Caffeine Induces Anxiety in College Students

Caffeine Induces Anxiety in College Students

What Is Caffeine?

Caffeine, also known as methyl xanthine, 3,7-dihydro-1,3,7-trimethyl-1H-purine-2,6-dione, theine, theobrine, and 1,3,7-trimethylxanthine (Newton, 2014), is an alkaloid, crystal white in color, and a powdery substance. It is bitter to the tongue and has powerful antioxidant traits (Alpert,2012). Being a part of the alkaloid family, caffeine is a chemical compound identifiable in many organisms. Part of caffeine’s chemical compound make-up is nitrogen and exists in a complex multi-ring form (Thomasson, 2014). The complete chemical structure of caffeine is C8H10N4O2 H2O; these elements are Carbon, Hydrogen, Nitrogen, Oxygen, and the addition of the compound water (Newton, 2014).

Caffeine is also a methylxanthine, which is a phytochemical created from xanthine and is retrieved from plant supporting metabolism (Monteiro, Alves, Oliveira, & Silva, 2016).

Caffeine is considered an organic stimulant; it rouses the central nervous system and intensifies cyclic adenosine monophosphate (AMP) activity. Caffeine can travel through several molecular passages in the body, which can induce numerous biological and physiological reactions (Tolley, 2014). As caffeine is mostly ingested orally, it begins to process absorption through the small intestine and metabolized through the liver. Then, caffeine travels to all body tissues, passes through the blood-brain barrier, blood-placenta barrier, and the blood-testis barrier. However, the method of how caffeine travels, breaks down, and exits the body differ across individuals, leading to variations in physiological reactions. Due to these differences, caffeine can have effects on the body that last from a minimum of 2 hours to a maximum of 12 hours.

One way caffeine travels through the body and takes effect is by obstructing adenosine receptors (Cappelletti, Daria, Sani, & Aromatario, 2015). Adenosine receptors play roles in many bodily functions such as sleep, regulation of pain, circulation, immune function, and cardiac rhythm (Welch, 2015). Because caffeine blocks adenosine receptors, a surge of hormones is released, including dopamine, norepinephrine, and serotonin (Monteiro et al., 2016). When adenosine receptors are blocked, alertness, wakefulness, and focus are temporarily increased (Alpert,2012).

History and Forms of Caffeine Popularly Consumed
Caffeine can be found in over sixty plants around the world, and it is theorized that it acts as a protector to these plants. Caffeine is not needed for any plant to survive, yet it is found in many. The traces of caffeine found in plants are toxic to many insects and animals, primarily herbivores (Cappelletti et al., 2015). Of the sixty-plus plants that contain caffeine, the most popular species are Paullinia, Coffea, Theobroma, Ilex, and Camellia (Russo, & Romano, 2012).

Humans began to realize the benefits of caffeine in the Stone Age era. They would chew or consume certain bark, berries, or plants that contained caffeine. These specific plants would reduce tiredness and increase alertness to those who consumed them. Soaking leaves containing caffeine in hot water was discovered in the 10th century B.C.E in China. The making of other beverages with caffeine, like spicy hot chocolate, was discovered by the Olmec people in the Gulf of Mexico during the same century. People in 3rd century C.E Ethiopia collected coffee beans from ashes and crushed them in water. Again in Ethiopia, the method of wrapping beans containing caffeine in lard was discovered in the 9th century C.E. The extraction of caffeine by decaffeination was discovered in the 20th century and started the use of caffeine in many other beverages and the medical field (Alpert, 2012).

Caffeine can also be created synthetically by combining malonic acid and dimethyl carbamide, or by methylating theobromine. Synthetic caffeine, especially in pure form, can be dangerous (Russo, & Romano, 2012). Presently, the most popular consumed items containing caffeine are coffee, tea, chocolate, soft drinks, and energy drinks. These items all come from the aforementioned plants.

