Intake of caffeine from all sources and reasons for use by college students

Open AccessPublished:April 10, 2018DOI:https://doi.org/10.1016/j.clnu.2018.04.004

      Summary

      Background & aims

      Caffeine intake in a convenience sample of U.S. college students (N = 1248) was surveyed at five geographically-dispersed United States (U.S.) universities.

      Methods

      Intake from coffee, tea, soft drinks, energy drinks, gums, and medications was assessed. Associations between caffeine intake and demographic variables including sex, age, race/ethnicity, family income, general health, exercise, weight variables and tobacco use were examined. Reasons for use of caffeine-containing products were assessed.

      Results

      Caffeine, in any form, was consumed by 92% of students in the past year. Mean daily caffeine consumption for all students, including non-consumers, was 159 mg/d with a mean intake of 173 mg/d among caffeine users. Coffee was the main source of caffeine intake in male (120 mg/d) and female (111 mg/d) consumers. Male and female students consumed 53 vs. 30 mg/d of caffeine in energy drinks, respectively, and 28% consumed energy drinks with alcohol on at least one occasion. Students provided multiple reasons for caffeine use including: to feel awake (79%); enjoy the taste (68%); the social aspects of consumption (39%); improve concentration (31%); increase physical energy (27%); improve mood (18%); and alleviate stress (9%).

      Conclusions

      As in the general U.S. population, coffee is the primary source of caffeine intake among the college students surveyed. Energy drinks provide less than half of total daily caffeine intake but more than among the general population. Students, especially women, consume somewhat more caffeine than the general population of individuals aged 19–30 y but less than individuals aged 31–50 y.

      Keywords

      1. Introduction

      Eighty-nine percent of the United States (U.S.) population regularly consumes caffeine [
      • Fulgoni III, V.L.
      • Keast D.R.
      • Lieberman H.R.
      Trends in intake and sources of caffeine in the diets of U.S. Adults: 2001–2010.
      ]. Coffee is the primary source of caffeine in the U.S. diet, but tea, carbonated soft drinks, hot cocoa, chocolate milk and chocolate candy, energy drinks and some dietary supplements also contain caffeine and the caffeine content of these products varies considerably [
      • Fulgoni III, V.L.
      • Keast D.R.
      • Lieberman H.R.
      Trends in intake and sources of caffeine in the diets of U.S. Adults: 2001–2010.
      ,
      • Barone J.J.
      • Roberts H.R.
      Caffeine consumption.
      ,
      • Mitchell D.C.
      • Knight C.A.
      • Hockenberry J.
      • Teplansky R.
      • Hartman T.J.
      Beverage caffeine intakes in the U.S..
      ].
      A number of surveys have quantified caffeine intake in the United States. The USDA Continuing Surveys of Food Intakes by Individuals (CSFII) conducted in 1994–1996 and 1998 sampled approximately 18,000 individuals in the U.S. [
      • Frary C.D.
      • Johnson R.K.
      • Wang M.Q.
      Food sources and intakes of caffeine in the diets of persons in the United States.
      ]. Eighty-seven percent of respondents consumed caffeine, and average intake of consumers was 193 mg/day. The major source of caffeine was coffee followed by soft drinks and tea. In the 1999 Share of Intake Panel (SIP) survey, coffee, soft drinks and tea provided the largest amounts of caffeine in the diet [
      • Knight C.A.
      • Knight I.
      • Mitchell D.C.
      • Zepp J.E.
      Beverage caffeine intake in US consumers and subpopulations of interest: estimates from the share of intake panel survey.
      ]. The Kantar Worldpanel (KWP) Beverage Consumption Panel survey (formerly the SIP) quantified caffeine intake from beverages in the U.S. between October 2010 and September 2011 [
      • Mitchell D.C.
      • Knight C.A.
      • Hockenberry J.
      • Teplansky R.
      • Hartman T.J.
      Beverage caffeine intakes in the U.S..
      ]. Consistent with previous findings, approximately 85% of respondents consumed some type of caffeine-containing beverage, and 98% of all caffeine was consumed in the form of coffee, tea, carbonated soft drinks and energy drinks. A recent report based on data collected from 2001 to 2010 in a large, nationally-representative U.S. survey, the National Health and Nutrition Examination Survey (NHANES), found that 89% of U.S. adults regularly consume caffeine with usual intake by caffeine consumers being 211 mg/d [
      • Fulgoni III, V.L.
      • Keast D.R.
      • Lieberman H.R.
      Trends in intake and sources of caffeine in the diets of U.S. Adults: 2001–2010.
      ]. Coffee (64%), soft drinks (18%) and tea (16%) were the main sources of caffeine in the diet [
      • Fulgoni III, V.L.
      • Keast D.R.
      • Lieberman H.R.
      Trends in intake and sources of caffeine in the diets of U.S. Adults: 2001–2010.
      ].
      A variety of reasons for use of caffeine have been reported in the literature. Surgeons have been reported to use caffeine to reduce fatigue [
      • Franke A.G.
      • Bagusat C.
      • McFarlane C.
      • Tassone-Steiger T.
      • Kneist W.
      • Lieb K.
      The use of caffeinated substances by surgeons for cognitive enhancement.
      ]. Athletes report using caffeine to enhance their physical performance [
      • Desbrow B.
      • Leveritt M.
      Well-trained athletes' knowledge, insight, and experience of caffeine use.
      ]. Adolescents state they use caffeine to provide more energy, for the taste of the product and for image enhancement [
      • Turton P.
      • Piche L.
      • Battram D.S.
      Adolescent attitudes and beliefs regarding caffeine and the consumption of caffeinated beverages.
      ].
      Energy drinks are a relatively new source of caffeine on the market and are popular among young people, especially young males. They are controversial with some scientists expressing concern regarding their safety although others disagree [
      • Reissig C.J.
      • Strain E.C.
      • Griffiths R.R.
      Caffeinated energy drinks–a growing problem.
      ,
      • Turnbull D.
      • Rodricks J.V.
      • Mariano G.F.
      Neurobehavioral hazard identification and characterization for caffeine.
      ]. One component of energy drinks that is known to affect behavior is caffeine so their use should be considered in the context of consumption of all caffeine-containing products [
      • McLellan T.M.
      • Lieberman H.R.
      Do energy drinks contain active components other than caffeine?.
      ]. Energy drinks also usually contain many other ingredients such as taurine, various vitamins and carbohydrates that may be bioactive [
      • McLellan T.M.
      • Lieberman H.R.
      Do energy drinks contain active components other than caffeine?.
      ]. Other caffeine-containing products such as coffee, tea and cola drinks also contain a variety of other potentially bioactive compounds. A survey of energy drink intake, conducted with a representative U.S. sample, reported 4% of individuals consumed caffeine in energy drinks [
      • Mitchell D.C.
      • Knight C.A.
      • Hockenberry J.
      • Teplansky R.
      • Hartman T.J.
      Beverage caffeine intakes in the U.S..
      ]. Recent NHANES findings indicate only 1%–2% of total caffeine intake in the adult U.S. population was from energy drinks [
      • Fulgoni III, V.L.
      • Keast D.R.
      • Lieberman H.R.
      Trends in intake and sources of caffeine in the diets of U.S. Adults: 2001–2010.
      ,
      • Drewnowski A.
      • Rehm C.D.
      Sources of caffeine in diets of US children and adults: trends by beverage type and purchase location.
      ]. Energy drink consumption appears to be particularly common among college students [
      • Norton T.R.
      • Lazev A.B.
      • Sullivan M.J.
      The “buzz” on caffeine: patterns of caffeine use in a convenience sample of college students.
      ,
      • Jeffers A.J.
      • Vatalaro Hill K.E.
      • Benotsch E.G.
      Energy drinks, weight loss, and disordered eating behaviors.
      ,
      • Gallucci A.R.
      • Martin R.J.
      • Morgan G.B.
      The consumption of energy drinks among a sample of college students and college student athletes.
      ,
      • Emond J.A.
      • Gilbert-Diamond D.
      • Tanski S.E.
      • Sargent J.D.
      Energy drink consumption and the risk of alcohol use disorder among a national sample of adolescents and young adults.
      ] but accounted for less than 9% of total caffeine consumed by U.S. adults aged 18–24 y [
      • Tran N.L.
      • Barraj L.M.
      • Bi X.
      • Jack M.M.
      Trends and patterns of caffeine consumption among US teenagers and young adults, NHANES 2003–2012.
      ]. About one-third of college students surveyed reported consuming at least one energy drink over the previous 30 days [
      • Jeffers A.J.
      • Vatalaro Hill K.E.
      • Benotsch E.G.
      Energy drinks, weight loss, and disordered eating behaviors.
      ].

