HTN: Potassium (2015)

Citation:
 
Study Design:
Class:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:
To investigate whether salt might be an important contributory factor for hypertension in Hong Kong Chinese patients with untreated hypertension.
Inclusion Criteria:
  • Age between 18 and 75 years
  • Essential hypertension newly diagnosed or previously diagnosed, according to WHO/International Society of Hypertension criteria, but not treated with medications.
Exclusion Criteria:
  • Significant cardiac disease, including valvular heart disease, arrhythmia, previous myocardial infarction, angina and heart failure
  • Known or suspected renal or renovascular disease
  • Liver disease
  • Edema
  • Pregnancy
  • Any serious concomitant disease
  • Patients who were on a special diet.
Description of Study Protocol:
  • Recruitment: Patients were referred to the hypertension outpatient clinic of a university teaching hospital
  • Design: Case-control study
  • Intervention: Subjects underwent several measurements, in addition to blood pressure measurements and urine collection.

Statistical Analysis

  • Spearman's rank correlation was used as normal distribution of data was not assumed
  • Stepwise multiple regression was used to investigate the relationship between DBP and independent variables
  • Logarithmic transformation of the 24-hour urinary sodium excretion resulted in slightly higher R2 values and did not affect the conclusions.
Data Collection Summary:

Timing of Measurements

  • Full medical histories, physical exams, blood tests, electrocardiogram and posteroanterior chest X-ray were completed
  • Blood pressure measurements and 24-hour urine collection performed for each patient and repeated 12 weeks later in 14 hypertensive patients who remained untreated
  • 22 hypertensive patients underwent ambulatory blood pressure monitoring.

Dependent Variables

Blood pressure measured with strict protocol under standardized conditions in a temperature-controlled environment, with the mean of three readings used for analysis. 

Independent Variables

Dietary intake of sodium measured through urine excretion.

Control Variables

  • Age
  • Gender
  • BMI
  • Ethanol intake
  • Season.
Description of Actual Data Sample:
  • Initial N: 117 subjects
    • 47 normotensive controls (21 male, 26 female)
    • 70 untreated hypertensives (43 male, 27 female).
  • Attrition (final N): See above
  • Age: Hypertensive patients mean, 46±14 years; controls mean, 41±12 years
  • Ethnicity: Not mentioned
  • Location: Hong Kong, China.
Summary of Results:

  Urinary Sodium Excretion P-Value Diastolic Blood Pressure P-Value
DBP R=0.41 <0.001    
Ambulatory DBP

R=0.47

0.026

R=0.55

0.008

Repeat DBP

R=0.60

0.02

R=0.68

0.01

SBP R=-0.01 NS R=0.28 0.02
Age R=-0.09 NS R=-0.16 NS
Gender R=-0.08 NS R=-0.21 NS
BMI R=0.16 NS R=0.33 0.007
Urinary Potassium Excretion R=0.13 NS R=-0.24 0.05

Other Findings

  • In the hypertensive patients, DBP correlated with 24-hour urinary sodium excretion (R=0.41, P<0.001), even after adjustment for age, gender, BMI, ethanol intake and season (R=0.34, P=0.02)
  • In normotensive controls, DBP did not correlate with sodium excretion (R=0.21, P=0.16)
  • A correlation between DBP and sodium excretion was also observed in the patients who underwent ambulatory blood pressure monitoring (R=0.47, P=0.026) and in repeat measurements in untreated patients (R=0.60, P=0.02)
  • SBP did not correlate with sodium excretion, although it increased with patient age (0.6±0.1mm Hg per year, P<0.001)
  • In a multiple regression analysis with DBP as the dependent variable, the regression coefficient was 0.06±0.02mm Hg per mmol sodium
  • The regression coefficients for ambulatory DBP and diastolic pressure repeated at 12 weeks were 0.07±0.03 and 0.09±0.04mm Hg per mmol sodium, respectively.
Author Conclusion:
  • In conclusion, our results show that sodium intake is strongly related to diastolic blood pressure in our hypertensive patients, accounting for 17% of the variance of diastolic blood pressure
  • Long-term reduction in salt intake may be indicated, at least in these hypertensive patients, if not the whole population.
Funding Source:
University/Hospital: Ninewells Hospital and Medical School
Reviewer Comments:
Controlled for many variables.
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) N/A
  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) N/A
 
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.) Yes
  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? N/A
  6.2. In observational study, were interventions, study settings, and clinicians/provider described? Yes
  6.3. Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect? N/A
  6.4. Was the amount of exposure and, if relevant, subject/patient compliance measured? N/A
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described? Yes
  6.6. Were extra or unplanned treatments described? Yes
  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)? 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? 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