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Hydration

HYD: Effect of Caffeinated Beverages on Fluids (2007)

Citation:
Frary CD, Johnson RK, Wang MQ. Food Sources and Intakes of Caffeine in the Diets of Persons in the United States. Journal of the American Dietetic Association. 2005; 105: 110-113. PubMed ID: 15635355
 
Study Design:
Cross-Sectional Study
Class:
D - Click here for explanation of classification scheme.
Quality Rating:
Positive POSITIVE: See Quality Criteria Checklist below.
Research Purpose:
To examine the caffeine intakes and food and beverage sources of caffeine in a representative sample of the U.S. population.
Inclusion Criteria:
  • Individuals who participated in the USDA Continuing Survey of Food Intakes by Individuals (CSFII) 1994-1996 and 1998 surveys and provided two full days of dietary intake data
  • Individuals who consumed sources of caffeine.
Exclusion Criteria:
  • Individuals with incomplete dietary intake data
  • Individuals who did not consume caffeine.
Description of Study Protocol:

Recruitment

Data was from the CSFII 1994-96 and 1998 data sets. CSFII 1994-96 resulted in a nationally representative sample of persons in the United States of all ages. CSFII 1998 resulted in a nationally representative sample of US children from birth to age nine years.

Design

Methods for sample selection, data collection, data file preparation and weighting were consistent in both surveys, so the data sets were combined.

  • The percentage of caffeine consumers in the total sample and by age and sex group and pregnant women were determined. Then mean intakes of caffeine (milligrams and milligrams per kilogram) were calculated.
  • Using the USDA Food Coding Scheme, caffeine-containing foods and beverages were classified into six categories: flavored dairy products,  sweetened grains, sugars and sweets, coffees, teas and soft drinks.
  • Mean intakes of caffeine (milligrams) by food and beverage category and the percent contribution to total caffeine intake were calculated.

Blinding used (if applicable)

Secondary examination of a published data set.

Statistical Analysis

The Statistical Export and Tabulation System (version 2.0, 1999, National Center for Health Statistics, Hyattsville, MD) was used to translate the CSFII data into a usable format.

  • The Statistical Analysis System (SAS 8.0, 1999, SAS Institute Inc, Cary, NC) was employed to recode and  format the data for statistical analysis
  • The Survey Data Analysis System (release 8.0.0, 2001, Research Triangle Institute, Research Triangle Park, NC) was used to weight the sample, compute variances and run the statistical procedures 
  • Weighting was conducted using USDA standard procedures for national surveys
  • The variance was computed using Taylor series linearization. Due to the large sample size, variability (standard error of the mean) was small and hence these data are not presented
  • The data were normally distributed.
Data Collection Summary:
  • Timing of Measurements: The CSFII survey years were identified, but beyond that measurement timing was not described.  See papers on CSFII methodology.
  • Dependent Variables: Dietary intake data.
  • Independent Variables: Caffeine-containing beverages and foods.
Description of Actual Data Sample:
  • Initial N: 18,081 individuals with complete two-day dietary intake data
  • Attrition (Final N): 15,716=caffeine consumers; only 15,201 provided body weights, therefore the N used for mg per kg per day calculations varied from the N used for mg per day (See Table 1 below)
  • Age: two to 65+ years
  • Ethnicity and Anthropometrics: Were not described
  • Other relevant demographics: Pregnant women who consumed caffeine were included; N=43
  • Location: The CSFII surveys were conducted nationwide.
Summary of Results:
  • 87% of the US population—nearly 90% of adults and male teens and 76% or more of children—consumed caffeine (Table 1)
  • The mean intake for all caffeine consumers was 193 mg per day and 1.2 mg per kg per day, with men age 35 to 54 years having the highest intakes, 336 mg per day and 1.7 mg per kg per day (Table 1)
  • Among persons ages two to 54 years, as age increased, caffeine consumption increased. Men and women age 35 to 64 years were among the highest consumers of caffeine (Table 1).
  • 68% of pregnant women consumed caffeine, with an average intake of 125 mg per day (Table 1)
  • Among caffeine consumers, coffee (71%), soft drinks (16%), and tea (12%) were the three top sources of caffeine (Table 2)
  • Coffee was the major source of caffeine in the diets of men and women older than age 18 years and pregnant women, whereas soft drinks were the major source for children age two to 17 years, providing 50% to 64% of caffeine (Table 2)
  • As children got older, intakes of caffeine from soft drinks, coffee and tea increased (Table 2).

