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HTN: Potassium (2015)

Citation:
 
Study Design:
Class:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:
To characterize relationships between sodium and potassium intakes and blood pressure control.
Inclusion Criteria:
  • Aged 60 to 79 years
  • Baseline blood pressure under 145/85 while on a single antihypertensive medication.
Exclusion Criteria:
Not mentioned in this follow-up article.
Description of Study Protocol:
  • Recruitment: All participants of the Trial of Nonpharmacologic Interventions in the Elderly (TONE)
  • Design: Reanalysis of study data from a randomized controlled trial
  • Intervention: Subjects randomized to usual care, weight loss only, sodium reduction only or combined weight loss-sodium reduction.

Statistical Analysis

  • Pooled estimates of electrolyte intakes were developed using hierarchical measurement error models and related to non-pharmacologic blood pressure control
  • Logistic regression was used to relate the pooled estimates of long-term changes in electrolyte intakes with blood pressure control
  • Relationship in participant subgroups were examined and the consistency of the relationships was assessed using interaction terms.
Data Collection Summary:

Timing of Measurements

  • 24-hour recalls administered twice before randomization, at nine, 12, 18, 24, 30 months post-randomization and at close-out visit
  • Urinalysis collected twice at baseline, at nine, 18 and 30 months post-randomization and at close-out visit.

Dependent Variables

Blood pressure control.

Independent Variables

  • Dietary group assignment measured through 24-hour diet recalls and 24-hour urine assays
  • Data obtained by trained, certified technicians, who conducted standardized interviews using computer guided software.

Control Variables

 Average weight change.
Description of Actual Data Sample:
  • Initial N: 873 participants, 415 female, 458 male
  • Attrition (final N): 873 included in analysis
  • Age: 684 were aged 60 to 69 years, 189 were aged 70 to 79 years 
  • Ethnicity: 207 were African-American, 666 were "Other"
  • Anthropometrics: Comparability of groups not mentioned in this article
  • Location: Multi-center.
Summary of Results:

 Odds Ratio (and 95% CIs) of Blood Pressure Control

  100mmol per 24-hour Decrease in Sodium Intake P-Value 50mmol per 24-hour Increase in Potassium Intake P-Value
All Subjects 2.93 (1.84, 4.64) <0.0001 2.00 (1.13, 3.55) 0.02

<5 years HTN

1.99 (1.21, 2.65)

 <0.001

1.65 (0.55, 4.93)

0.69

5+ years HTN

11.26 (4.81, 26.40)

 <0.001

2.13 (1.12, 4.06)

0.69
SBP <125 7.56 (3.84, 14.89) <0.001 1.64 (0.66, 4.03) 0.55
SBP 125-134 2.30 (1.11, 4.80) <0.001 1.59 (0.58, 4.37) 0.55
SBP 135-144 1.32 (0.68, 2.59) <0.001 3.00 (1.14, 2.62) 0.55
DBP <75 3.36 (1.99, 4.66) 0.37 1.21 (0.59, 2.48) 0.04
DBP 75-79 2.76 (1.23, 4.99) 0.37 2.97 (1.04, 8.51) 0.04
DBP 80-84 1.57 (0.56, 3.34) 0.37  9.41 (1.90, 46.69) 0.04

Other Findings

  • Relative decreases in sodium and increases in potassium intakes each had graded relationships with better blood pressure control
  • After adjustment for measurement error, a 100-mmol 24-hour decrease in sodium intake was associated with an odds ratio of 2.93 (95% CI: 1.83, 4.64) for maintaining non-pharmacologic blood pressure control throughout follow-up
  • A 50mmol 24-hour increase in potassium intake was associated with an odds ratio of 2.00 (95% CI: 1.12, 3.55)
  • These relationships were independent of each other and of baseline levels of intakes
  • Blood pressure control was most strongly associated with sodium intake for participants with lower SBP and longer duration of hypertension and with potassium for those with elevated DBP.
Author Conclusion:
  • Sodium and potassium intakes exert independent graded influences on non-pharmacological blood pressure control
  • Correlated measurement error may spuriously introduce a dependency among these relationships
  • TONE data support the existence of a potassium-independent benefit of sodium reduction on blood pressure control in older adults
  • The control rates achieved with the greatest decreases in sodium intake have tremendous public health and medical care cost implications for both the treatment of hypertension and preventing or mitigating its complications.
Funding Source:
Reviewer Comments:
Follow-up article of TONE with more sophisticated statistical analysis, confirming previous findings about sodium and relaying observations about potassium intake although the TONE interventions were not designed directly to influence potassium intake.
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? 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? Yes
  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? 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