HTN: Vitamins (2007)
Citation:
Study Design:
Class:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:
The purpose of this study was determine the effects of vitamin E on the systolic and diastolic blood pressure and heart rate in subjects with mild hypertension.
Inclusion Criteria:
Mildly hypertensive (SBP 40mm to 160mm Hg; DBP 90mm to 100mm Hg) people referred to the Hypertension Unit of Isfahan Cardiovascular Research Center, who were not aware of their hypertension.
Exclusion Criteria:
- Secondary hypertension or CVD risk factors other than mild hypertension
- Use of hypotensive drugs.
Description of Study Protocol:
- Recruitment: Random selection of individuals consulting the Isfahan Cardiovascular Research Center
- Design: Randomized triple-blind, placebo-controlled clinical trial (RCT with individual randomization)
- Blinding used: Triple-blind, subjects were unaware of their hypertensive status
- Intervention: Subjects were randomized to a drug group who received 200IU per day of vitamin E tablets or to a placebo group, who received daily placebo tablets for 27 weeks.
Statistical Analysis
- Independent T-test for intergroup comparisons
- Paired T-test for pre- and post-intervention comparisons
- Mean vales of all variables were compared using the repeated ANOVA test.
Data Collection Summary:
Timing of Measurements
- At baseline, personal characteristics and food frequency questionnaires were completed for all subjects
- Initial and final fasting blood viamin E levels were determined using fluorimetry
- SBP, DBP and heart rate were measured for all subjects
- Height and weight were measured
- Blood pressure was measured several times during the study period.
Dependent Variables
- Variable One: Systolic blood pressure (SBP)
- Variable Two: Diabstolic blood pressure (DBP)
- Variable Three: Heart rate.
Independent Variables
- Variable One: 200IU per day vitamin E intake
- Variable Two: BMI.
Control Variables
Daily placebo.Description of Actual Data Sample:
- Initial N: 70
- Attrition (final N): None described; 70
- Age
- 20 to 60 years old
- Drug group: 41.36±7.14 (mean±SD) years
- Placebo group: 41.0±12.45 years, P=0.06.
- Ethnicity: None given
- Other relevant demographics: None given
- Anthropometrics: All subjects were obese and the placebo group weighed less than the drug group however there was no significant difference in BMI between the groups.
Variable |
Drug Group |
Placebo Group |
P-Value |
Height (cm) |
171.18±10.78 |
166.27±7.91 |
0.092 |
Weight (kg) |
88.91±20.03 |
75.92±10.67 |
0.006 |
BMI |
30.47±7.14 |
41.0±12.45 |
0.06 |
Location
Isfahan, Iran.
Summary of Results:
Variable |
Drug Group |
Placebo Group |
Systolic BP Initial |
154.5±9.1 |
153.1±7.4 |
Diastolic BP InitialFinal P-Value |
95.0±8.8 |
93.1±6.5 |
Heart Rate Initial Final P-Value |
78.9±9.8 |
72.9±5.6 |
- Significant reductions in SBP, DPB, and heart rate were seen with vitamin E supplementation, whereas only DBP was reduced in the placebo group, when comparing changes from initial for each group (see table above).
- The changes (reductions) in HR during the course of the study were greater for the placebo group, compared to the drug (vitamin E) group, P=0.00
- SBP and DBP reductions during the course of the study were greater in the vitamin E group than for the placebo group, P<0.01 (actual data is difficult to estimate from figures)
- These results were similar for the mean reductions in SBP, DBP and HR, compared to the placebo group, P<0.003 (data not shown)
- Reductions in SBP, DBP and HR comparing the vitamin E and placebo groups were also expressed in terms of percentages as follows:
Variable |
Drug Group |
Placebo Group |
P-Value |
SBP |
-24% |
-1.6% |
<0.05 |
DBP |
-12.5% |
-6.2% |
<0.05 |
HR |
-4.3% |
-14.0% |
<0.05 |
- The mean initial serum vitamin E levels were 10.5±1.5 and 10.4±1.5mmol per L for the vitamin E and placebo groups, respectively
- These changed to 17.7±1.3 and 10.0±1.5mmol per L for the vitamin E and placebo groups, respectively.
Author Conclusion:
Vitamin E supplementation (200IU per day) for 27 weeks resulted in a steady reduction of systolic and diastolic blood pressure with a more pronounced effect on systolic blood pressure in subjects with mild hypertension.
Funding Source:
University/Hospital: | Isfahan Cardiovascular Research Center (Iran) |
Reviewer Comments:
- All subjects were obese and this was not an inclusion criteria
- An explanation for the greater reduction in heart rate in the placebo group is not given
- Serum vitamin E levels reflect differences in the vitamin E and placebo groups, however no data is given regarding dietary intake of vitamin E
- No data for comparison of confounding factors is given, just a general statement made that groups were the same for sex, physical activity, etc.
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? | N/A | |
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? | Yes | |
2.4. | Were the subjects/patients a representative sample of the relevant population? | ??? | |
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) | No | |
3.2. | Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? | No | |
3.3. | Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.) | Yes | |
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")? | Yes | |
4. | Was method of handling withdrawals described? | No | |
4.1. | Were follow-up methods described and the same for all groups? | ??? | |
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? | ??? | |
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? | Yes | |
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? | 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? | No | |
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? | Yes | |
6.4. | Was the amount of exposure and, if relevant, subject/patient compliance measured? | ??? | |
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? | No | |
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)? | ??? | |
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? | 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 | |