      1.2 Present study

      Given the rapid growth of the energy drink industry, whose marketing is often geared toward young adults [
      • Heckman M.A.
      • Sherry K.
      • Gonzalez De Mejia E.
      Energy drinks: an assessment of their market size, consumer demographics, ingredient profile, functionality, and regulations in the United States.
      ], quantification of caffeine intake and its sources by U.S. college students warrants additional investigation. National surveys such as the Kantar Worldpanel and NHANES have not typically examined college students as a subgroup of the population. Previous research in this area has suggested use of energy drinks by college students could contribute to a number of adverse outcomes. For example, it has been suggested energy drink consumption by college students is associated with lower sleep quantity and quality as well as next day sleepiness [
      • Patrick M.E.
      • Griffin J.
      • Huntley E.D.
      • Maggs J.L.
      Energy drinks and binge drinking predict college students' sleep quantity, quality, and tiredness.
      ]. It has also been suggested that episodic (binge) alcohol use is associated with energy drink consumption among college students [
      • Gallucci A.R.
      • Martin R.J.
      • Morgan G.B.
      The consumption of energy drinks among a sample of college students and college student athletes.
      ]. In addition, it has been reported that undergraduates who are attempting to lose weight are more likely to use energy drinks [
      • Jeffers A.J.
      • Vatalaro Hill K.E.
      • Benotsch E.G.
      Energy drinks, weight loss, and disordered eating behaviors.
      ]. Therefore, this study assessed caffeine intake from a wide variety of caffeinated products including coffee, tea, colas and other soft drinks, energy drinks, gums and medications among a convenience sample of college students at 5 geographically-dispersed U.S. universities. The reasons college students reported using caffeine-containing products were also assessed. In addition, associations between caffeine intake and demographic variables such as sex, age, race/ethnicity, family income, general health, exercise and weight variables and tobacco use were examined.

      2. Methods

      For this study, a total of 1248 students from five U.S. universities were sampled in 2009 and 2010: 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). The schools were chosen to be representative of the major types of American 4-year colleges and universities, including public and private institutions, residential and commuter schools, and various geographic regions of the U.S. A convenience sample of college students were recruited through an information booth (UMASS), online (Cal State and Tufts), or in the classroom (Cal State, Kent State and LSU). Students at UMASS and Tufts were given an incentive of $10 to complete the survey and students at LSU were provided with classroom-based extra credit incentive. The study was approved by the USARIEM Human Subjects Institutional Review Board and the review boards of the colleges surveyed. The data collected in this survey were also used to assess dietary supplement intake of college students [
      • Lieberman H.R.
      • Marriott B.P.
      • Williams C.
      • Judelson D.
      • Glickman E.G.
      • Geiselman P.J.
      • et al.
      Patterns of dietary supplement use among college students.
      ]. Similar surveys of U.S. Army, Air Force and Coast Guard populations have been conducted and, like this survey, also concurrently assessed intake of dietary supplements [
      • Austin K.G.
      • Price L.L.
      • McGraw S.M.
      • Lieberman H.R.
      Predictors of dietary supplement use by U.S. Coast guard personnel.
      ,
      • Austin K.G.
      • Price L.L.
      • McGraw S.M.
      • Leahy G.
      • Lieberman H.R.
      Demographic, lifestyle factors and reasons for use of dietary supplements and sports nutrition products by Air Force Personnel.
      ,
      • Lieberman H.R.
      • Stavinoha T.
      • McGraw S.
      • White A.
      • Hadden L.
      • Marriott B.
      Use of dietary supplements among active duty US Army soldiers.
      ,
      • Lieberman H.R.
      • Stavinoha T.
      • McGraw S.
      • White A.
      • Hadden L.
      • Marriott B.
      Caffeine use among active duty US Army soldiers.
      ].