After water, coffee is the most consumed beverage globally. The caffeine content in coffee varies depending on which plant the coffee bean comes from, how it’s processed, and how it’s brewed. Robusta bean plants have a 2% or more caffeine concentration, while Arabica bean plants only have a 1% concentration (Massey, 2016). Coffee beans come from a tree that produces flowers. These flowers hold a fruit that contains the coffee bean. The flowers that contain the fruit are usually white, but the fruit can vary in color—yellow, red, orange, or pink. After retrieval, three layers of the fruit must be removed to get the bean (Steiman, Morris, & Thurston 2013). Although the fruit has other layers, none of them contain caffeine, resulting in large amounts of waste (Massey, 2016). The bean is then dried out to start processing (Steiman, Morris, & Thurston 2013).

The roasting process extracts more caffeine but in a less concentrated form. The espresso process extracts less caffeine, but in a higher concentration, so it is more potent. A Turkish method of brewing involves mixing ground coffee and hot water together, but leaving the residual, ground coffee as part of the final serving. Since the ground coffee is mixed with water for a longer period, it does dilute the caffeine concentration; however, because the coffee residue remains, it adds some concentration back.

Another example of brewing would be with an automatic coffee machine.
In the automatic method, water is slowly dispensed through a filter holding coffee grounds and collected underneath the filter. This process is fast and does not allow the water to contact the coffee grounds for a long period, so the caffeine content by the automatic machine is very diluted (Goodman, 2012).

Tea is the third most consumed beverage worldwide, after water and coffee. However, it is the second cheapest beverage to purchase after water. All tea leaves come from the plant Camellia sinensis (Tolley, 2014). The caffeine released in tea depends on the size of the leaf and fermentation. Smaller leaves, like those found in tea bags, release more caffeine than whole tea leaves. The entire Camellia plant contains caffeine, but only the leaves are used for the creation of tea. Although tea has a higher concentration of caffeine than coffee, it is served in large quantities of water, so the caffeine becomes diluted (Khan, & Mukhtar, 2013).

There are three popular fermentation processes to create black, oolong, and green tea leaves. Black tea leaves are created by first fermenting them by oxidizing them in air for several hours, then smoked or steamed. Oolong tea leaves are created through a half fermentation process, but the process is shorter than that of black tea. Green tea leaves are not fermented at all. The leaves are picked at an earlier stage and prevented from being able to oxidize, they go directly into the steaming, smoking, or panning process. Black tea has the highest caffeine content, followed by oolong, and green tea has the least (Khan, & Mukhtar, 2013).

Most energy drinks and soft drinks are made with synthetic caffeine and a plant called Guarana that also contains caffeine (Woolf, & Brown, 2008). Guarana is a vine plant with berry-shaped fruit containing seeds originating in South America. According to history, it was first discovered in Brazil and then spread to other parts of South America. The Guarana seeds have the highest caffeine concentration, surpassing coffee, tea, and the other sixty plants with concentrations ranging from 2% to 7.5%. The process of obtaining Guarana seeds is more complex than coffee. When the fruit is ripe, the first layer is opened to expose the seed. The skin surrounding the seed must soften for a few days, be peeled by hand, roasted on a large griddle, crushed by a mortar, mixed with water, shaped into cylinders, dried in the sun, and then smoked for a few weeks. Guarana can also be left in the powder form from being crushed by the mortar, but it loses its flavor and potency faster than the cylinder form (Smith, & Atroch, 2010).

The FDA has regulations on how much caffeine is allowed in soda, which is 65 mg per 12 oz. Energy drinks are not considered soda or soft drinks and do not have to follow those guidelines (Rath, 2012). Guarana is considered a natural ingredient, and the caffeine content from this plant that is incorporated into drinks is not required nor often reported to consumers (Woolf, & Brown, 2008). For example, Zhang et al. (2012) conducted a study on the caffeine content of 38 different beverages, including soft drinks and energy drinks. The results found that out of the 38 beverages, four had mislabeled caffeine content listed (Zhang, et al., 2012).
Synthetic caffeine is created in laboratories and mass-produced exclusively in factories. There are several methods for creating synthetic caffeine, such as the methylation of theobromine and combining carbamide and malonic acid (Russo, Romano, 2012). Additional methods include using raw urea and synthesizing it or exposing urea to strong chemicals like ethyl acetate, carbon dioxide, and methylated chloride. Synthetic caffeine is more potent than any plant-based caffeine, including Guarana.

