EAL

HTN: Caffeine (2007)

Citation:

Study Design:

Class:

- Click here for explanation of classification scheme.

Quality Rating:

Research Purpose:

To investigate the effects of caffeine on blood pressure and platelet aggregation using the handgrip pressor test as a standard stimulus for the sympathetic system.

Inclusion Criteria:

Clinically healthy, with no addictions and no medication use
Men and women aged 21 to 27 years.

Exclusion Criteria:

Not specified.

Description of Study Protocol:

Recruitment: Not specified
Design: Non-randomized, non-placebo controlled trial
Intervention: All subjects abstained from caffeine-containing for seven days, followed by seven days of daily intake of 750mg of caffeine (divided into three 250-mg doses) and then followed by seven days of abstinence from caffeine
Statistical analysis: ANOVA, P<0.05 considered statistically significant.

Data Collection Summary:

Timing of Measurements

Data were collected on the eighth day (basal), 10th and 16th days (acute phase and chronic phase of caffeine use, respectively) and on the 17th and 24th days (acute abstinence and chronic abstinence, respectively).

Dependent Variables

Blood pressure (BP) behavior observed with use of the handgrip pressor test (maintain 30% of maximum force for two minutes), BP measurement was taken with the auscultatory method with a mercury column sphygmomanometer, before the test (basal measure), immediately after it and every two minutes until the eighth minute after the stimulus on the non-dominant arm and with the participant in supine position
Platelet aggregation using adenosine diphosphate, adrenalin and native collagen from equine tendon as aggregating agents and a Chromo-log aggregometer, model 520 and on the model 750 register of the same brand.

Independent Variables

750mg of caffeine daily for seven days.

Description of Actual Data Sample:

Initial N: 13 men and women
Attrition (final N): 11 men and women; one dropped out due to an important side effect and one due to acute appendicitis. 15% dropped out.
Age: Mean age 24.72 years
Ethnicity: Not specified
Other relevant demographics: None
Anthropometrics: Not applicable, no comparison group
Location: Brazil.

Summary of Results:

Other Findings

Most common symptoms during caffeine intake: Insomnia (84.6%), tremors (46.1%), nausea (38.4%), polyuria (23%), diarrhea (15.4%) and polyphagia (15.4%)
Systolic blood pressure was not significantly elevated in any phase of the study
Diastolic blood pressure was significantly elevated in the acute phase (24 hours after initial caffeine intake), but not during the chronic phase or use
Diastolic blood pressure fell significantly from values before caffeine intake to values 24-hours after caffeine withdrawal
Diastolic blood pressure was significantly lower during the hand pressor test applied during the acute phase of caffeine abstinence, compared to when applied during the acute phase of caffeine intake
No significant changes in platelet aggregation.

Author Conclusion:

Caffeine increases diastolic blood pressure at the beginning of caffeine intake and the effect disappears with chronic use.

Funding Source:

Reviewer Comments:

Inclusion criteria, exclusion criteria and recruitment methods not well-defined
Most figures were unreadable
Small sample size; no power calculations done
Caffeine dose used was quite high with significant side effects and though everyone received 750mg, the actual dose varied widely, due to wide variation in weight (116 pounds to 204 pounds)
Study design seems problematic
Unclear if statistical analysis took repeated measures into consideration.

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)	N/A
	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)	No

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?	No
2.	Was the selection of study subjects/patients free from bias?		???
	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?	No
	2.2.	Were criteria applied equally to all study groups?	N/A
	2.3.	Were health, demographics, and other characteristics of subjects described?	Yes
	2.4.	Were the subjects/patients a representative sample of the relevant population?	???
3.	Were study groups comparable?		N/A
	3.1.	Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT)	N/A
	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?	N/A
	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.)	N/A
	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?		???
	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%.)	???
	4.3.	Were all enrolled subjects/patients (in the original sample) accounted for?	Yes
	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?		N/A
	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.)	N/A
	5.3.	In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded?	N/A
	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?		???
	6.1.	In RCT or other intervention trial, were protocols described for all regimens studied?	Yes
	6.2.	In observational study, were interventions, study settings, and clinicians/provider described?	N/A
	6.3.	Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect?	???
	6.4.	Was the amount of exposure and, if relevant, subject/patient compliance measured?	No
	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?	N/A
	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?	No
	7.7.	Were the measurements conducted consistently across groups?	N/A
8.	Was the statistical analysis appropriate for the study design and type of outcome indicators?		???
	8.1.	Were statistical analyses adequately described and the results reported appropriately?	No
	8.2.	Were correct statistical tests used and assumptions of test not violated?	???
	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)?	???
	8.6.	Was clinical significance as well as statistical significance reported?	No
	8.7.	If negative findings, was a power calculation reported to address type 2 error?	No
9.	Are conclusions supported by results with biases and limitations taken into consideration?		No
	9.1.	Is there a discussion of findings?	Yes
	9.2.	Are biases and study limitations identified and discussed?	No
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