Caffeine Consumption: A Literature Review

Victoria Ardoin and Courtney Huck Hebert McNeese State University

Caffeine is one of the most consumed substances among populations around the world, with 82-92% of adults in North America regularly consuming caffeine (Armstrong, 2002). Research shows that consumption has increased dramatically over the last decade through both coffee consumption and other caffeine-containing beverages (McIlvain et al., 2011). Armstrong reported that in the U.S., the average adult coffee drinker consumes 200-400 mg of caffeine (2-4 cups of coffee) each day and that 20-30% of these adults consume up to 600 mg per day. Another point of concern is that energy drinks are on the rise and though they are defined as having beneficial propriety blends, some are known to have very high amounts of caffeine (Branum et al., 2013). Caffeinated energy drinks, as defined De Sanctis et al. (2017), are beverages that contain caffeine and varied other substances, such as guarana, taurine, ginseng, vitamins, herbal supplements, and sugar. They are advertised as increasing energy, improving athletic performance, concentration, reactions, wakefulness, attention, emotions, and metabolism. Safe limits of caffeine consumption are still undetermined, but data suggest that maximum recommended intake of caffeine per day is around 100 mg/day in adolescents and up to 400 mg/day in adults (De Sanctis et al., 2017). This literature review intends to examine caffeine consumption trends among young adults, awareness and perceptions of its use, and overall health effects.

In a study by Mahoney et al. (2019), it was determined that caffeine, in any form, was consumed by 92% of students from five geographically dispersed United States universities. The researchers included a total of 1,248 students from Louisiana State University in Louisiana (LSU; N = 301); Kent State University in Ohio (Kent State; N = 286); University of Massachusetts Amherst in Massachusetts (UMASS; N = 238); California State University Fullerton in California (Cal State; N = 212); and Tufts University in Massachusetts (Tufts; N = 211). Mean daily caffeine consumption for all students, including non-consumers, was 150 mg/d with a mean intake of 173 mg/d among caffeine users. The researchers analyzed intake from coffee, tea, soft drinks, energy drinks, gums, and medication, and found that coffee was the main source of caffeine intake in male (120 mg/d) and female (111 mg/d) consumers. Mahoney et al. (2019) found that students, especially women, tend to consume somewhat more caffeine than the general population of individuals aged 19-30 years old but also consumed less than individuals aged 31-50 years old.

From a study conducted by Tran et al. (2016), research focused on caffeine consumption among U.S. teenagers (13-17y), young adults (18-24y), and adults (25-29y) for a 10-year period utilizing NHANES 2003-12 for examination purposes. The goal of this study was to determine whether caffeine habits were within safe limits and void of any adverse effects. The researchers found that mean caffeine intake per consumption occasion was equivalent between coffee and energy drinks for teenagers and young adults. They determined that caffeine intake from energy drinks was only statistically significant for ages 18-24 years of age, accounting for a total of <9% caffeine intake. Tran et al. (2016) used linear regression models in order to analyze the relationships between caffeine intake from energy drinks against caffeine from coffee, as well as tea and soda among energy drink consumers in the upper 50th percentile, which showed a statistically significant inverse relationship (R2 = 28%, coffee β = −0.35, p < 0.001; tea: β = −0.44, p < 0.001; soda: β = −0.22, p = 0.036). They concluded from this study that mean caffeine consumption was within considerably safe and moderate levels established by health authorities among teenagers and young adults, and that despite the introduction of new sources of caffeine to the marketplace, there are persistently small numbers of

energy drink consumes, with the majority of dietary caffeine for the general population coming from coffee, tea, and soft drinks.

McIlvain et al. (2011) designed a study with purposes of determining the amount of caffeine consumed by a sample of college students, beliefs regarding caffeine consumption, reported perceived benefits and adverse effects of caffeine consumption, reasons for consuming caffeine, and predictors of caffeine consumption. They utilized an anonymous survey which was administered to 300 freshmen students, 118 men (39.3%) and 182 women (60.7%), attending a southeastern university. In their study, they note that the researchers at Johns Hopkins University School of Medicine reported that moderate doses (200-300 mg/day) of caffeine for adults are not harmful, but doses of more than 500-600mg/day can cause side effects. Shockingly, they found that students in the study had a mean caffeine consumption of 849.86 mg/day and there was 12.1 mg of caffeine consumed per kg. of body weight. In order to reach this value, they included an exhaustive list of drinks containing caffeine, and made sure to include how many of each size was consumed daily by those that completed the survey. The values found from this study was a point of interest, as it is an outlier compared to the other studies, which found average consumption was around 150-300 mg/day. This could indicate this study was either reflective of increasing caffeine consumption among college students, that this particular group of students indulged in caffeine-containing beverage consumption more, or that the study design and methods well-executed transparently gathering caffeine consumption data among college students.

