Hypertension

HTN: Vitamins (2007)

Citation:

Boshtam M, Morteza R, Kamran S, Sarraf-Zadegan N, Vitamin E can reduce blood pressure in mild hypertensives, Int J Vitamin Nutr Res. 2002, 72 (5): 309-314.

 
Study Design:
Randomized controlled trial (individual randomization)Triple-blind, placebo-controlled
Class:
A - Click here for explanation of classification scheme.
Quality Rating:
Neutral NEUTRAL: See Quality Criteria Checklist below.
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
Mean±SD

Placebo Group
Mean±SD

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
Mean±SD

Placebo Group
Mean±SD

Systolic BP

Initial
Final
P-Value

 

154.5±9.1
117.4±3.6
0.000

 

153.1±7.4
150.6±6.8
0.14

Diastolic BP

Initial
Final
P-Value

 

95.0±8.8
83.1±3.6
0.000

 

93.1±6.5
87.3±6.2
0.000

Heart Rate


Initial
Final
P-Value

 

78.9±9.8
75.9±5.6
0.011

 

72.9±5.6
71.8±3.5
0.33

  • 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
Mean±SD

Placebo Group
Mean±SD

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