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HTN: Caffeine (2007)

Citation:
 
Study Design:
Class:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:

To quantify the chronic effect (seven days) of regular coffee and caffeine intake on blood pressure, using data from randomized controlled trials.

Inclusion Criteria:
  • Conducted in humans
  • Random allocation of study participants to intervention and control groups.
Exclusion Criteria:
  • Duration of intervention of less than seven days
  • Duplicate publication of the same study
  • Co-intervention with ephedrine, nicotine or stress from which the effect of coffee or caffeine could not be separated
  • Lack of concurrent control group or balanced crossover comparison period
  • Lack of data to calculate net changes in blood pressure.
Description of Study Protocol:
  • Recruitment: Blood pressure trials of coffee or caffeine published between January 1966 and January 2003 were identified through literature databases (Medline, Embase, Lilacs and Current Contents) using terms of 'coffee or caffeine,' 'blood pressure or hypertension' and 'trial or intervention or random or study' and manual search
  • Design: Meta-analysis
  • Blinding used: Not applicable.
  • Intervention: Two people independently obtained data on sample size, type and duration of intervention, changes in blood pressure and heart rate and subjects' characteristics for each trial. In case of disagreement, consensus was reached.

Statistical Analysis

  • Homogeneity of effect size across trials was tested by Q-statistics
  • Meta-analysis was performed using random-effects model. To calculate pooled effect size, each study weighed by reciprocal of variance of blood pressure change.
  • Heterogeneity in blood pressure response was examined by performing stratified meta-analyses
  • Funnel graphs were constructed in which blood pressure effects were plotted against weight factors to detect potential publication bias.
Data Collection Summary:
  • Timing of measurements: Effect of coffee or caffeine on blood pressure
  • Dependent variables: Blood pressure.

Independent Variables

  • Coffee or caffeine intake for at least seven days
  • Assumption of 150ml cup of coffee contains 90mg caffeine if not reported.
Description of Actual Data Sample:
  • Initial N: 91 out of 156 reports met initial criteria, but only 16 RCTS were eligible after application of exclusion criteria
  • Attrition (final N): 16 RCTs, comprising 25 strata and 1,010 subjects
  • Age: Mean ages between 23 and 77 years
  • Ethnicity: Not mentioned
  • Location: Worldwide studies.
Summary of Results:

Other Findings

  • Daily coffee dose varied from 450ml to 1,235ml per day, corresponding to a caffeine dose of 225mg to 798mg per day
  • Daily caffeine dose ranged from 295mg to 750mg per day
  • In coffee and caffeine trials combined, the median dose was 410mg per day
  • A significant rise of 2.04mmHg (95% CI: 1.10-2.99) in systolic blood pressure and 0.73mmHg (95% CI: 0.14-1.31) in diastolic blood pressure was found after pooling of coffee and caffeine trials
  • When coffee trials (N=18, median intake: 725ml per day) and caffeine trials (N=7, median dose: 410mg per day) were analyzed separately. Blood pressure elevations appeared to be larger for caffeine [systolic: 4.16mmHg (95% CI: 2.13-6.20); diastolic: 2.41mmHg (95% CI: 0.98-3.84)] than for coffee [systolic: 1.22mmHg (95% CI: 0.52-1.92); diastolic: 0.49 (95% CI: -0.06 to 1.04)].
  • Effects on heart rate were negligible.
Author Conclusion:
  • This meta-analysis shows that regular caffeine intake increaes blood pressure, although the pressure effect of caffeine was only small if ingested through coffee
  • More research is needed on the cardiovascular effects of caffeine and caffeinated foods and beverages other than coffee, such as cola and sport drinks.
Funding Source:
University/Hospital: Wageningen University
Reviewer Comments:

Well done statistical analysis.

Quality Criteria Checklist: Review Articles
Relevance Questions
  1. Will the answer if true, have a direct bearing on the health of patients? Yes
  2. Is the outcome or topic something that patients/clients/population groups would care about? Yes
  3. Is the problem addressed in the review one that is relevant to dietetics practice? Yes
  4. Will the information, if true, require a change in practice? Yes
 
Validity Questions
  1. Was the question for the review clearly focused and appropriate? Yes
  2. Was the search strategy used to locate relevant studies comprehensive? Were the databases searched and the search termsused described? Yes
  3. Were explicit methods used to select studies to include in the review? Were inclusion/exclusion criteria specified andappropriate? Wereselectionmethods unbiased? Yes
  4. Was there an appraisal of the quality and validity of studies included in the review? Were appraisal methodsspecified,appropriate, andreproducible? Yes
  5. Were specific treatments/interventions/exposures described? Were treatments similar enough to be combined? Yes
  6. Was the outcome of interest clearly indicated? Were other potential harms and benefits considered? Yes
  7. Were processes for data abstraction, synthesis, and analysis described? Were they applied consistently acrossstudies and groups? Was thereappropriate use of qualitative and/or quantitative synthesis? Was variation in findings among studies analyzed? Were heterogeneity issued considered? If data from studies were aggregated for meta-analysis, was the procedure described? Yes
  8. Are the results clearly presented in narrative and/or quantitative terms? If summary statistics are used, are levels ofsignificance and/or confidence intervals included? Yes
  9. Are conclusions supported by results with biases and limitations taken into consideration? Are limitations ofthe review identified anddiscussed? Yes
  10. Was bias due to the review's funding or sponsorship unlikely? Yes