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Biology 202
2000 Third Web Report
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Effects of Caffeine on the Body

Anjali Patel

As finals week rolls around more and more students look to caffeine to help them make it through their exams and final papers such as this one. Some drink coffee or sodas, while others take caffeine pills like No Doze. Here at Bryn Mawr students are given "Study Breaker" packages for free that come with samples of shampoo, razors, and packets of Vivarin. Caffeine can be found in all types of items such as Midol, tea, and chocolate bars. You can even buy caffeinated water! Caffeine is probably the most popular drug in the world. In the United States alone 80% of the adult population drink coffee or tea on a regular basis. (1) With exams, projects, and papers due in less than a week I know I have been taking in mass quantities of caffeine via Coca-Cola. Practically everyone I know is getting some type of caffeine intake. I started becoming curious as to how caffeine stimulates my nervous system and if it has any adverse effects especially in the female body. And thus I stumbled upon my topic for the Final Neurobiology Paper.

Caffeine, medically known as trimethylxanthine (C8H10N4O2), is a bitter tasting white crystalline powder or as silky needles when found in its purest form. (2) The some of the positive effects of caffeine are improvements in motor performance, sensory activity, alterness, and a decrease in fatigue. Caffeine, in the right amount can cause insomnia, irritability, headaches, nervousness, and dizziness. It can also dehydrate the individual. (1) The reason students drink coffee and soda is because caffeine increases alterness and the amount of time it takes to fall asleep, making it the prefect remedy for "pulling an all nighter". The reason caffeine works so well as a stimulant for the nervous system is because it enters the blood stream 15 minutes after it has been consumed and it takes the body 6 hours to eliminate half of the caffeine. Like everything if taken in massive doses caffeine can be lethal; A lethal dose is calculated to be approximately 10 grams, in another words you would have to drink over 80 cups of coffee in succession for caffeine to kill you. (1)

There is a chart to show the amount of caffeine found in particular items:



Content (mg)

Coffee 150 ml


Coffee, decaffeinated 150 ml


Tea 150 ml


Chocolate 225 ml


Jolt Cola 12 oz


Mountain Dew 12 oz


Surge 12 oz


Coca Cola 12 oz


Dr. Pepper 12 oz


Pepsi Cola 12 oz


Ben/Jerry No Fat Coffee
Fudge Frozen Yogurt
1 cup


Chocolate Bar 50 g


Vivarin 1 tablet


No Doze 1 tablet


Midol 1 tablet



Now the important question to answer is how does caffeine effect the body? To fully understand how caffeine effects the body at the cellular level we must take a trip back to Intro Biology. Here I would like to give a brief over view of cell communication. A series of steps in which a signal on the cell's surface is converted into a cellular response is referred to as a signal-transduction pathway. Within most pathways a series of protein kinases add phosphate groups to the next one in line and thereby activating it. Cyclic adenosine monophosphate (cAMP) and calcium ions, both are second messengers, diffuse through the cytosol to help transmit signals throughout the cell. Epinephrine binds to a specific receptor protein and thus activates the enzyme adenylyl cyclase. This enzyme then converts ATP to cAMP. This leads to a chain of events and in the end glucose is produced. (3)

Once caffeine enters the blood stream via absorption in the stomach and small intestine, it inhibits the action of the adenylyl cyclase enzyme. How does it do this? Caffeine is structurally similar to the chemical adenosine. (4)The caffeine molecules compete with adenosine for binding sites on the cell surface. Thus the enzymes are not activated to break down cAMP; meaning that ATP is not converted to glucose. With an increase of cAMP levels the heart prompts norepinephrine (noradrenalin) and the neurotransmitter epinephrine to increase the rate and the force of the muscle contractions. The sympathetic nerves located near the pacemaker tissue in the heart release norepinephrine. The pituitary gland releases hormones that activate the adrenal glands to produce epinephrine (adrenaline). This chain of events produces the "fight or flight" behavior in the body. This behavior increases the rate and force of the heartbeat and thereby providing the brain and other tissues with more oxygen. (5)

The effects of adrenaline on the body are:

Another effect of caffeine is that it increases the level of dopamine. This neurotransmitter affects the brain processes that control the ability to experience pleasure and pain. It is believed that the increased levels of dopamine contribute to the addiction to caffeine. (2)