Table 1: Mean caffeine intakes (milligrams and milligrams per kg of body weight) for U.S. caffeine consumers age two years and older by age-sex groups and pregnant women. Caffeine intakes based on a two-day average from Continuing Survey of Food Intakes by Individuals (CSFII) 1994-96 and 1998a

Age-sex

Sample of caffeine consumersb

% consuming caffeinec

mg/d

nc

mg/kg/d

Caffeine consumers

15,716

87

193

15,201

1.2

Children 2-5 y

4,116

76

16

3,869

0.4

Children 6-11 y

1,649

86

26

  1,553

0.4

Females 12-17 y

     493

88

59

     481

0.5

Males 12-17 y

     512

91

80

     505

0.6

Females 18-34 y

  1,073

89

166

  1,055

1.2

Males 18-34 y

  1,135

91

199

  1,130

1.1

Females 35-54 y

  1,590

94

250

  1,526

1.7

Males 35-54 y

  1,657

95

336

  1,645

1.8

Females 55-64 y

     728

95

228

     704

1.5

Males 55-64 y

     748

96

318

     746

1.8

Females 65+ y

     964

92

188

     941

1.3

Males 65+ y

  1,051

94

217

  1,046

1.3

Pregnant women

       43

68

125

       42

0.8

 a Estimates for persons age nine and younger based on combined data from CSFII 1994-96 and 1998; for persons aged 10 years and older, mean estimates based on data from CSFII 1994-96.

Sample size weighted.

c Sample size is different due to weights not reported in CSFII.

 

Table 2. Mean two-day caffeine intakes (mg) and the percent contribution of each food and beverage category to caffeine intake for all U.S. caffeine consumers age w 2 years and older (n=15,716) and pregnant women (n=43)                                                                            

Food and beverage category

Caffeine sample (n=15,716)

Child 2-5  (n=4,116)

Child 6-11 (n=1,649)

   Female    12-17  (n=493)

     Male       12-17  (n=512)

Male 18-34  (n=1,135)

Male 35-54  (n=1,657)

Mean(mg)a

%b

Mean

%

Mean

%

Mean

%

Mean

%

Mean

%

Mean

%

Flavored dairy products (chocolate and coffee-flavored milk, yogurt, ice cream)

0.7

0.4

1.0

6.2

1.7

6.4

0.9

1.5

1.7

2.1

0.5

0.2

0.5

0.2

Sweetened grains (chocolate-flavored pie, cake, cookie,brownie, doughnut, granola and breakfast bars, muffin, cereal)

0.9

0.5

1.1

7.1

1.5

5.7

1.2

2.0

1.5

1.8

1.0

0.5

1.1

0.3

Sugars and sweets (chocolate candy, topping, syrup, and icing, chocolate covered fruit)

0.8

0.4

0.7

4.4

1.0

3.7

0.9

1.5

1.1

1.4

0.8

0.4

0.9

0.3

Coffees (regular, espresso, latte, mocha, cappuccino)

136.4

70.7

0.3

2.1

1.1

4.2

3.5

5.9

7.9

9.8

111.5

56.1

260.9

77.6

Teas (leaf, instant)

23.4

12.1

4.8

30.0

6.1

23.6

16.1

27.3

16.7

20.9

 25.6

12.9

35.4

10.5

 

Soft drinks (cola-type, pepper-type,chocolate flavored, fruit flavored with caffeine)

30.6

15.9

 8.0

50.3

14.7

56.4

36.5

61.9

51.3

64.0

59.4

29.8

37.5

11.2

 