      2.1 Variables

      The self-report survey instrument included detailed questions on types of caffeine-containing beverages, gums and medications consumed, and the amount and frequency of consumption. A diverse variety of 31 specific caffeine-containing products were included as response options in the survey instrument. Respondents were asked to indicate serving size and frequency of use (number of times consumed per day, week, month, or year) for each product they regularly consumed. Participants were asked to write in caffeine-containing beverages they used that were not specifically identified in the questions on the survey. For data analysis, individual caffeine beverage types were grouped into the following categories: coffee, tea, sodas (regular and diet), energy drinks and other. All categories were combined to arrive at aggregate caffeine intake for the total sample including students who were not caffeine consumers and identify regular users of caffeine-containing products. Aggregate use was calculated as average daily intake for all students surveyed. Regular users were defined as those consuming any caffeine-containing products at least once a week. Identical procedures were employed to analyze data collected from U.S. Army soldiers and Air Force personnel who completed a nearly-identical survey [
      • Lieberman H.R.
      • Stavinoha T.
      • McGraw S.
      • White A.
      • Hadden L.
      • Marriott B.
      Caffeine use among active duty US Army soldiers.
      ,
      • Knapik J.J.
      • Austin K.G.
      • McGraw S.
      • Leahy G.D.
      • Lieberman H.R.
      Caffeine consumption among active duty United States Air Force personnel.
      ].
      As described previously, the survey collected data on a number of sociodemographic and lifestyle factors including: sex, age, race/ethnicity, family income, general health, aerobic exercise duration, whether the individual exercised with a team, whether the individual was attempting to gain or lose weight, and tobacco use [
      • Lieberman H.R.
      • Marriott B.P.
      • Williams C.
      • Judelson D.
      • Glickman E.G.
      • Geiselman P.J.
      • et al.
      Patterns of dietary supplement use among college students.
      ]. Self-reported height and weight were collected and body mass index (BMI) was calculated (BMI = mass in kilograms divided by squared height in meters, rounded to the nearest tenth). Individuals with BMI <18.5 were considered underweight, individuals with BMI ≥18.5 and < 24.9 were considered in the normal weight range, while a BMI ≥25.0–29.9 was considered overweight and individuals with BMI ≥30.0 were classified as obese [
      • Kuczmarski M.
      • Kuczmarski R.
      • Najjar M.
      Effects of age on validity of self-reported height, weight, and body mass index: findings from the third National Health and Nutrition Examination Survey, 1988–1994.
      ,
      • Flegal K.M.
      • Carroll M.D.
      • Ogden C.L.
      • Johnson C.L.
      Prevalence and trends in obesity among US adults, 1999–2000.
      ,
      • Ogden C.L.
      • Carroll M.D.
      • Curtin L.R.
      • McDowell M.A.
      • Tabak C.J.
      • Flegal K.M.
      Prevalence of overweight and obesity in the United States, 1999–2004.
      ]. To assess reasons for general caffeine consumption (not use of any specific beverage), a question listing nine possible reasons was included in the survey. Participants could specify other reasons as well (see Table 4).

      2.2 Survey administration

      The survey was administered on-site by project staff at participating universities. Completed surveys were returned to the project team who scanned and tabulated responses using ScanTools® Plus with ScanFlex™ (version 6.301, 2006, Scantron Corporation, Eagan, Minnesota).

      2.3 Calculation of daily caffeine intake

      Based on information reported on product type, size and frequency of use, daily caffeine consumption was calculated using data on the amount of caffeine in specific product types. Sources of caffeine content in specific products included company websites and a database compiled by the authors on caffeine content of various brands and types of soda, coffee and energy drinks based on product labels, product websites, and other reliable online sources of caffeine contents [
      • CaffeineInformer
      ,
      • U.S. Department of Agriculture
      USDA food composition database.
      ]. Based on response distribution and inconsistent reporting, individuals reporting total caffeine consumption >2000 mg/day were excluded; this corresponded to less than 1% of the sample [
      • Lieberman H.R.
      • Stavinoha T.
      • McGraw S.
      • White A.
      • Hadden L.
      • Marriott B.
      Caffeine use among active duty US Army soldiers.
      ].

      2.4 Statistics

      The SAS (Version 9.2, 2008, SAS Institute, Cary, NC) statistical software program was used for data analysis (SAS Institute Inc. 2004). Pearson chi-square tests were used to assess the association between respondent sociodemographic characteristics and overall caffeine intake from all sources assessed, as well as from specific sources of caffeine. For caffeine users, analysis of variance (ANOVA) was used to assess the association between student sociodemographic and lifestyle characteristics and amount of caffeine consumed, overall from all sources and for specific caffeine sources; these ANOVA models were adjusted for survey site. Based on these results, multiple linear regression was used to examine the independent effects of student characteristics on caffeine consumption among caffeine users.

