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HTN: Fiber (2007)

Citation:
 
Study Design:
Class:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:
To analyze the blood pressure response to dietary therapy in the participants with stage I isolated systolic hypertension to see if the DASH diet might be a suitable treatment.
Inclusion Criteria:
  • stage I isolated systolic hypertension (SBP 140 - 159 mm Hg, DBP < 90 mm Hg)
  • participants in DASH trial
  • Aged 47 +/- 22 years
Exclusion Criteria:
Previously reported.
Description of Study Protocol:

Recruitment

DASH participants with stage I isolated systolic hypertension.

Design

Randomized Controlled Trial. 

Blinding used (if applicable)

Not possible - lab tests. 

Intervention (if applicable)

After 3-week run-in period on typical American (control) diet, participants were randomly assigned for 8 weeks to 1 of 3 diets, sodium content was same in all 3 diets and caloric intake was adjusted during the trial to prevent weight change.

  • Continuation of control diet
  • Diet rich in fruits and vegetables
  • DASH diet

Statistical Analysis

All analyses made on an intent-to-treat basis.  Between-diet differences in the change in blood pressure were tested with 1-way ANOVA with Bonferroni's adjustment for multiple comparisons.  Significance of within-diet change in blood pressure was tested with paired t tests if normally distributed, signed rank test if not.  2-way ANOVA performed for diet/gender interactions.  Abilities of diets to lower SBP to < 140 mm Hg were compared with chi-square test.

Data Collection Summary:

Timing of Measurements

Blood pressure was measured at baseline and at the end of the 8-week intervention period.  Urine samples taken at the end of the run-in and intervention periods.

Dependent Variables

  • Blood pressure measured with standard sphygmomanometry 

Independent Variables

  • Continuation of control diet, diet rich in fruits and vegetables or DASH diet
  • Participants agreed only to eat foods that were provided
  • Alcohol consumption limited to only 2 drinks per day
  • 24-hour urinary excretion of sodium, potassium and creatinine to determine compliance

Control Variables

 

Description of Actual Data Sample:

Initial N:  Among 459 participants in DASH trial, 72 had stage I isolated systolic hypertension.  Ccontrol group n=25 (60% female), fruits & vegetables n=24 (58% female); DASH n=23 (39% female).

Attrition (final N):  72 assumed, dropouts not discussed

Age:  mean age Controls:  53.6 +/- 11.8 years, Fruits & Vegetables:  52.6 +/- 8.7 years, DASH:  54.7 +/- 8.1 years

Ethnicity:  Controls:  36% nonminority, 64% minority; Fruits & Vegetables:  33% nonminority, 67% minority; DASH:  43% nonminority, 57% minority 

Other relevant demographics:

Anthropometrics: fewer women in the DASH group, but the groups were similar in age, ethnicity, BMI and baseline BP.

Location: Boston

 

Summary of Results:

Other Findings

There were no significant changes in body weight among diet groups.

Use of the DASH diet significantly lowered SBP compared with the control diet (-11.2 mm Hg, 95% CI:  -6.1 to -16.2 mm Hg, P < 0.001) and the fruits and vegetables diet (-8.0 mm Hg, 95% CI: -2.5 to -13.4 mm Hg, P < 0.01).

Overall, blood pressure in the DASH group fell from 146/85 to 134/82 mm Hg.

Similar results were observed with 24-hour ambulatory blood pressure measurements.

In the DASH diet group, 18 of 23 participants (78%) reduced their SBP to < 140 mm Hg, compared with 24% and 50% in the control and fruits & vegetables groups, respectively.

Author Conclusion:
Our results demonstrate that compared with the control diet, use of the DASH diet lowered SBP by 11.2 mm Hg in participants with stage I isolated systolic hypertension.  The DASH diet, which is rich in fruits, vegetables, and low fat dairy foods, is as effective as first-line therapy in stage I isolated systolic hypertension.
Funding Source:
Government: NHLBI, NCMHD, NCRR, NIH
Reviewer Comments:
Dropouts not discussed.  Dietary compliance checked through urinalysis.
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? Yes
  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? Yes
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) Yes
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? Yes
  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")? N/A
4. Was method of handling withdrawals described? ???
  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%.) No
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? ???
  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? Yes
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? No
  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? Yes
  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? Yes
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described? Yes
  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? Yes
  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)? Yes
  8.5. Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)? Yes
  8.6. Was clinical significance as well as statistical significance reported? Yes
  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