Food and beverage category

Male 55-64  (n=748)

Male 65+

(n=1,051)

   Female     18-34  (n=1,073)

   Female    35-54 (n=1,590)

  Female    55-64  (n=728)

Female 65+ (n=964)

Pregnant women

(n=43)

Mean(mg)a

%b

Mean

%

Mean

%

Mean

%

Mean

%

Mean

%

Mean

%

Flavored dairy products (chocolate and coffee-flavored milk, yogurt, ice cream)

0.3

0.1

0.6

0.3

0.6

0.3

0.4

0.2

0.4

0.2

0.3

0.2

1.0

0.8

Sweetened grains (chocolate-flavored pie, cake, cookie,brownie, doughnut, granola and breakfast bars, muffin, cereal)

0.8

0.3

0.8

0.4

0.8

0.5

0.7

0.3

0.6

0.3

0.6

0.3

0.9

0.7

Sugars and sweets (chocolate candy, topping, syrup, and icing, chocolate covered fruit)

0.6

0.2

0.5

0.2

0.8

0.5

0.7

0.3

0.6

0.3

0.4

0.2

2.3

1.9

Coffees (regular, espresso, latte, mocha, cappuccino)

271.0

85.2

182.2

84.1

101.2

61.1

190.9

76.4

185.5

81.3

154.6

82.2

59.3

 47.6

Teas (leaf, instant)

24.9

7.8

22.7

10.5

22.9

13.8

29.1

11.7

24.7

10.8

25.3

13.5

28.5

 22.9

 

Soft drinks (cola-type, pepper-type,chocolate flavored, fruit flavored with caffeine)

20.3

6.4

9.9

4.6

39.1

23.6

27.9

11.2

16.2

7.1

6.8

3.6

32.6

 26.2

 a Estimates for persons age nine and younger based on combined data from the Continuing Survey of Food Intakes by Individuals (CSFII) 1994-96 and 1998; for persons aged 10 years and older, mean estimates based on data from CSFII 1994-96.

Sample size weighted.

Author Conclusion:

The study findings suggest that during the past two decades, there is a higher percentage of persons in the United States at all ages who consume caffeine, while mean caffeine intakes may have decreased.

Shifts in the major sources of caffeine have occurred and are likely a result of changes in beverage consumption patterns.

Coffee remains the primary source of caffeine in the diets of persons in the United States. However, consumption of caffeine from soft drinks now exceeds the consumption of caffeine from tea.

The shift in the food and beverage sources of caffeine is likely associated with the increase in children’s consumption of soft drinks during the past two decades. 

The CSFII database did not include the caffeine intakes from energy beverages, herbals or medications.  This limitation, in addition to the pervasive problem of underreporting of food and beverage intakes in self-reported dietary intake surveys, may mean that caffeine intakes of persons in the United States were underestimated. 
Funding Source:
Reviewer Comments:
Quality Criteria Checklist: Primary Research
Relevance Questions
  1. Would implementing the studied intervention or procedure (if found successful) result in improved outcomes for the patients/clients/population group? (Not Applicable for some epidemiological studies) Yes
  2. Did the authors study an outcome (dependent variable) or topic that the patients/clients/population group would care about? Yes
  3. Is the focus of the intervention or procedure (independent variable) or topic of study a common issue of concern to dieteticspractice? Yes
  4. Is the intervention or procedure feasible? (NA for some epidemiological studies) Yes
 