      3. Results

      The sociodemographic and lifestyle characteristics of respondents and intake of caffeine products as related to sociodemographic and lifestyle characteristics as totaled across the five universities are presented in Table 1. A majority of the respondents were female (64.2%), 20–22 years old (52.2%), non-Hispanic whites (69.4%), and nearly half reported family income $25,000 – $99, 999 (49.0%). In comparison, the majority of the general U.S. postsecondary education population at the time were female (57%), 24 yrs old or less (57%), and white (61%) [
      • National Center for Education Statistics
      Digest of education statistics 2015 NCES 2016-014.
      ]. The majority of volunteers in this study had a “normal” BMI of 18.5–24.9 (68.2%). A large percentage of participants exercised more than 300 min/wk (30.3%) and over a third exercised in an intramural or extramural team setting (41.1%). Most students were trying to maintain weight (46.5%) and had never used tobacco products (71.6%).
      Table 1Sample size and intake of caffeine in any form and in specific products over the past year, according to selected sociodemographic and lifestyle characteristics.
      N
      The total number of respondents with the given characteristic in the row, i.e. the denominator for all the percentages in that row.
      %Any caffeineCoffeeTeaSodaEnergy DrinksOther
      %
      The percent of respondents with the given characteristic in the row who indicated any consumption of caffeine from the source shown in the column i.e. row percents.
      P
      Pearson chi-square statistic for overall association between given row characteristic and any consumption of caffeine from the source shown in the column.
      %P%P%P%P%P
      Overall124891.7%72.0%61.4%68.8%36.4%12.2%
      Sex
       Male44735.8%87.2%<0.00161.1%<0.00148.3%<0.00167.8%0.55239.4%0.1007.8%<0.001
       Female80164.2%94.3%78.0%68.7%69.4%34.7%14.6%
      Age years
       16 to 1940132.1%93.5%0.09173.6%0.65867.6%0.00271.1%0.50037.2%0.24812.7%0.236
       20 to 2265152.2%91.7%71.4%59.9%67.7%37.5%10.9%
       23+19615.7%88.3%70.4%53.6%67.9%31.1%15.3%
      Race/ethnicity
       Non-hispanic white86669.4%92.0%0.47672.9%<0.00159.7%0.17670.1%0.20936.5%0.20912.8%0.245
       Non-hispanic black887.1%90.9%51.1%69.3%71.6%34.1%13.6%
       Hispanic/Latino1249.9%93.5%79.0%59.7%68.5%34.7%12.9%
       Asian1129.0%87.5%71.4%65.2%62.5%32.1%5.4%
       Other584.6%93.1%75.9%70.7%58.6%50.0%12.1%
      Family income
       < $25,000939.0%88.2%0.66766.7%0.71858.1%0.91164.5%0.06239.8%0.54716.1%0.751
       $25k – $99,99950649.0%91.3%72.1%60.5%66.6%34.0%12.8%
       $100k – $200k31330.3%92.0%72.5%61.3%70.3%37.7%11.8%
       >$200,00012011.6%92.5%72.5%58.3%78.3%38.3%13.3%
      General health
       Excellent43634.9%91.3%0.56870.2%0.59362.6%0.21563.1%0.00331.4%0.02310.6%0.020
       Good73458.8%91.7%72.9%59.8%71.4%38.7%12.1%
       Fair/poor786.3%94.9%73.1%69.2%76.9%42.3%21.8%
      Body mass index
       <18.5483.9%97.9%0.02177.1%0.29768.8%0.00168.8%0.08537.5%0.06716.7%0.001
       18.5–24.983368.2%92.8%73.6%63.1%68.4%35.7%12.1%
       25.0–29.925921.2%88.0%68.0%51.7%66.8%36.3%7.7%
       ≥ 30.0816.6%95.1%72.8%71.6%81.5%50.6%23.5%
      Exercise minutes/wk
       ≤301219.7%95.9%0.15772.7%0.13665.3%0.59074.4%0.01731.4%0.36012.4%0.004
       31 – 15038130.8%91.6%72.4%61.7%71.1%36.0%8.9%
       151 – 30036629.4%92.6%75.7%62.6%71.0%39.6%17.2%
       >30037830.3%89.7%68.0%59.0%62.7%35.2%10.6%
      Exercises with team
       Yes51341.1%90.8%0.33068.0%0.01060.2%0.48869.2%0.81340.2%0.02012.7%0.658
       No73558.9%92.4%74.7%62.2%68.6%33.7%11.8%
      Weight gain/lose
       Trying to lose weight54844.0%91.4%0.21474.1%<0.00162.8%0.00270.1%0.63937.8%0.63414.6%0.030
       Trying to gain weight1199.6%88.2%54.6%46.2%69.7%37.0%6.7%
       Maintaining weight57946.5%92.9%73.7%63.4%67.5%35.1%11.1%
      Tobacco use
       Never89371.6%91.8%0.63470.2%0.09362.2%0.32868.6%0.59933.0%<0.00110.5%0.018
       Former14911.9%89.9%75.8%63.1%66.4%43.6%16.8%
       Current20616.5%92.7%76.7%56.8%71.4%45.6%16.0%
      The bolded P values i identify them as statistically significant (P ≤ 0.05) values.
      a The total number of respondents with the given characteristic in the row, i.e. the denominator for all the percentages in that row.
      b The percent of respondents with the given characteristic in the row who indicated any consumption of caffeine from the source shown in the column i.e. row percents.
      c Pearson chi-square statistic for overall association between given row characteristic and any consumption of caffeine from the source shown in the column.
      More females than males reported using any caffeine (P < 0.001), coffee (P < 0.001) and tea (P < 0.001) (Table 1). Older (23 + years) students were less likely to drink tea (P = 0.002), while African-Americans were less likely to drink coffee (P < 0.001) (Table 1). Individuals trying to gain weight, were less likely to drink coffee (P < 0.001) or tea (P = 0.002), while obese respondents (BMI ≥ 30) were more likely to consume caffeine in tea (P = 0.001) (Table 1). Those reporting comparatively better general health were less likely to drink soda (P = 0.003) or energy drinks (P = 0.023) containing caffeine. Significantly fewer persons who exercised regularly with a team reported drinking coffee (68.0% vs. 74.7%, P = 0.01), however more reported drinking energy drinks (40.2% vs. 33.7%, P = 0.02) (Table 1). Non-smokers were less likely to drink energy drinks (P < 0.001) (Table 1).