Because synthetic caffeine is stronger than plant-based caffeine, it passes through the small intestine and metabolizes faster. This rapid metabolism results in quick energy increases and a faster caffeine crash. Unlike plant-based caffeine, synthetic caffeine doesn’t contain any vitamins or nutritional value, leading to a higher likelihood of adverse effects when consumed (Ettinger, 2011). Energy drink consumption, unlike coffee, tea, and soda, became prominent when Red Bull was released in 1997 (Malinauskas, Aeby, Overton, Carpenter-Aeby, Barbara-Heidal 2012).

College Students and Consumption of Caffeine

Over the past decade, companies selling caffeine-containing products have increased their advertising efforts towards young adults and adolescents. This has resulted in a significant rise in caffeine consumption among these populations (Paulus, et al., 2015). In the U.S in 2007, 37% of 18-24-year-olds reported consuming coffee, according to the National Coffee Association (McIlvain, Noland, & Bickel, 2011). For a healthy adult, the recommended caffeine limit is 400 mg per day (Zhang, et al., 2012). However, the National Library of Medicine suggests a lower daily dose of 200-300 mg (Paulus, et al., 2015).

Examples of caffeine content in popular coffee beverages include: Starbucks Grande 16oz coffee – 372mg, Starbucks Tall 12oz Caffe Latte – 58mg, Starbucks Grande 16oz Latte Macchiato – 225mg, Dunkin Donuts 24oz Iced Coffee – 297mg, Dunkin Donuts 14oz Brewed Coffee – 210mg, Peet’s 16oz Brewed Coffee – 267mg, Peet’s 16oz Caffe Latte – 140mg, Folgers 8oz Coffee – 112mg, and McDonald’s 22oz Iced Coffee – 200mg. Caffeine content in popular tea beverages include 8oz Black Tea – 42mg, 8oz Green Tea – 25mg, 8oz Oolong – 37mg, Turkey Hill 16.2oz Iced Tea – 110mg, Teavana 8oz Tea – 41mg, and Chai 8oz Tea – 50mg. The caffeine content of popular energy drinks includes Red Bull 8.4oz – 80mg, Monster Energy Drink 16oz – 160mg, Amp Energy Drink 16oz – 142mg, Rockstar Energy Drink 16oz – 160mg, and NOS Energy Drink 16 oz -160mg. Besides, the caffeine content of popular sodas includes Coca-Cola 12oz – 34mg, Pepsi Cola 12oz – 38mg, Sprite 12oz – 0mg, Diet Coke 12oz – 46mg, and Dr. Pepper 12oz – 41mg (Caffeine Informer, n.d.).
All beverages above meet the criteria of being below the recommended intake of 200-400mg per day. However, college students usually consume more than one of these beverages or a combination of these beverages. In a study done by McIlvain, Noland, & Bickel (2011), 300 freshman college students from Marshall University in West Virginia were evaluated for caffeine consumption, thoughts, and experiences with caffeine. Caffeine consumption in this study was calculated by the creation of an expansive list of caffeinated beverages and serving size. Students were asked which and how much of each drink they consumed in a day. The results showed that the average intake of caffeine amongst the students was 849.86 mg per day (McIlvain, Noland, & Bickel, 2011).

Another study done by Kuler (2010) in Turkey at the Kocaeli Vocational School of Health Services surveyed 156 students to discover the students’ daily caffeine intake and their experience with caffeine. A list of Turkish caffeinated items was distributed to students to report items they had consumed daily. The study results showed the average daily intake of students ranged from 0 mg to 500 mg with 51 percent of student’s intakes ranging from 0 mg to 200 mg and 49 percent of students ranging from 200 mg to 400+ mg (Kuler, 2010).

A study done in Pakistan at Dow University of Health Science by Khan, Nisar, Naqvi, and Nawab (2017) was a cross-sectional study carried out with 400 medical students over the course of 5 months. Although this study did not collect exact caffeine intake, it did cover how many students use caffeine and their beliefs. The results showed that only 6% (24 students) did not use caffeine in any form (Khan, Nisar, Naqvi, & Nawab, 2017).