Validity Questions
1. Was the research question clearly stated? Yes
  1.1. Was (were) the specific intervention(s) or procedure(s) [independent variable(s)] identified? Yes
  1.2. Was (were) the outcome(s) [dependent variable(s)] clearly indicated? Yes
  1.3. Were the target population and setting specified? Yes
2. Was the selection of study subjects/patients free from bias? Yes
  2.1. Were inclusion/exclusion criteria specified (e.g., risk, point in disease progression, diagnostic or prognosis criteria), and with sufficient detail and without omitting criteria critical to the study? Yes
  2.2. Were criteria applied equally to all study groups? Yes
  2.3. Were health, demographics, and other characteristics of subjects described? No
  2.4. Were the subjects/patients a representative sample of the relevant population? Yes
3. Were study groups comparable? Yes
  3.1. Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) Yes
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? N/A
  3.3. Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.) N/A
  3.4. If cohort study or cross-sectional study, were groups comparable on important confounding factors and/or were preexisting differences accounted for by using appropriate adjustments in statistical analysis? Yes
  3.5. If case control study, were potential confounding factors comparable for cases and controls? (If case series or trial with subjects serving as own control, this criterion is not applicable.) Yes
  3.6. If diagnostic test, was there an independent blind comparison with an appropriate reference standard (e.g., "gold standard")? N/A
4. Was method of handling withdrawals described? N/A
  4.1. Were follow-up methods described and the same for all groups? N/A
  4.2. Was the number, characteristics of withdrawals (i.e., dropouts, lost to follow up, attrition rate) and/or response rate (cross-sectional studies) described for each group? (Follow up goal for a strong study is 80%.) N/A
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? N/A
  4.4. Were reasons for withdrawals similar across groups? N/A
  4.5. If diagnostic test, was decision to perform reference test not dependent on results of test under study? N/A
5. Was blinding used to prevent introduction of bias? Yes
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? N/A
  5.2. Were data collectors blinded for outcomes assessment? (If outcome is measured using an objective test, such as a lab value, this criterion is assumed to be met.) Yes
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? Yes
  5.4. In case control study, was case definition explicit and case ascertainment not influenced by exposure status? N/A
  5.5. In diagnostic study, were test results blinded to patient history and other test results? N/A
6. Were intervention/therapeutic regimens/exposure factor or procedure and any comparison(s) described in detail? Were interveningfactors described? Yes
  6.1. In RCT or other intervention trial, were protocols described for all regimens studied? N/A
  6.2. In observational study, were interventions, study settings, and clinicians/provider described? Yes
  6.3. Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect? Yes
  6.4. Was the amount of exposure and, if relevant, subject/patient compliance measured? Yes
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described? N/A
  6.6. Were extra or unplanned treatments described? N/A
  6.7. Was the information for 6.4, 6.5, and 6.6 assessed the same way for all groups? Yes
  6.8. In diagnostic study, were details of test administration and replication sufficient? N/A
7. Were outcomes clearly defined and the measurements valid and reliable? Yes
  7.1. Were primary and secondary endpoints described and relevant to the question? Yes
  7.2. Were nutrition measures appropriate to question and outcomes of concern? Yes
  7.3. Was the period of follow-up long enough for important outcome(s) to occur? Yes
  7.4. Were the observations and measurements based on standard, valid, and reliable data collection instruments/tests/procedures? Yes
  7.5. Was the measurement of effect at an appropriate level of precision? Yes
  7.6. Were other factors accounted for (measured) that could affect outcomes? Yes
  7.7. Were the measurements conducted consistently across groups? Yes
8. Was the statistical analysis appropriate for the study design and type of outcome indicators? Yes
  8.1. Were statistical analyses adequately described and the results reported appropriately? Yes
  8.2. Were correct statistical tests used and assumptions of test not violated? Yes
  8.3. Were statistics reported with levels of significance and/or confidence intervals? Yes
  8.4. Was "intent to treat" analysis of outcomes done (and as appropriate, was there an analysis of outcomes for those maximally exposed or a dose-response analysis)? N/A
  8.5. Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)? Yes
  8.6. Was clinical significance as well as statistical significance reported? Yes
  8.7. If negative findings, was a power calculation reported to address type 2 error? N/A
9. Are conclusions supported by results with biases and limitations taken into consideration? Yes
  9.1. Is there a discussion of findings? Yes
  9.2. Are biases and study limitations identified and discussed? Yes
10. Is bias due to study's funding or sponsorship unlikely? Yes
  10.1. Were sources of funding and investigators' affiliations described? Yes
  10.2. Was the study free from apparent conflict of interest? Yes