It is easy to see how people can get addicted to caffeine. You have a long day ahead of you so you drink some coffee. This initiates the "fight or flight" behavior in your body, giving you an extra boost of energy from adrenaline. The release of dopamine makes you feel good. So what happens when the caffeine wears off but the day isn't over yet? You drink some more coffee. Once someone gets into the cycle its hard to break away from it. A person can go through withdrawal symptoms when they try breaking away from the cycle. Some of these withdrawal symptoms include headaches, drowsiness, lethargy, yawning, irritability, nervousness, depression, and nausea. (6)

What got me curious about how caffeine effects women was when I looked at the back of a Midol packet. I was surprised to see that the recommended dosage contains about as much caffeine as a cup of coffee; I had always been told to stay away from caffeine when on my period. Perhaps there is caffeine in the tablets so it can diffuse into the bloodstream quickly and provide relief of the symptoms for a longer duration of time. I had trouble finding any concrete evidence that proves that caffeine has adverse affects in women. Some web sites provided information to show that caffeine does not effect miscarriage, birth defects, fertility, and calcium loss. Then there were web sites that stated just the opposite.

The web sites did agree on one thing: the effect of caffeine on the body all depends on the person and their life style. According to the American Medical Association, "Moderate tea or coffee drinkers probably need have no concern for their health relative to their caffeine consumption provided other lifestyle habits (diet, alcohol consumption) are moderate, as well." (7) Since the effect of caffeine varies from person to person researches have had difficulty in producing conclusive results as to if and how caffeine affects women.

Even though the FDA does not believe that caffeine has an adverse affect in the reproduction of humans, they recommend pregnant women to consume caffeine in moderation. (7)Caffeine can cross the placenta and enter the fetus. Thus the caffeine could affect foetal heart rate and breathing. (8)Studies have been done to discover a relationship between caffeine and premature births and low birth weight; it was concluded that a moderate intake of caffeine would not have an adverse effect in those areas. (7)A study done in 1988 indicated that an intake of 120-300 mg of caffeine daily could decrease female fertility. This study, however, was found to be inconclusive when other variables that effect life style were factored in. (9)Caffeine can be found in breast milk. According to a study done by Nehligh and Derby in 1994, "The amount of caffeine in five or fewer 5-ounce cups of coffee per day (less than 750 ml) will not cause a problem for most breastfeeding mothers and babies... If a breastfeeding mother consumes [more than 750 ml/day], caffeine could begin accumulating in her baby's system, causing the symptoms of caffeine stimulation." (10)

Caffeine does not decrease the amount of calcium found in the body. Nevertheless, studies have found an increased risk of bone fractures in women who intake caffeine but it is not certain why they might be connected. Caffeine has not been found to be a major factor for osteoporosis. However, phosphorus, an ingredient of carbonated sodas, has been found to be a possible risk factor for osteoporosis. (11)

As I sit here drinking a glass of Coca-Cola I know exactly what it is doing to my body. Soon my body will be in the "fight or flight" behavioral mode and I will be ready for another day of studying for my final exams. Many students use caffeine as a quick fix to get through the day without entirely realizing how it effects their body. All they know is that it keeps them awake and going and that is all that matters. If people are not careful about how much caffeine they take in they can become extremely dehydrated and have a high blood pressure. As with any drug, it is important not to become too reliant and addicted to it.

WWW and Other Sources

1)Effects of Caffeine on the Nervous System, on University of Washington web site

2)How Caffeine Works by Marshall Brain, How Stuff Works web site

3)Introduction to Biology text book

4)Behind the Buzz, on web site

5)How does caffeine affect the body? , Scientific American article

6) Caffeine, SC prevents alcohol, tobacco and other drug abuse

7)Everything you need to know about Caffeine, an article on women's health and caffeine

8) Caffeine During Pregnancy , an article on women's health and caffeine

9) Caffeine and Women's Health , an article on women's health and caffeine

10)"How long does it take alcohol and caffeine to wind up in my milk?" , Question & Answer Forum

11)What's the Link Between Caffeine and Calcium?, Ask the Doctors web site

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