      Mean daily caffeine intake for all students surveyed, including non-consumers, was 159 mg/d. The average intake (mg/d) of caffeine among self-reported caffeine consumers with respect to sociodemographic and lifestyle characteristics is shown in Table 2. Mean intake was 120 mg/d (males) and 111 mg/d (females) for coffee; 61 mg/d (males) and 50 mg/d (females) for tea; 38 mg/d (males) and 36 mg/d (females) for soda; 53 mg/d (males) and 30 mg/d (females) for energy drinks; and 25 mg/d (males) and 48 mg/d (females) for other (Table 2). Overall, no difference in amount of caffeine consumed from all sources was found between male and female college students (males: 173.9 mg/d; females: 173.4 mg/d; P = 0.61). However, males reported consuming significantly more caffeine from energy beverages than did females (males: 53.2 mg/d; females: 30.0 mg/d, P = 0.02). Older students (23 + years) consumed the most total caffeine 234.3 mg/d and caffeine from coffee 147.3 mg/d, tea 83.2 mg/d and energy drinks 81.8 mg/d (all P < 0.001) compared to other age groups. Those who reported poorer health consumed significantly more caffeine from all sources (P < 0.001) and specifically from sodas (P < 0.001) compared to those reporting better health status. Students currently using tobacco products had a higher intake of caffeine in general (P < 0.001), as well as coffee (P < 0.001), tea (P = 0.014), soda (P = 0.021) and energy drinks (P < 0.001) compared to non-smokers. As would be expected, those spending more on caffeine-containing products consumed more caffeine in general (P < 0.001), as well as coffee (P < 0.001), tea (P < 0.001), soda (P = 0.033) and energy drinks (P = 0.02) (Table 2). Students who reported never mixing energy drinks with alcohol consumed the least caffeine overall (P < 0.001) and the least caffeine from energy drinks (P = 0.04).
      Table 2Average consumption (mg/d) of caffeine, overall from all sources and for specific caffeine-containing products, according to selected sociodemographic characteristics and lifestyle factors, among consumers of caffeine and specific caffeine products.
      All caffeine (N = 1,145)Coffee (N = 898)Tea (N = 766)Soda (N = 859)Energy drinks (N = 454)Other
      Includes hot cocoa and other caffeine-containing milk products, as well as gum, candy or medication.
      (N = 152)
      Mean(SEM)P
      P-values are for an overall Type 3 F-statistic derived from ANOVA with consumption of the given type of caffeine-containing product (in mg) as the dependent variable and the characteristic in the first column as a categorical independent variable. The sample for each model includes only those with some consumption of the specified type of caffeine, and each model is adjusted only for survey location (College 1 – College 5).
      Mean(SEM)PMean(SEM)PMean(SEM)PMean(SEM)PMean(SEM)P
      Sex
       Male173.9(10.6)0.609120.3(9.4)0.35960.9(8.1)0.09138.3(3.0)0.43953.2(8.2)0.01824.8(7.3)0.305
       Female173.4(6.9)111.0(5.8)50.1(3.0)36.0(3.3)30.0(3.9)48.3(8.8)
      Age (years)
       18–19163.4(9.0)<0.001105.6(8.9)<0.00152.7(4.3)<0.00132.9(2.7)0.61030.2(5.8)0.00138.3(10.0)0.891
       20–22162.3(7.5)109.1(6.5)45.3(3.5)38.7(4.0)33.7(4.2)45.5(9.7)
       23+234.3(20.0)147.3(14.0)83.2(15.0)38.7(5.1)81.8(19.6)44.5(21.8)
      Race/ethnicity
       Non-hispanic white178.3(7.1)0.550122.3(6.1)0.11347.6(3.2)0.01137.7(3.1)0.75839.1(5.0)0.84245.9(9.1)0.625
       Non-hispanic black165.0(20.1)81.3(16.8)74.1(12.6)47.4(8.2)41.7(19.2)65.3(24.1)
       Hispanic/latino170.1(16.5)98.7(13.9)63.8(9.4)33.1(4.3)48.5(13.8)27.7(9.9)
       Asian144.1(18.3)93.4(16.5)44.9(8.6)28.8(6.4)34.3(9.0)20.5(12.2)
       Other177.6(30.0)96.6(19.7)87.3(30.5)27.0(5.3)26.7(6.4)10.4(3.9)
      Family income
       <$25K164.0(22.3)0.97681.5(13.7)0.01373.6(23.5)0.12241.9(7.4)0.07541.7(17.1)0.96824.1(11.6)0.746
       $25K – $99,999167.4(9.3)96.9(7.2)52.5(4.5)45.9(5.1)41.9(6.9)49.3(10.1)
       $100K – $200K177.0(10.6)132.1(10.6)44.6(4.2)32.5(3.5)34.3(5.3)33.1(10.8)
       >$200K186.2(19.0)134.0(15.7)61.2(10.7)27.8(3.3)27.6(10.0)53.0(39.2)
      General health
       Excellent150.1(8.5)0.001114.3(7.7)0.41347.2(5.7)0.21025.3(2.4)<0.00128.8(7.2)0.11621.0(6.2)0.209
       Good183.0(7.9)116.2(6.9)54.6(3.9)39.4(2.5)41.4(4.9)52.3(11.2)
       Fair/Poor214.0(25.2)89.1(12.5)71.2(12.6)67.1(23.1)60.2(19.1)52.9(13.6)
      Body mass index
       <18.5171.7(25.8)0.652117.9(25.7)0.57554.6(9.9)0.68239.6(8.9)0.34328.7(10.6)0.20310.4(2.5)0.535
       18.5–24.9171.0(6.9)116.4(6.0)50.9(3.9)33.9(2.2)34.6(4.6)43.5(9.3)
       25.0–29.9178.1(14.0)116.5(12.4)56.6(7.3)45.1(8.7)39.1(6.9)52.4(21.8)
       ≥ 30.0193.8(21.7)87.7(13.4)64.5(10.8)41.9(6.4)64.4(20.7)31.9(10.2)
      Weight gain/lose
       Trying to lose wt.187.2(9.2)0.050107.4(7.6)0.37761.5(5.5)0.06041.3(4.4)0.09142.5(6.3)0.11954.7(10.1)0.339
       Trying to gain wt.168.0(20.9)130.9(21.1)40.7(7.1)46.2(5.9)62.6(18.6)38.2(17.7)
       Maintain weight162.3(7.9)117.3(6.9)47.2(3.9)30.5(2.5)30.3(4.7)28.8(10.6)
      Exercise (min/wk)
       ≤30176.8(22.6)0.181123.9(21.0)0.32949.1(10.6)0.94140.9(6.8)0.21543.3(10.5)0.90227.2(10.4)0.792
       31–150173.2(9.6)106.6(7.8)56.0(6.6)40.1(3.4)42.0(7.7)37.0(9.1)
       151–300191.7(11.1)123.1(9.0)53.6(5.0)39.7(5.9)36.3(7.1)48.0(13.6)
       >300155.6(10.0)108.0(9.2)51.1(5.3)28.4(2.9)37.7(7.6)45.7(13.7)
      Exercises with team
       Yes155.6(8.5)0.119102.5(7.7)0.13154.1(5.7)0.89532.7(2.5)0.14337.3(5.6)0.65566.0(14.1)0.011
       No180.7(7.5)121.0(6.5)52.5(3.6)39.7(3.6)40.4(5.7)25.7(5.7)
      Tobacco use
       Never151.1(6.0)<0.001103.4(5.7)<0.00148.0(2.9)0.01433.5(3.0)0.02127.3(3.4)<0.00141.1(8.4)0.216
       Former203.5(18.8)120.3(12.8)58.2(13.7)34.5(3.9)66.2(18.0)19.1(5.7)
       Current249.0(17.9)150.6(13.8)73.4(10.6)52.1(5.1)56.9(9.9)66.0(21.1)
      Average monthly expenditure on caffeine products
       None108.8(12.4)<0.00157.8(9.7)<0.00154.9(7.6)<0.00146.1(14.1)0.03316.0(4.8)0.02071.2(29.4)0.410
       <$30/month114.5(7.2)73.8(6.0)39.0(3.6)26.8(2.9)29.1(6.6)26.1(8.1)
       $30–59/month197.7(10.2)119.7(8.6)45.0(4.0)40.7(3.4)50.2(8.3)49.8(11.5)
       $60–99/month268.9(23.3)166.9(20.0)76.8(14.2)43.4(6.0)34.3(7.3)27.9(8.7)
       ≥ $100/month297.7(24.4)194.1(18.7)95.2(17.0)47.2(5.7)47.5(13.6)44.8(25.4)
      % of Energy drinks with alcohol
       0% (none)176.0(11.4)<0.001108.5(10.5)0.18851.2(5.3)0.08738.1(3.6)0.59528.4(3.9)0.04030.8(7.6)0.825
       1%–24%228.7(15.9)125.2(11.9)56.8(6.5)39.7(4.1)57.1(9.9)54.5(17.4)
       25–49%239.9(31.7)154.0(28.2)27.3(4.0)53.6(15.0)44.1(10.1)49.9(28.2)
       50%–100%197.3(25.2)108.0(13.9)79.1(22.1)42.0(7.2)44.1(15.4)47.5(18.8)
       Does not consume energy drinks139.4(6.3)107.8(6.2)48.8(3.6)32.9(3.9)0NA44.5(13.6)
      The bolded P values identify them as statistically significant (P ≤ 0.05) values.
      a Includes hot cocoa and other caffeine-containing milk products, as well as gum, candy or medication.
      b P-values are for an overall Type 3 F-statistic derived from ANOVA with consumption of the given type of caffeine-containing product (in mg) as the dependent variable and the characteristic in the first column as a categorical independent variable. The sample for each model includes only those with some consumption of the specified type of caffeine, and each model is adjusted only for survey location (College 1 – College 5).