Another cross-sectional study done in Dubai at Zayed University by M. Al Ghali, Al Shaibi, Al Majed, & Haroun (2017) studied 175 students’ caffeine intakes through self-report. 86% of students consumed caffeine. The average daily caffeine intake in this study was 249.7 ± 235.9 mg (M. Al Ghali, et al., 2017).

A study done by Malinauskas, Aeby, Overton, Carpenter-Aeby, Barbara-Heidal (2012) surveyed 496 students from different universities over the Central Atlantic region of the U.S. The study assessed energy drink consumption, intake on a given month, and reasoning for using energy drinks. The study showed that 253 students, 51%, reported consuming at least one energy drink per month (Malinauskas, Aeby, Overton, Carpenter-Aeby, Barbara-Heidal, 2012).

The last study was done in Benin, Africa, to get a report on how many students were just consuming caffeine period. This study was done at the University of Benin with 485 participants. Of the 485 students, 39.6% (192 students) were using caffeine at the time of the study. Although it is less than 50% of students, it is still a significant number of students using caffeine (Adayonfo, Akanni, & Ehimigbai, 2016).

These studies show that caffeine is highly favored and used in one way or another by many college students.

Anxiety…
Defining anxiety began in the 5th and 4th centuries B.C.E. when professionals began discussing sanity, insanity, and forms of fear. Among the Greek and later Roman civilization, social status and esteem was more important than emotions. To these civilizations, anxiety was the expectation of trouble such as sickness, war, loneliness, poverty, and mortality. Although anxiety was understood to be felt by every human, it was considered a bad characteristic if men could not successfully hide it, especially in times of war. An extreme disgrace would be if fear or anxiety could be detected from one man to another.

In the mid-4th century, the idea of fears and anxiety shifted to focus on humors. Four humors supposedly responsible for human functioning and wellbeing included blood, phlegm, black bile, and yellow bile. Anxiety was thought to be due to an excess of black bile. From the late 4th century to the 1st century, it was believed that distancing oneself from fear and unachievable desires would relieve anxiety and create a joyful life (Horwitz, 2013). In the Middle Ages, from the 5th to 17th centuries, anxiety was merged into the same category as melancholy and depression. In Chinese medicine during these centuries, anxiety was considered an issue stemming from the kidneys.

At the beginning of the 18th century, anxiety was seen as a natural part of human life once again. It was still being categorised with other feelings and states such as worry, fear, anger, panic, and depression. By the late 18th century, professionals started to distinguish between regular worries and constant anxiety. However, anxiety was still considered a mild mental problem resulting from mind abnormalities. Professional focus still lay on conditions deemed major at the time, requiring therapy and hospitalisation.

In the 19th century, Freud, inspired by the ideas of Hecker, proposed separating anxiety from being lumped in as a symptom in other disorders. He suggested that anxiety be categorised as anxiety neurosis, comprising four subcategories—avoidance of phobias, general irritability, consistent apprehension, and anxiety spasms. Soon after, Freud introduced categories of free-floating, generalized, and persistent anxiety.

The terminology of generalised anxiety appeared in the DSM-III in the 20th century. Before this, anxiety was part of what was referred to as psychoneuroticism (Guglielmo, Janiri, & Pozzi, 2014). However, due to the war, a non-medical view of anxiety gained significant attention, asserting anxiety as a normal response to societal situations requiring government action. According to this perspective, just like in the 18th century, anxiety was associated with everyday stressors such as overwork, marriage, raising children, and worldwide issues like war, international tension, and economic troubles. With many people self-diagnosing with anxiety during the 20th century, an outcry for remedies and treatments was rampant. Psychoanalysis was a small practice at the time, so people turned to their primary care physicians for relief (Horwitz, 2013).
In the 21st century, much like the 5th and 4th century Greek definition, the DSM-5 defines anxiety as the “anticipation of future threat,” and fear as “the emotional response to real or perceived imminent threat.” Anxiety has its own category in the DSM-5, with disorders in a spectrum all related to anxiety. These disorders include panic, phobia, agoraphobia, separation, social, post-traumatic stress, and generalized anxiety (American Psychiatric Association, 2016, pp. 1-7). Scientists are now looking at the mental and physical aspects of anxiety. The scientific investigation of the brain now includes trying to determine where in the brain anxiety stems from, and why it may cause physical symptoms. Neuroscientists have identified that the brain regions involved with anxiety include the prefrontal cortex, amygdala, and hippocampus. With these new findings, scientists can now create remedies and medications specific to neurotransmitters and brain functioning related to anxiety (Horwitz, 2013). Although in the 21st century anxiety is now a vast field of study, this research will concentrate on Generalized Anxiety Disorder and its symptoms in relation to college students’ caffeine intake.

