Hypertension

HTN: Medical Nutrition Therapy (2015)

Citation:

Weinberger MH, Cohen SJ, Miller JZ, Luft FC, Grim CE, Fineberg NS. Dietary sodium restriction as adjunctive treatment of hypertension. JAMA 1988; 259 (17) : 2,561-2,565.

PubMed ID: 3357230
 
Study Design:
Non-Randomized Controlled Trial
Class:
C - Click here for explanation of classification scheme.
Quality Rating:
Positive POSITIVE: See Quality Criteria Checklist below.
Research Purpose:

To examine the effect of modest dietary sodium ion restriction in treated hypertensive individuals.

Inclusion Criteria:
  • Patients with essential hypertension in whom secondary forms of hypertension have been excluded
  • All but 18 were receiving anti-hypertensive drugs and had achieved adequate blood pressure control
  • All participants were required to enlist the co-participation of an adult household member as a partner to permit examination of various aspects of the impact of social support on compliance with dietary sodium ion restriction, and either the patient or partner was required to be the primary food preparer. 
Exclusion Criteria:

None specifically mentioned.

Description of Study Protocol:

Recruitment

Subjects were enlisted by a written or oral invitation. Patients were attending a university-based or a Veterans Administration hypertension clinic. Recruitment of patients was staggered over 18 months to avoid confounding due to seasonal variations in food choices.

Design

Non-randomized Clinical Trial 

Blinding used

Not applicable 

Intervention

  • Three visits of individualized dietary counseling with a research dietitian to achieve reduction in sodium ion intake, at weeks one, two and three
  • Dietitians used the food preference questionnaires to review and identify sources of sodium in the diet and provide alternatives.

Statistical Analysis

  • Changes over time were assessed using repeated measures ANOVA
  • When significant changes were found, multiple comparisons were made using paired T-tests and Bonferroni's correction
  • Two-by-two tables, such as those examining changes in medication, were analyzed with Fisher's exact test
  • Comparisons between patients who did and those who did not complete the study used T-tests for continuous variables and Fisher's exact test or chi-square analysis for discrete variables.
Data Collection Summary:

Timing of Measurements

Subjects were initially required to collect three 24-hour urine samples, have several blood pressure measurements made, and complete a food questionnaire designed to identify the individual's usual food preferences. Urine collections made at baseline and weeks one, two, three, four, six, 18 and 30. Blood pressure measured in the clinic on weeks one and three and in the home at weeks two, six, 18 and 30. Serum samples analyzed at baseline and weeks six, 18 and 30 weeks.

Dependent Variables

  • Blood pressure measured with sphygmomanometer 
  • Body weight measured with electronic scale
  • Serum samples analyzed for sodium, potassium and creatinine
  • Urine samples
  • Medication adjustments by physician or nurse-practitioner.

Independent Variables 

  • Three visits of individualized dietary counseling with a research dietitian to achieve reduction in sodium ion intake at weeks one, two and three
  • Dietitians used the food preference questionnaires to review and identify sources of sodium in the diet and provide alternatives.

Control Variables

 

Description of Actual Data Sample:

Initial N

114 patients

Attrition (final N)

98 completed 30 weeks (86%), 80 males and 18 females. Patients who dropped out tended to have lower diastolic blood pressures and required fewer medications for blood pressure control than completers, so they may have been less motivated to complete the study.

Age

Mean 51.9±10.7 years (range 20-72 years)

Ethnicity

97 White, 15 Black and two Oriental

Other relevant demographics

Anthropometrics

Location

Indiana

 

Summary of Results:

 

Variables

Baseline Week 1 Week 2 Week 3

Week 4

Sodium (mEq/24 h)

170±66 93±67, P< 0.001 97±64, P<0.001 95±52, P<0.001

94±52, P<0.001

Potassium (mEq/24 h)

70.5±24

76.2±29.9

72.3±30.4 69.8±27.6

74.2±28.4

Weight (kg) --- 86.4±17.3 86.4±16.8 85.5±17.3 85.5±17.7
SBP (mm Hg) --- 137±18 134±16 130±16 127±14
DBP (mm Hg) --- 87±10 84±10 83±9 81±10

Other Findings

A significant reduction in mean sodium ion intake was achieved after the first of three lessons and was maintained for 30 weeks with no change in potassium ion intake.

Significant falls in blood pressure and body weight were observed with no significant correlations noted between the two variables, implying independence of these effects.

Individuals compliant with the dietary sodium ion restriction goal (urinary excretion <80mmol/day or mEq/day) were more likely to have a reduction in the number of medications than those not reaching that goal. 

Author Conclusion:

These observations suggest that modest dietary sodium ion restriction is feasible in treated hypertensive patients and that adherence to such a regimen may permit blood pressure control with fewer medications.

Funding Source:
Government: Demonstration and Education Research in Cardiovascular Disease Grant HL 30561, US DHHS
Reviewer Comments:

Subjects were also taking blood pressure medication. Authors note that present observations suggest that a combination of dietary sodium restriction and anti-hypertensive therapy may permit blood pressure control with fewer medications and fewer side effects than would be needed without such restriction.

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? 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? Yes
  4.1. Were follow-up methods described and the same for all groups? Yes
  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%.) Yes
  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? Yes
  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.) 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? N/A
  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)? N/A
  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? 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