If the VLPA is not triggered, people will not feel as fatigued and
sleepy. This is why caffeine reduces fatigue more than it increases energy. This is also
why caffeine may seem more effective at reducing fatigue later in the day. Levels of
adenosine are typically low in the morning. This is also why caffeine users may feel as
though they “crash” when the effects of caffeine wear off.
While people are awake and alert, adenosine continues to accumulate. Once caffeine is
no longer blocking those adenosine receptors, there is enough adenosine available to bind
to all active receptors, making user feel suddenly very fatigued.
Long Term Effects of Caffeine Consumption
There is no evidence of long term organ damage occurring in response to caffeine use.
Many doctors have been concerned with caffeine’s effects on the cardiovascular system
and its potential effects on cardiovascular disease. It is true that caffeine will raise blood
pressure and heart rate while the caffeine is in the bloodstream. However, these effects
appear to be transient and dissipate when the caffeine is metabolized. There is no
evidence that caffeine alone increases the risk of cardiovascular disease, but people who
do have a history of cardiovascular disease may want to limit their caffeine intake.
Regular caffeine use will quickly lead to tolerance, so that in a short period of time users
will stop noticing some of the immediate side effects of caffeine (jitters, tremors, and
agitation). With heavy long term use, some users may find that they develop a tolerance
to caffeine’s more stimulating effects. Occasionally someone builds up enough tolerance
that caffeine ingested late in the day does not prevent them from becoming drowsy or
sleepy at night.
One of the more controversial aspects of caffeine use is its effects on pregnancy. Despite
numerous studies, there is very little scientific evidence that suggests caffeine has any
negative impact on pregnancy at low to moderate amounts. A few studies have suggested
that women who ingest more than 300 mg of caffeine per day are at an increased risk of
miscarriage. It should be noted that while the evidence of any harm of caffeine ingestion
during prenancy is limited or mixed, there is no harm in not consuming caffeine.