Generalized Anxiety Disorder

To an extent, the 18th and 20th centuries were correct: feelings of worry and anxiety are natural. One may feel worry or anxiety about a life-changing event such as moving, a new job, an unexpected bill, or an unexpected illness. College students may worry about assignments due, working part-time, and family issues. Small amounts of worry and anxiety can be used as an encourager to stay motivated and finish tasks (Healey, 2014). However, Generalized Anxiety Disorder (GAD) is recognized when the feelings of worry and fear are overwhelming with no explanation or obvious cause.

People suffering from GAD find it impossible to complete daily tasks, focus, or to stop worrying once started, due to overwhelming fear and worry. Other symptoms of GAD include excessive bathroom use, profuse sweating, breathlessness, lightheadedness, irritability, racing heart, trouble focusing, being easily startled, fidgeting, body pains, and shaking. It is unknown how GAD is developed, however, it can worsen in stressful situations (“NIMH ?» Generalized Anxiety Disorder: When Worry Gets Out of Control,” 2016).

One of the first signs a person with GAD may notice is body pain or other changes in the body. The stomach may become upset, tension may develop in the neck and shoulders, and there may be feelings of fatigue but an inability to rest properly. People will visit their primary care doctors and want to get treated for body pain, but may not think to mention the symptom of constant worry or fear.
Some personality traits that may come with GAD include being unable to cope with the unknown, extreme effort at perfection, continuous checking on people or tasks, trouble making small decisions, excessive researching, excessive task creation, unwillingness to let others complete tasks, prolonging tasks, excluding oneself from new relationships, excluding oneself from new opportunities, distracting oneself from other tasks, and bestowing the responsibility of making decisions onto other people. Having GAD can be extremely debilitating to a person; one worry builds from another, creating a snowball effect of worrying that seems to never end. For example, a college student may have several assignments due at the same time. One may start to worry if assignments can be turned in on time, if one can achieve passing grades, then worry if one will graduate, then worry if one could find a good job or how much longer one would be in school, to how a marriage or relationship would work out if one did not have a degree, etc. The worry and fear would be so overwhelmingly hard to contain that the student may not get any work done. These symptoms must be manifested for half of a year to be considered GAD (Anxiety Disorders Association of British Columbia, 2017).

College Students, Caffeine, and Anxiety

The college experience is a unique one for all who partake in it. If one is living on campus or living away from parental influences, everyday life decisions fall onto that person, and independence is experienced. College students have the freedom to dictate every aspect of their lives including eating, drinking, class scheduling, activities, sleeping, completion of assignments, and leisure time (Scheiwe, 2003). The freedom, demands, and scheduling during college years can become stressful or worrisome. Some colleges typically offer academic advisors, success advisors, and counselors to help students succeed and cope with college life. Among colleges, these resources are not advertised well enough to students, and those who are aware of them may view seeking these extra resources as a nuisance or unhelpful (Bhujade, 2017). However, in a study done by Wig, et al., 1969, 68 students were placed in counseling, 50% of the students reported finding difficulty in concentrating, 24% reported feelings of sadness, 23.5% reported head pain, and 23.5% reported feeling nervous (as cited in Bhujade, 2017).

The caffeine intake of these students in this study is unknown. However, in modern times with early morning classes, late-night papers, and other daily demands, caffeine consumption is an everyday ritual for many college students because of the advertised outcomes caffeine can have on a person. Self-helps like caffeine consumption, smoking, overindulgence in food, exercise, intimate relationships, and drinking are more common amongst college students because it takes less time and effort than seeking out other forms of help. Students may also use self-help methods instead of academics out of embarrassment of being unable to cope with college life (Scheiwe, 2003).

