All About Caffeine

Finals are coming up soon! How much do you know about how all that coffee you’re drinking is affecting your body? 

What is caffeine?

Caffeine is a bitter white crystalline alkaloid that acts as stimulant and a mild diuretic. It is found in the beans, leaves, and fruits of more than 60 plants. In these tissues it serves as a pesticide, killing or paralyzing insects that feed on them.⁽²⁾

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Where does it come from?

Major sources of caffeine for human consumption come from coffee, tea, and cocoa. Guarana, kola nuts, and yerba mate are also cultivated for use as sources of caffeine in energy drinks and snacks.⁽²⁾

Who consumes caffeine and how much do they have?

Caffeine is the most widely consumed stimulant in the world. Adults in the US consume an average of about 300 mg of caffeine a day, and 80% of adults in the US consume caffeine in the form of coffee or tea on a daily basis.⁽²⁾ 97% of the total caffeine consumed comes from beverages, and coffee accounts for the majority of these beverages.⁽⁴⁾ An average adult in the US consumes about 3.3 9oz cups of coffee per day.⁽¹⁾ 

What does it do?

Average doses (85-250 mg, the equivalent of 1-3 cups of coffee) can result in feelings of alertness, decreased fatigue, and eased flow of thought.  High doses (250-500 mg) can result in restlessness, nervousness, insomnia, and tremors.⁽³⁾ 

At very high doses, caffeine can cause seizures and cardiovascular instability.  Overdosing on caffeine is difficult because a fatal dose in adults, 10g, is over 20x what most people consume in a day.⁽³⁾  With that in mind, the FDA still recommends that the average daily intake of caffeine for adults should be less than 500 mg per day.⁽²⁾

How quickly does it act, and for how long?

After being ingested, caffeine is rapidly absorbed. It is detectable in the blood after only 5 minutes and reaches its peak levels after 30-60 minutes.  The half life varies from person to person, but generally is about 5-8 hours, meaning that in 5-8 hours only half the caffeine you ingested will remain in your system. If you are a tobacco smoker however, it is cleared from your body more quickly.⁽³⁾

How does it work?

The nucleoside adenosine plays many roles in your body, one of which is to promote sleep and suppress wakefulness.⁽³⁾ Caffeine acts as an adenosine antagonist, binding to adenosine receptors and preventing adenosine from binding to the receptor.⁽⁵⁾ This results in the opposite action of adenosine, causing your blood vessels to dilate and your central nervous system to be stimulated.⁽³⁾

Caffeine also induces the release of signaling molecules such as norepinephrine and epinephrine, increasing heart rate and blood vessel dilation, as well as increasing oxygen absorbance at the lungs.  It can also induce a number of metabolic changes, increasing blood sugar and blood filtration at the kidney. It also increases the amount of acid in your stomach and increases the movement of food through your digestive tract.⁽³⁾

How can this help you as a student?

Doses of caffeine over 100mg reliably produce beneficial effects for reaction time, sustained attention tasks, alertness, mood, and wakefulness.  Additionally, glucose has synergistic effects with caffeine, benefiting sustained attention and verbal memory.⁽⁶⁾

Chronic low doses of caffeine have been shown to prevent learning and memory impairment in animal models of Alzheimer’s disease.⁽⁵⁾ However, this has not yet been reported in humans. 

If you want to know more:

Search SciFinder, PubMed, or Web of Science for information about caffeine; you may want to start by filtering for reviews. If you want a more general overview, try a subject search in OBIS on caffeine.  If you want assistance, come to the science library reference desk and we can help you search.  Here are a few recommended titles:

• The world of caffeine : the science and culture of the world's most popular drug / Bennett Alan Weinberg, Bonnie K. Bealer
• Coffee, tea, chocolate, and the brain / edited by Astrid Nehlig
• Buzz : the science and lore of alcohol and caffeine / Stephen Braun
• Caffeine and health research / Kenneth P. Chambers, editor

Sources:

1. National Coffee Drinking Trends 2010, National Coffee Association
2. Food and Drug Administration 2010 Caffeine Report
3. http://emedicine.medscape.com/article/821863-overview#a0101
4. Laszlo SP. Caffeine Intake By the U.S. Population. US Food and Drug Administration.
5. J Alzheimers Dis. 2010;20 Suppl 1:S3-15. doi: 10.3233/JAD-2010-1379. Caffeine and adenosine. Ribeiro JA(1), Sebastião AM.
6. Hum Psychopharmacol. 2010 Jun-Jul;25(4):310-7. doi: 10.1002/hup.1115. Effects of caffeine and glucose, alone and combined, on cognitive performance. Adan A(1), Serra-Grabulosa JM.

Contributed by: James Medina, Science Library Student Reference Assistant