Hypertension

HTN: Medical Nutrition Therapy (2015)

Citation:

Koopman H, Spreeuwenberg C, Westerman RF, Donker AJM. Dietary treatment of patients with mild to moderate hypertension in a general practice: A pilot intervention study. (2) Beyond three months. Journal of Human Hypertension. 1990; 4: 372-374.

PubMed ID: 2258877
 
Study Design:
Randomized Controlled Trial
Class:
A - Click here for explanation of classification scheme.
Quality Rating:
Neutral NEUTRAL: See Quality Criteria Checklist below.
Research Purpose:

To study the effects of intensive dietary counseling on blood pressure and answer the questions:

  • What is the overall effect of advice based on a combination of the different recommended measures?
  • What is the best strategy for the general practitioner, dietitian and practice nurse to bring about considerable changes in nutritional habits?
Inclusion Criteria:
  • Mild to moderate hypertension: Diastolic blood pressure between 90 to 110mm Hg on three different occasions
  • No impairment in renal function
  • No use of antihypertensive drugs during at least six weeks prior to the trial
  • No use of oral contraceptives
  • BMI of not more than 27
  • No history of insulin-dependent diabetes mellitus or coronary heart disease.
Exclusion Criteria:
  • Diastolic blood pressure above 110mm Hg on three occasions
  • Increase in body weight of 5% above baseline level
  • Signs and symptoms of coronary heart disease.
Description of Study Protocol:

Recruitment

During routine consultations, patients were asked to participate in the study if they met inclusion criteria.

Design

Randomized controlled trial. 

Intervention

  • Subjects were randomized into dietary advice or control group for one year
  • Dietary advice subjects were sent to the dietitian, the control group had to wait three months before seeing the dietitian
  • Subjects visited the dietitian monthly for a dietary recall, elucidation of the principles of diet desired, weight control and individual feedback if necessary
  • Diet was of a composition considered to be appropriate and was monitored by a dietitian, with the goal intake of 85 to 100mmol sodium, 76 to 100mmol potassium, 25 to 30mmol calcium, 20mmol magnesium, 10% to 12% of energy from polyunsaturated fatty acids and 30g nutritional fibers.

Statistical Analysis

Student's T-test with 95% (90% one-tailed) confidence intervals were used for statistical analysis.

Data Collection Summary:

Timing of Measurements

Dietary counseling ended after one year. Blood pressure and urinary sodium excretion were measured monthly. Serum cholesterol, HDL cholesterol and triglycerides were measured at baseline, three months and 12 months. Patients were also asked to return six months after the end of the intervention.

Dependent Variables

  • Systolic and diastolic blood pressure using sphygmomanometer
  • Mean arterial pressure
  • Serum lipids: Total cholesterol, HDL cholesterol, triglycerides
  • Change in calculated LDL cholesterol
  • Change in sodium excretion in 24 hours, corrected for creatinine excretion.

Independent Variables

Dietary advice or control group for one year.

 

 

Description of Actual Data Sample:
  • Initial N: 35 subjects, 17 in dietary advice (eight men, nine women) and 18 in control group (eight men, 10 women)
  • Attrition (final N): 28 subjects (80%); two patients had diastolic blood pressure above 110mm Hg on three occasions, two patients because diastolic blood pressure was almost 110mm Hg and they wanted drug treatment, two patients because of suspected angina and one patient because of a stroke.
  • Age: Mean age 44±7 years in dietary advice, 46±9 years in control group
  • Anthropometrics: Differences between groups at baseline were not statistically significant
  • Location: The Netherlands.

 

Summary of Results:

 

Variables

Baseline Three months Six months Nine months 12 months 18 months

SBP (mm Hg)

144.5±11.7 -1.6 -2.7 -3.8, P<0.05  -1.6 -3.7, P<0.05

DBP (mm Hg)

95.4±6.4

-1.5, P<0.05 -4.1, P<0.01 -4.6, P<0.01

-3.6, P<0.01

-4.0, P<0.01

MAP (mm Hg) 111.8±7.3 -1.6, P<0.05 -3.7, P<0.01 -4.4, P<0.01 -2.9, P<0.01 -3.9, P<0.01
Na excretion (mmol per 24 hours) 156.3±45.0 -10.3, P<0.05 -23.7, P<0.01 -20.1, P<0.01 -29.6, P<0.01 -22.4, P<0.05

Other Findings

Significant decreases in blood pressure and sodium excretion compared to baseline occurred, while serum lipids showed transient improvement.

Pooled data of all participants showed a statistically significant decrease in diastolic blood pressure and mean arterial pressure after three and six months' dietary intervention.

After nine, 12 and 18 months, this effect leveled off, but the values remained statistically lower than at the start of the study.

Sodium excretion per 24 hours showed a similar pattern: Significant decreases after three and six months and a stabilization at nine and 12 months.  

The value at 18 months was not significantly different from that at 12 months.

The net result was that blood pressure and sodium excretion decreased significantly during the 12 months of intervention compared with baseline levels, and that this effect persisted at 18 months.

Baseline levels of serum lipids were already quite normal. 

Author Conclusion:

Our study does not permit a firm conclusion as to the cause of the effects observed because of a lack of a control group. The observed changes in blood pressure may be influenced by participation in the dietary manipulation, by exposure to the experiment itself ('placebo effect') or by the natural course of blood pressure.

Funding Source:
University/Hospital: Academic Hospital of the Free University, Amsterdam
Reviewer Comments:

Small numbers of subjects in groups. Authors note that because of a lack of control group and the small numbers involved, conclusions should be drawn with caution.

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? ???
  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) 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.) ???
  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? 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? ???
  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? 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? 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? ???
  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? Yes
  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? 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