      Multiple linear regression models for caffeine overall intake from all sources and for specific products, with the sample for each model being those reporting any consumption of that product, are presented in Table 3. The coefficients estimate the difference in caffeine intake (mg/d) among caffeine users associated with each independent variable, holding other factors in the model constant. No significant difference was found in total caffeine consumption between males and females. Mean caffeine intake for older students (23 + years old) was about 95 mg/d more than for 18–19 year-olds (P < 0.001). Tobacco users consumed approximately 97 mg/d more caffeine than non-smokers (P < 0.001). Race/ethnicity, family income, general health and weight gain/loss were not independently associated with overall caffeine intake from all sources.
      Table 3Multiple linear regression models to examine the association of daily caffeine consumption (mg/day) with selected sociodemographic and lifestyle factors, among consumers of caffeine and specified caffeine products.
      All estimates are adjusted for the other variables shown in the table. Additionally, estimates are adjusted for site (college 1–5) and an indicator for those with unknown income.
      .
      VariableAll caffeine (N = 1130)Coffee (N = 887)Tea (N = 756)Soda (N = 846)Energy drinks (n = 449)
      Estimate
      All estimates are adjusted for the other variables shown in the table. Additionally, estimates are adjusted for site (college 1–5) and an indicator for those with unknown income.
      (SE)
      PEstimate (SE)PEstimate (SE)PEstimate (SE)PEstimate (SE)P
      Male gender−13.68 (13.27)0.303−10.11 (11.82)0.39312.23 (7.61)0.1082.44 (5.54)0.65910.25 (9.33)0.273
      Age (years)
       23+95.35 (18.97)<0.00162.99 (16.32)<0.00132.18 (10.64)0.0031.90 (7.97)0.81140.03 (13.81)0.004
       20 to 2210.26 (12.95)0.42812.64 (11.22)0.260−6.74 (7.05)0.3392.27 (5.44)0.676−3.21 (9.04)0.723
       18–19ReferenceReferenceReferenceReferenceReference
      Race/ethnicity
       Non-hispanic black−11.20 (23.20)0.629−30.91 (23.38)0.18629.25 (12.26)0.0173.23 (9.51)0.7343.54 (16.82)0.833
       Hispanic/latino9.26 (20.98)0.6590.59 (17.70)0.97317.12 (11.76)0.146−6.74 (8.83)0.44610.76 (15.24)0.481
       Asian−21.22 (21.41)0.322−28.85 (17.99)0.1092.48 (11.38)0.828−6.54 (9.20)0.477−2.98 (15.82)0.851
       Other1.08 (27.50)0.969−16.55 (23.16)0.47538.65 (14.33)0.007−13.77 (12.54)0.273−15.42 (16.74)0.358
       Non-hispanic whiteReferenceReferenceReferenceReferenceReference
      Family income
       $100,000 – $200,000−5.09 (21.29)0.8110.42 (18.38)0.982−20.17 (12.09)0.0962.83 (8.56)0.741−4.53 (14.93)0.762
       $25,000 – $99,999−10.66 (20.59)0.605−29.71 (17.71)0.094−13.69 (11.76)0.24515.13 (8.29)0.068−2.97 (14.55)0.838
       < $25,000−19.04 (28.31)0.501−43.77 (24.67)0.0764.29 (16.01)0.78911.87 (11.74)0.312−3.88 (19.26)0.840
       >$200,000ReferenceReferenceReferenceReferenceReference
      General health
       Fair/poor50.11 (25.59)0.051−9.83 (22.39)0.6616.74 (13.95)0.62937.64 (10.57)<0.00128.76 (17.90)0.109
       Good26.33 (12.79)0.04012.51 (11.15)0.2623.09 (7.15)0.66510.98 (5.47)0.0456.95 (9.54)0.467
       ExcellentReferenceReferenceReferenceReferenceReference
      Weight gain/lose
       Trying to lose wt.13.67 (12.69)0.282−5.70 (10.96)0.6039.80 (7.04)0.1644.36 (5.35)0.4158.49 (9.03)0.348
       Trying to gain wt.22.70 (21.75)0.29725.10 (20.41)0.219−16.97 (13.39)0.20612.62 (8.99)0.16123.56 (15.17)0.121
       Maintaining weightReferenceReferenceReferenceReferenceReference
      Tobacco use
       Current96.72 (16.01)<0.00152.92 (13.69)<0.00121.90 (9.21)0.01813.10 (6.68)0.05022.01 (10.51)0.037
       Former39.23 (18.19)0.03114.22 (15.33)0.3543.52 (9.88)0.722−2.80 (7.72)0.71726.79 (11.93)0.025
       NeverReferenceReferenceReferenceReferenceReference
      The bolded P values identify them as statistically significant (P ≤ 0.05) values.
      a All estimates are adjusted for the other variables shown in the table. Additionally, estimates are adjusted for site (college 1–5) and an indicator for those with unknown income.
      In columns 3–6 of Table 3 the results of regression models computed individually for the four major sources of caffeine intake in college students' diets: coffee, tea, soda and energy drinks are presented. Coffee consumption was higher among older students 23 + years old, who consumed an average of 63 mg/d more caffeine from coffee than younger students (P < 0.001) and among smokers, who consumed an average of 53 mg/d more than non-smokers (P < 0.01). Older age (P = 0.003) and current smoking (P = 0.018) were independently associated with greater intake of caffeine from tea. Those reporting fair/poor health (P < 0.001) and smokers (P = 0.050) consumed more caffeine from soda. Older students (P = 0.004), current smokers (P = 0.037) and former smokers (P = 0.025) consumed more caffeine from energy drinks than their younger, non-smoking counterparts.
      Table 4 provides the reasons college students reported they used caffeine. The most common cited were: to feel more awake (79%); enjoy the taste (68%); due to the social aspects of having coffee with friends or family (39%); to improve concentration (31%); to increase physical energy (27%); to improve mood (18%); and to alleviate stress (9%).
      Table 4Reasons for caffeine use, caffeine users only (N = 1145).
      Reason(s) for caffeine use
      Reasons are not mutually exclusive; therefore, percentages may add up to more than 100.
      Total N (%)
      To feel more awake and alert872 (78.5)
      Enjoy the taste752 (67.7)
      Social aspects434 (39.1)
      To improve concentration342 (30.8)
      Increase physical energy294 (26.5)
      To improve mood202 (18.2)
      Alleviate Stress102 (9.2)
      Other Reason(s)
      Other reasons given included “To get rid of headaches”, “Just happens to be in the drinks that I consume”, and “Morning ritual”.
      46 (4.1)
      To help lose weight34 (3.1)
      To improve creativity28 (2.5)
      a Reasons are not mutually exclusive; therefore, percentages may add up to more than 100.
      b Other reasons given included “To get rid of headaches”, “Just happens to be in the drinks that I consume”, and “Morning ritual”.