In a cross-sectional study by Al-turki et al. (2016) utilized a 26-question self-administered questionnaire distributed to 550 medical students (275 male and 275 female). The objective of their study was to estimate the daily amount of caffeine consumption among medical students due to medical students utilizing it more than other students to overcome the stress they face due to studying. The researchers found that 97.5% of medical students they surveyed were consuming caffeine while only 2.5% were not. They also found that low intake of caffeine users represented the majority (49.3%), with moderate (28%) and high (22.7%) caffeine intake users not far behind. The researchers of this study concluded a very high percentage of caffeine consumers among medical students; however, the use was still on the safe side. Hidiroglu et al. (2013) researched caffeine consumption from medical students but looked at energy drink consumption. The objective of their study was to determine the frequency and pattern of energy drink consumption among medical students, their knowledge of its effects and side effects, and to see its relationship with alcohol and cigarette use. From their results, they found that the mean age of the 390 students in the study was 20.98±1.96 years (range: 16-27). They determined that 32.6% had consumed energy drinks at least once and 18.8% more than once. The researchers conclude that consumption of energy drinks among medical students was common and casual.

Literature indicates that caffeine consumption continues to rise. While this trend grows, the caffeine consumption levels are remaining safe. The manner in which it is consumed varies somewhat; however, the research supports that coffee, tea, and soda remain the popular choices. Further investigation should be done to gather more information on the consumption of caffeine in specific age demographics.

A variety of reasons for use of caffeine have been reported in literature, such as surgeons utilizing caffeine to reduce fatigue, athletes using caffeine to enhance physical performance, and adolescents reported they use caffeine for more energy (Mahoney et al., 2019). In a meta-analyses study conducted by Coso et al. (2020), researchers found that 89.2% of those who consumed caffeine had reasons that were related to the use of this beverage to modify one or more health outcomes. There are many reasons college students are including caffeine within their diet, but most commonly, it is assumed that it is due to increasing focus and awareness, minimizing effect of drowsiness to feel more awake, or to improve mood. Several studies looked at college students to determine what reasons they were including caffeine in their diet and what their perceived

beliefs and effectiveness of caffeine were. Mahoney et al. (2019) found that students had multiple reasons for consuming caffeine, including to feel awake (79%), enjoy the taste (68%), the social aspects of consumptions (39%), improve concentration (31%), increase physical activity (27%), improve mood (18%), and alleviate stress (9%). McIlvain et al. (2011) found that the reported reasons college students were consuming caffeine was that they believed it would keep them awake (76.0%), help them wake up in the morning (59.3%), and help them concentrate (27.7%).

In an honors thesis paper by Olsen (2013), two focus group interviews and a survey were administered to conduct research on University of New Hampshire campus. She found that the reasons students were consuming caffeine included staying awake, getting good grades, being able to focus, and being better able to socialize. From another study that utilized focus groups and survey administration in order to analyze caffeine intake patterns among college students, researchers Malinauskas et al. (2007) wanted to determine how energy drinks, targeted to the 18 to 35 year old consumer, made an impact. They found that the majority of users consumed energy drinks for insufficient sleep (67%), to increase energy (65%), and to drink alcohol while partying (54%). They concluded from their research that using energy drinks is a popular practice among college students for a variety of situations, but future research should identify if college students recognize the amounts of caffeine present in the wide variety of caffeine-containing products that they are consuming, the amounts of caffeine that they are consuming in various situations, and the physical side effects associated with caffeine consumption.

There are common themes within the research. The most apparent is the perceptions that are associated with consuming caffeine. These reasons are centered on needing energy, help focusing, and improving ones mood. It is recommended that more research continue to study the perceptions of caffeine use in a variety of age demographics.

The review of literature indicates caffeine consumption is rising. Multiple studies support the prime source of caffeine is coffee. This appears to be especially true for traditional college-aged populations. As the research continues to support a growing trend of caffeine consumption, the need for continued studies grows. Although caffeine consumption among young adults remains relatively safe, misinformed perceptions of health benefits will likely result in increased caffeine use. One thing that the present data lack is how increased caffeine consumption may be related to poor dietary intake and choices among consumers. This specific observation requires a more in depth look in future research.

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