College Student Beliefs and Experiences with Caffeine
The beliefs about caffeine and experiences with it amongst college students can vary depending on where they are from, what university they attend, what religious beliefs they hold, and how caffeine consumption has affected them in the past. For example, according to BBC News in September 2017, Mormon college, Brigham Young University, just lifted its almost 70-year ban on caffeine. The university now sells soda with caffeine in it but still does not allow highly caffeinated drinks such as energy drinks. This means that due to religious views and the university they attended, the students at this university were excluded from caffeine usage. The students had been challenging the university’s decision since 2012. They wanted the right to choose to consume caffeine since it did not interfere with the university’s and the Mormon religion’s standard of abstaining from alcohol and maintaining purity (BBC News, 2017). At Marshall University, a study was done on 300 freshmen to explore their beliefs about caffeine. In this study, 79.7% (239 students) believed caffeine was harmful to them, 43% (129 students) believed caffeine disturbs coordination, and 82.3% (247 students) believed caffeine is addictive. However, contrary to those beliefs, this study showed that 65% (195 students) drank caffeine daily, 76% (229 students) believed caffeine increased wakefulness, and 76.3% (229 students) used caffeine to stay awake (McIlvain, Noland, & Bickel, 2011). In a study done by Parker-Pope in 2008, one-third of 12-24-year-olds reported using energy drinks because they were fond of the taste, wanted to stay awake for night study sessions, or wanted to increase overall wakefulness throughout the day (as cited by Liberatore, 2009).
Another study was conducted, focusing on energy drink consumption and reasons, in the Central Atlantic part of the U.S. with 496 students. In this study, 67% of students used energy drinks due to lack of sleep, 65% wanted to increase energy, 50% used caffeine in preparation for studying or completing large assignments, and 54% used them while drinking alcohol. Also, in this study, 29% felt an increase in energy followed by an extreme plummet, 19% reported feeling heart palpitations, and 22% reported experiencing headaches (Malinauskas, Aeby, Overton, Carpenter-Aeby, Barbara-Heidal, 2012).

Another study, conducted at a university in Pakistan, measured caffeine intake and academic performance. This study consisted of 384 students; 71.5% believed caffeine increased academic performance, 71% believed caffeine increased self-efficacy, 70% reported it increased wakefulness, and 22% believed caffeine increased IQ. However, contrary to the students’ beliefs, 53.8% of the students achieved a GPA above 3.0, while the remaining scored below a 3.0 GPA. This result was average and demonstrated a low correlation between increased GPA and caffeine consumption (Khan, Nisar, Naqvi & Nawab, 2017).

In a study conducted in Turkey at a university, 156 students were surveyed for caffeine intake and withdrawal symptoms such as headache, anxiety, and inability to concentrate, etc. In the study, student’s intake of over 200mg of caffeine daily resulted in 20.7% reporting headaches, 27.2% fatigue, 18.1% irritability, 32.4% drowsiness, 16.8% anxiety, 14.2% inability to concentrate, and 28.5% reported no symptoms (K??§er, 2010).

In this study, I hypothesize that caffeine consumption increases generalized anxiety symptoms in college students compared to those who do not consume caffeine.