      4. Discussion

      The present study quantifies caffeine use by college undergraduates using data from a convenience sample of over 1200 students at five universities. It is based on a detailed survey that examined the quantity and frequency of consumption of a range of caffeinated products as well as sociodemographic and lifestyle factors of the volunteers. Over 90% of students reported consuming caffeine at least once in the past year, with the majority regularly consuming coffee, tea and soda. Total mean caffeine consumption per capita (for the whole student population surveyed) was 159 mg/d. Among regular caffeine users, total mean caffeine consumption from all reported sources was approximately 173 mg per day for both men and women. This is consistent with other recent estimates of caffeine intake of the U.S. population, although somewhat higher than individuals of the same age as the students we studied [
      • Fulgoni III, V.L.
      • Keast D.R.
      • Lieberman H.R.
      Trends in intake and sources of caffeine in the diets of U.S. Adults: 2001–2010.
      ,
      • Mitchell D.C.
      • Knight C.A.
      • Hockenberry J.
      • Teplansky R.
      • Hartman T.J.
      Beverage caffeine intakes in the U.S..
      ,
      • Tran N.L.
      • Barraj L.M.
      • Bi X.
      • Jack M.M.
      Trends and patterns of caffeine consumption among US teenagers and young adults, NHANES 2003–2012.
      ]. Individual caffeine intake varied considerably in this population as it does in the general population and was not normally distributed [
      • Fulgoni III, V.L.
      • Keast D.R.
      • Lieberman H.R.
      Trends in intake and sources of caffeine in the diets of U.S. Adults: 2001–2010.
      ,
      • Drewnowski A.
      • Rehm C.D.
      Sources of caffeine in diets of US children and adults: trends by beverage type and purchase location.
      ]. Total caffeine intake of U.S. college students who consume caffeine appears similar, but slightly higher, than the intake of Dutch students, who consume on average 144 mg/d, although direct comparison of these studies is not possible due to procedural differences [
      • Mackus M.
      • van de Loo A.J.A.E.
      • Benson S.
      • Scholey A.
      • Verster J.C.
      Consumption of caffeinated beverages and the awareness of their caffeine content among Dutch students.
      ].
      The demographic composition of students sampled in this study was quite similar to the U.S. college population [
      • National Center for Education Statistics
      Digest of education statistics 2015 NCES 2016-014.
      ]. Like the overall population of college students, more females than males were sampled in this survey. Our student sample was predominately white, like the general student population, although also like the overall population there were a number of blacks, Hispanics and Asian individuals in our sample. Overall, the size of the minority population sample who participated in this survey was approximately the same as the general student population. Our sample was also similar in age to the overall college population, with the largest group of students in our survey composed of those aged 24 or less, like the general college population.
      The current study is one of the first and largest to examine the relationship of caffeine intake from caffeine-containing products including energy drinks with a comprehensive set of demographic and lifestyle variables among U.S. college students. Like Dutch students [
      • Mackus M.
      • van de Loo A.J.A.E.
      • Benson S.
      • Scholey A.
      • Verster J.C.
      Consumption of caffeinated beverages and the awareness of their caffeine content among Dutch students.
      ], U.S. students surveyed consumed most of their caffeine from coffee (males = 120.3 mg/d, females = 111.0 mg/d) and tea (males = 60.9 mg/d; females = 50.1 mg/d). Student daily consumption of caffeine from energy beverages was 53.2 mg/d for males and 30.0 mg/d for females. Soda was a significant source of caffeine (38.3 mg/d for males and 36.0 mg/d for females). The aggregate mean intake of caffeine from all sources by college students was well within levels considered to be acceptable by U.S. government recommendations [

      U.S. Department of Health and Human Services. Dietary guidelines for Americans, 2015–2020. Accessed Nov. 26, 2016. Available online: https://health.gov/dietaryguidelines/2015/guidelines/.

      ]. However, like the general population, some students consume more caffeine (over 400 mg per day) than has been advised by some authors [

      U.S. Department of Health and Human Services. Dietary guidelines for Americans, 2015–2020. Accessed Nov. 26, 2016. Available online: https://health.gov/dietaryguidelines/2015/guidelines/.

