HTN: Caffeine (2007)

Citation:
 
Study Design:
Class:
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Quality Rating:
Research Purpose:
To compare the acute effects of caffeine on arterial blood pressure in five hypertension risk groups.
Inclusion Criteria:
  • Men, fitting criteria for one of five hypertension risk groups, as defined by the Sixth Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure (JNC VI):
  1. Optimal, systolic blood pressure (SBP) under 120mm Hg and diastolic blood pressure (DBP) under 80mm Hg
  2. Normal, SBP 120mm to 129mm Hg or DBP 80mm to 84mm Hg
  3. High-normal, SBP 130mm to 139mm Hg or DBP 85mm to 89mm Hg
  4. Stage One, SBP 140mm to 159mm Hg or DBP 90mm to 99mm Hg
  5. Diagnosed hypertension, recruited from a hypertension clinic.
  • All subjects were in otherwise good health on the basis of physical examination and medical history
  • Among diagnosed hypertensives, seven men were taking ACE inhibitors, two were taking beta-blockers and two were taking hydrochlorathiazide
  • All hypertensive medications were tapered accordingly before the BP screening.
Exclusion Criteria:

None specified.

Description of Study Protocol:
  • Recruitment: Not specified other than risk group five was recruited from a hypertension clinic
  • Design: Meta-analysis of four randomized controlled crossover trials    
  • Blinding used: Four studies were double-blind.

Intervention

  • In all original studies, subjects were directed to abstain from caffeine after supper on the evening before coming to the laboratory, a period of 12 hours or more
  • In three of the studies, volunteers consumed unsweetened grapefruit juice mixed with 3.3mg per kg caffeine or they drank grapefruit juice alone (placebo)
  • In the fourth study, subjects took a caffeine-containing capsule (250mg plus lactose) or a placebo (lactose)
  • The 3.3mg per kg dose resulted in a mean dose of 260mg
  • Caffeine administration was followed by 45 to 60 minutes of absorption and post-caffeine BP readings were taken. 

Statistical Analysis

  • One-way ANOVA was used to compare the following variables of the risk groups: Age, height, weight, BMI, reported chronic caffeine intake, screening BPs and pre-drug baseline BPs
  • Pre- to post-drug caffeine effects on BP were examined with paired samples T-tests for each group. Pre-drug baseline BPs were examined with MANOVA with hypertension status as between-subject factors and SBP and DBP as dependent variables. 
  • The main analysis of between-subject effects was done with ANCOVA with post-caffeine BPs as dependent variables and baseline BPs as covariates, since group pre-drug BPs differed significantly
  • Hierarchical mutliple regression analyses with change scores (pre-caffeine and post-caffeine BPs) as dependent variables and risk group, BMI and age as independent variables.
Data Collection Summary:
  • Timing of measurements: Screening BP, pre-drug BP, then post-drug BP 45 to 60 minutes after caffeine administration
  • Dependent variables: SBP and DBP were measured with a BP cuff after semisupine rest for 20 minutes using a Dinamap Vital Signs Monitor (model 1896) or a Paramed monitor
  • Independent variables: A single caffeine dose of either 3.3mg per kg or 250mg.
Description of Actual Data Sample:
  • Initial N: 182 men whose data existed in the researcher database from four previous studies. 73 men had optimal BP, 28 had normal BP, 36 with high-normal BP, 27 with stage I HTN and 18 with diagnosed HTN.
  • Attrition (final N): Not discussed; would need to read any publications on each of the individual four studies
  • Mean Age
    • Optimal BP group: 29
    • Normal BP group: 26
    • High-normal BP group: 26
    • Stage I group: 27
    • Hypertension group: 39.
  • Ethnicity: Not specified
  • Other relevant demographics: None provided
  • Anthropometrics: Weight and BMI were significantly different between the risk groups
  • Location: Not specified for any of the studies from which the data were obtained.
Summary of Results:

Other Findings

  • Caffeine raised both SBP and DBP (P<0.0001) in all groups with large (at least 0.92) effect sizes, with the exception of pre- to post-SBP and DBP in the optimal group (medium effect sizes of 0.72 and 0.77, respectively)
  • The largest BP response to caffeine occurred in diagnosed hypertensive men, followed by stage I and high-normal groups and then by optimal and normal groups
  • After caffeine ingestion, 19% of the high-normal, 15% of the stage I and 89% of the diagnosed HTN groups fell into the hypertensive range
  • All subjects from the optimal and normal groups remained normo-tensive
  • HTN group status was the best predictor of SBP responsivity (R=0.24, P<0.001) and DBP responsivity (R=0.23, P<0.002).
Author Conclusion:
  • Progressively larger BP responses to caffeine occurred in persons with increasing risk of hypertension
  • Hypertension risk status should take priority in future research regarding pressor effects of dietary intake of caffeine.
Funding Source:
Government: Dept. of Veterans Affairs, NHLBI, oklahoma center for science and technology
Reviewer Comments:
  • The data were from men only and from more than one study, with some variation between protocols, including exact doses of caffeine
  • Participants were relatively young, compared to the relevant population the results would be applied to
  • Reports on caffeine abstinence prior to the study protocol were not available for over half of the participants
  • Furthermore, in all studies from which the data were obtained, the caffeine was administered with grapefruit juice
  • There is some evidence that grapefruit juice may inhibit the metabolism of caffeine, which could then potentiate the effects of caffeine due to slower clearance.
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? N/A
  3. Were explicit methods used to select studies to include in the review? Were inclusion/exclusion criteria specified andappropriate? Wereselectionmethods unbiased? No
  4. Was there an appraisal of the quality and validity of studies included in the review? Were appraisal methodsspecified,appropriate, andreproducible? ???
  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