References

1. Adayonfo, E. O., Akanni, O. O., & Ehimigbai, M. (2016). Profile of undergraduate student caffeine users/abusers in Benin City, Nigeria.IFE Psychologia: An International Journal,24(2), 216-223
2. Alpert, P.T. (2012). The health low down on caffeine. Home Health Care Management & Practice 24, 3, 156 “ 158. https://doi.org/10.1177/1084822311435543
3. American Psychiatric, A. (2016).Anxiety Disorders: DSM-5?® Selections. Arlington, VA: American Psychiatric Publishing.
4. Anxiety Disorders Association of British Columbia. (2017). What is Generalized Anxiety Disorder? Retrieved from https://www.anxietybc.com/adults/generalized-anxiety-disorder
5. BBC News. (2017, September 21). Mormon college ends ban on caffeine sodas. Retrieved from http://www.bbc.com/news/world-us-canada-41351251
6. Bhujade, V. M. (2017). Depression, anxiety and academic stress among college students: A brief review.Indian Journal of Health & Wellbeing,8(7), 748-751.
7. Caffeine Informer. (n.d.). Retrieved from https://www.caffeineinformer.com/
8. Cappelletti, S., Daria, P., Sani, G., & Aromatario, M. (2015). Caffeine: cognitive and physical performance enhancer or psychoactive drug?Current Neuropharmacology,13(1), 71 88. http://doi.org/10.2174/1570159X13666141210215655
9. Ettinger, J. (2011, December 2). Need A Lift or A Jolt? Natural Vs. Synthetic Caffeine. Retrieved from http://www.organicauthority.com/health/need-a-lift-or-a-jolt-the-important-differences-between-natural-and-synthetic-caffeine-natural-caffeine-vs-synthetic-why-the-difference-is-important.html
10. Goodman, B. A. (2012).Coffee Consumption and Health. New York: Nova Science Publishers, Inc.
11. Guglielmo, R., Janiri, L., & Pozzi, G. (2014).New Perspectives on Generalized Anxiety Disorder. New York: Nova Science Publishers, Inc.
12. Healey, J. (2014).Understanding Anxiety. Thirroul, N.S.W: Spinney Press.
13. Horwitz, A. V. (2013).Anxiety: A Short History. Baltimore: Johns Hopkins University Press.
14. Khan, N., & Mukhtar, H. (2013). Tea and health: Studies in humans.Current Pharmaceutical Design,19(34), 61416147.
15. Khan, S.K., Nisar, N., Naqvi, S.A.A., & Nawab, F., (2017). Caffeine consumption and academic performance among medical students of Dow University of Health Science (DUHS), Karachi, Pakistan.Annals of Abbasi Shaheed Hospital & Karachi Medical & Dental College,22(3), 179-184.
16. Kuher, N. (2010). The relationship between daily caffeine consumption and withdrawal symptoms: a questionnaire-based study.Turkish Journal of Medical Sciences,40(1), 105-108. doi:10.3906/sag-0809-26
17. Liberatore, Stephanie. (2009). Q: With the increasing popularity of energy drinks, I wonder are these drinks safe? How do they affect teens? The science teacher. Science in Context, http://link.galegroup.com/apps/doc/A193960685/SCIC?u=pl3540&xid=b3920874.
18. Al Ghali, R., Al Shaibi, H., Al Majed, H., & Haroun, D. (2017). Caffeine consumption among Zayed University students in Dubai, United Arab Emirates: A Cross-Sectional study.Arab Journal of Nutrition and Exercise (AJNE), 1(3), 131-141. doi: https://doi.org/10.18502/ajne.v1i3.1230
19. Malinauskas, B. M., Aeby, V. G., Overton, R. F., Carpenter-Aeby, T., & Barber-Heidal, K. (2007). A survey of energy drink consumption patterns among college students.Nutrition Journal,635-41. doi:10.1186/1475-2891-6-35
20. Massey, J. L. (2016).Coffee: Production, Consumption and Health Benefits. New York: Nova Science Publishers, Inc.
21. McIlvain, G. E., Noland, M. P., & Bickel, R. (2011). Caffeine consumption patterns and beliefs of college freshmen.American Journal of Health Education,42(4), 235-244.
22. Monteiro, J., Alves, M., Oliveira, P., & Silva, B. (2016). Structure-bioactivity relationships of methylxanthines: Trying to make sense of all the promises and the drawbacks.Molecules,21(12), 974. http://dx.doi.org/10.3390/molecules21080974
23. NIMH, (2016). Generalized Anxiety Disorder: When Worry Gets Out of Control. Retrieved from https://www.nimh.nih.gov/health/publications/generalized-anxiety-disorder-gad/index.shtml
24. Newton, D. E. (2014). Caffeine. In K. L. Lerner & B. W. Lerner (Eds.), The Gale Encyclopedia of Science (5th ed.). Farmington Hills, MI: Gale. http://ezproxy.eastern.edu:4213/apps/doc/CV2644030370/SCIC?u=pl3540&xid=e7ceaa0c

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