      ,
      • Nawrot P.
      • Jordan S.
      • Eastwood J.
      • Rotstein J.
      • Hugenholtz A.
      • Feeley M.
      Effects of caffeine on human health.
      ,
      • Wikoff D.
      • Welsh B.T.
      • Henderson R.
      • Brorby G.P.
      • Britt J.
      • Myers E.
      • et al.
      Systematic review of the potential adverse effects of caffeine consumption in healthy adults, pregnant women, adolescents, and children.
      ]. Levels of safe or ‘optimal’ caffeine intake remain controversial, due to limited safety data and because research indicates consumption of caffeine may be beneficial both acutely and chronically [
      • Nawrot P.
      • Jordan S.
      • Eastwood J.
      • Rotstein J.
      • Hugenholtz A.
      • Feeley M.
      Effects of caffeine on human health.
      ,
      • Wikoff D.
      • Welsh B.T.
      • Henderson R.
      • Brorby G.P.
      • Britt J.
      • Myers E.
      • et al.
      Systematic review of the potential adverse effects of caffeine consumption in healthy adults, pregnant women, adolescents, and children.
      ,
      • Lieberman H.R.
      Nutrition, brain function and cognitive performance.
      ,
      • Haskell C.F.
      • Kennedy D.O.
      • Wesnes K.A.
      • Scholey A.B.
      Cognitive and mood improvements of caffeine in habitual consumers and habitual non-consumers of caffeine.
      ,
      • U.S. Department of Agriculture
      Scientific report of the 2015 dietary guidelines advisory Committee.
      ,
      • McLellan T.M.
      • Caldwell J.A.
      • Lieberman H.R.
      A review of caffeine's effects on cognitive, physical and occupational performance.
      ]. A recent comprehensive systematic review of possible adverse effects of caffeine in all forms on the cardiovascular system, bone status, reproductive health and development, as well as behavior concluded that, for adults, caffeine intake of up to 400 mg per day did not pose any risk [
      • Wikoff D.
      • Welsh B.T.
      • Henderson R.
      • Brorby G.P.
      • Britt J.
      • Myers E.
      • et al.
      Systematic review of the potential adverse effects of caffeine consumption in healthy adults, pregnant women, adolescents, and children.
      ]. Wikoff and colleagues also concluded that consumption of up to 2.5 mg/kg per day of caffeine was safe for adolescent populations [
      • Wikoff D.
      • Welsh B.T.
      • Henderson R.
      • Brorby G.P.
      • Britt J.
      • Myers E.
      • et al.
      Systematic review of the potential adverse effects of caffeine consumption in healthy adults, pregnant women, adolescents, and children.
      ].
      Energy drinks were first marketed in the U.S. in 1997, and recent data indicate annual energy drink and energy shot sales increased from approximately $8 billion in 2011 to over $13 billion in 2015 [
      • Statista
      U.S. Energy drinks industry and market - statistics & facts.
      ]. Common reasons reported by college students for seeking caffeine from energy drinks include increasing energy or counteracting insufficient sleep, to improve exercise performance and to study [
      • Attila S.
      • Cakir B.
      Energy-drink consumption in college students and associated factors.
      ,
      • Malinauskas B.M.
      • Aeby V.G.
      • Overton R.F.
      • Carpenter-Aeby T.
      • Barber-Heidal K.
      A survey of energy drink consumption patterns among college students.
      ]. However, in this study we assessed reasons for use of caffeine in general not energy drinks alone. Several recent papers have addressed the safety of energy drinks and raised concerns regarding excessive consumption of these products by adolescents and adults [
      • Lippi G.
      • Cervellin G.
      • Sanchis-Gomar F.
      Energy drinks and myocardial ischemia: a review of Case reports.
      ,
      • Sanchis-Gomar F.
      • Pareja-Galeano H.
      • Cervellin G.
      • Lippi G.
      • Earnest C.P.
      Energy drink overconsumption in adolescents: implications for arrhythmias and other cardiovascular events.
      ].
      Although the age range in the present sample was small, caffeine use significantly increased with age, consistent with reports that caffeine consumption is greatest amongst individuals 45–60 years of age [
      • Tran N.L.
      • Barraj L.M.
      • Bi X.
      • Jack M.M.
      Trends and patterns of caffeine consumption among US teenagers and young adults, NHANES 2003–2012.
      ]. In this study, women consumed more caffeine from ‘other’ products such as cocoa than men, while men consumed more caffeine from energy drinks, coffee and tea. Despite gender differences in consumption of these sources of caffeine, men and women did not differ in total daily caffeine intake. Norton and colleagues [
      • Norton T.R.
      • Lazev A.B.
      • Sullivan M.J.
      The “buzz” on caffeine: patterns of caffeine use in a convenience sample of college students.
      ] also did not find gender difference in caffeine consumption among college students.
      Smokers reported consuming more caffeine in general, as well as coffee, soda and energy drinks than non-smokers. Higher caffeine intake among smokers than non-smokers is well-documented [
      • Brice C.F.
      • Smith A.P.
      Factors associated with caffeine consumption.
      ,
      • Hewlett P.
      • Smith A.
      Correlates of daily caffeine consumption.
      ,
      • McPhillips J.B.
      • Eaton C.B.
      • Gans K.M.
      • Derby C.A.
      • Lasater T.M.
      • McKenney J.L.
      • et al.
      Dietary differences in smokers and nonsmokers from two southeastern New England communities.
      ]. Physiological, cognitive and environmental factors all may contribute to the association between smoking and caffeine intake. Nicotine use increases the rate of caffeine metabolism; as a consequence, smokers must consume caffeine more frequently than non-smokers to maintain the same internal (e.g. plasma) levels. Other factors, such as stress, could have similar effects on use of both caffeine and nicotine leading to increased use of both [
      • Swanson J.A.
      • Lee J.W.
      • Hopp J.W.
      Caffeine and nicotine: a review of their joint use and possible interactive effects in tobacco withdrawal.
      ].
      A variety of other factors may also be associated with caffeine intake. For example, in the general population race is strongly associated with overall caffeine intake, with non-Hispanic Whites consuming the most caffeine and non-Hispanic Blacks consuming the least [
      • Fulgoni III, V.L.
      • Keast D.R.
      • Lieberman H.R.
      Trends in intake and sources of caffeine in the diets of U.S. Adults: 2001–2010.
      ,
      • Drewnowski A.
      • Rehm C.D.
      Sources of caffeine in diets of US children and adults: trends by beverage type and purchase location.
      ,
      • Branum A.M.
      • Rossen L.M.
      • Schoendorf K.C.
      Trends in caffeine intake among US children and adolescents.
      ]. Among the college students we studied non-Hispanic Blacks did consume less caffeine than whites but the difference was smaller than is observed in the general population and not statistically significant.
      Limited data are available on the reasons individuals choose to use caffeine-containing products. Among the college students we surveyed, many reported using caffeine-containing products to enhance some aspect of mood or performance such as to feel more awake (79%), improve concentration (31%), increase physical energy (27%), improve mood (18%) and alleviate stress (9%). Numerous research studies assessing cognitive performance, physical performance and mood after caffeine administration corroborate these self-reported observations [
      • Barone J.J.
      • Roberts H.R.
      Caffeine consumption.
      ,
      • Amendola C.A.
      • Gabrieli J.D.E.
      • Lieberman H.R.
      Caffeine's effects on performance and mood are independent of age and gender.
      ,
      • Bordeaux B.
      • Lieberman H.R.
      Benefits and risks of caffeine and caffeinated beverages.
      ]. Jeffers et al. [
      • Jeffers A.J.
      • Vatalaro Hill K.E.
      • Benotsch E.G.
      Energy drinks, weight loss, and disordered eating behaviors.
      ] reported that energy drink users were more likely to be attempting to lose weight. However, we found that aggregate use of caffeine was significantly associated with weight loss but not specifically energy drink use.
      There are some limitations to this study. Self-reported data are always subject to various types of biases, such as recall bias. In addition, this study was limited to five colleges, although previous studies typically only survey one [
      • Attila S.
      • Cakir B.
      Energy-drink consumption in college students and associated factors.
      ]. The survey is based on a convenience sample that, while similar, was not representative of the U.S. college population. It should also be noted that due to the methods used to recruit volunteers it was not possible to calculate response rate.

      5. Conclusions

      Among all the college undergraduates surveyed, per capita caffeine consumption averaged 159 mg/d and was 173 mg/d for individuals who were regular users of caffeine. Most consumers of caffeine-containing products reported using them to enhance mood and performance. Most caffeine was consumed in the form of coffee and tea, not energy drinks. Thirty-six percent of students reported consuming energy drinks, with non-smokers, women and individuals who perceive themselves to be in better health consuming fewer energy drinks than smokers, men and those perceiving themselves to be in poorer health.

      Conflict of interest

      None.

      Acknowledgements

      The views, opinions and findings in this report are those of the authors and should not be construed as an official Department of Defense policy, or decision, unless so designated by other official documentation. Citations of commercial organizations and trade names in this report do not constitute an official Department of the Army endorsement or approval of the products or services of these organizations. The investigators have adhered to the policies for protection of human subjects as prescribed in DOD Instruction 3216.02 and the project was conducted in adherence with the provisions of 32 CFR Part 219. This work was supported by the Defense Medical Research and Development Program (DMRDP) and US Army Medical Research and Materiel Command (USAMRMC). The authors have no conflicts of interest to declare.

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