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NA: Dietary Factors and Effect on Sodium and Blood Pressure (2010)

Citation:
 
Study Design:
Class:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:
To assess the blood pressure response to changes in sodium and potassium intake and examine effect modification by age, gender, blood pressure, body weight and habitual sodium and potassium intake.
Inclusion Criteria:
  • Randomized design
  • Adult study population (mean age, 18 years or above)
  • Publication date after 1966.
Exclusion Criteria:
  • Overlap with trials already selected for the study (N=16)
  • Lack of blood pressure data (N=4)
  • Cointervention from which the effect of sodium or potassium could not be separated (N=34)
  • Diseased study population (e.g., renal diabetic patients, N=8)
  • Non-placebo control group (N=5)
  • Less than two weeks of intervention (N=57)
  • Markedly outlying blood pressure reductions (N=1).
Description of Study Protocol:
  • Recruitment: Randomized trials of sodium reduction or potassium supplementation and blood pressure were identified through reference lists of meta-analysis papers, systematic reviews and an additional MEDLINE search (January 1995 to March 2001)
  • Design: Meta-analysis
  • Intervention: Randomized trials of sodium and potassium intake for at least two weeks. For trials that entered the study, data was abstracted.

Statistical Analysis

  • Blood pressure effects of changes in electrolyte intake were assessed by metaregression analysis, weighted for sample sizes
  • Adjustments were made for trial design, duration, age, proportion of males, initial blood pressure, initial urinary sodium and potassium excretion and change in urinary sodium and potassium excretion during intervention
  • Analyses were repeated with adjustment for potential confounders such as initial body weight and change in body weight during intervention.
Data Collection Summary:
  • Timing of measurements: Trials lasting at least two weeks. 
  • Dependent variables: Blood pressure
  • Independent variables: Sodium and potassium intake.

Control Variables

  • Mean age
  • Gender
  • Body weight
  • Initial electrolyte intake
  • Initial blood pressure.
Description of Actual Data Sample:
  • Initial N: 145 out of 200 sodium trials and 47 out of 58 potassium trials met inclusion criteria
  • Attrition (final N): 105 sodium trials and 19 potassium trials were excluded, based on exclusion criteria. 40 sodium trials and 27 potassium trials in adults with a minimum of two weeks duration were selected for analysis.
  • Age: Data analyzed by age; under 45 years, over 45 years
  • Ethnicity: Data analyzed by race (Asian vs. non-Asian)
  • Location: Worldwide studies.

 

Summary of Results:

Unweighted Characteristics of Trials of Sodium Reduction or Potassium Supplementation

  Sodium Potassium
Number of Trials (Number of Strata) 40 (47) 27 (30)
Duration (week) 4 (2 to 156) 6 (2 to 114)

Age (year)

48±15

45±12
Men (%) 61±23 60±35
Initial body weight (kg) 76±6 75±8
Change in body weight (kg) -0.5 (-3.0 to 4.5) -0.2 (-1.0 to 1.6)
Initial Urinary Na Excretion (mmol/d) 153±33 157±30
Initial Urinary K Excretion (mmol/d) 66±11 60±11
Change in Urinary Na Excretion (mmol/d) -91±52 3±16
Change in Urinary K Excretion (mmol/d) -0.5±5 51±26
Initial SBP (mmHg) 144±17 143±21
Initial DBP (mmHg) 88±12 89±14
Change in SBP (mm Hg) -4.1±4.1 -3.3±4.0

Change in DBP (mm Hg)

-2.5±2.9

-2.1±3.6

Other Findings

  • Sodium reduction (median, -77mmol per 24 hours) was associated with a change of -2.54mm Hg (95% CI: -3.16, -1.92) in SBP and -1.96mm Hg (95% CI: -2.41, -1.51) in DBP
  • Corresponding values for increased potassium intake (median, 44mmol per 24 hours) were -2.42mm Hg (95% CI, -3.75, -1.08) in SBP and -1.57mm Hg (95% CI, -2.65, -0.50) in DBP
  • Blood pressure response was larger in hypertensives than normotensives, both for sodium (SBP: -5.24 vs. -1.26mm Hg, P<0.001; DBP, -3.69 vs. -1.14mm Hg, P<0.001) and potassium (SBP, -3.51 vs. -0.97mm Hg, P=0.089; DBP, -2.51 vs. -0.34mm Hg, P=0.074).
Author Conclusion:
In conclusion, reduced sodium intake and increased potassium intake could make a substantial contribution to the prevention of hypertension, especially in populations where blood pressure is already elevated.
Funding Source:
Not-for-profit
0
Foundation associated with industry:
Reviewer Comments:

Data was weighted on sample size and adjusted, but did not analyze for study quality or discuss similarity of interventions.

Quality Criteria Checklist: Review Articles
Relevance Questions
  1. Will the answer if true, have a direct bearing on the health of patients? Yes
  2. Is the outcome or topic something that patients/clients/population groups would care about? Yes
  3. Is the problem addressed in the review one that is relevant to dietetics practice? Yes
  4. Will the information, if true, require a change in practice? Yes
 
Validity Questions
  1. Was the question for the review clearly focused and appropriate? Yes
  2. Was the search strategy used to locate relevant studies comprehensive? Were the databases searched and the search termsused described? ???
  3. Were explicit methods used to select studies to include in the review? Were inclusion/exclusion criteria specified andappropriate? Wereselectionmethods unbiased? Yes
  4. Was there an appraisal of the quality and validity of studies included in the review? Were appraisal methodsspecified,appropriate, andreproducible? ???
  5. Were specific treatments/interventions/exposures described? Were treatments similar enough to be combined? ???
  6. Was the outcome of interest clearly indicated? Were other potential harms and benefits considered? Yes
  7. Were processes for data abstraction, synthesis, and analysis described? Were they applied consistently acrossstudies and groups? Was thereappropriate use of qualitative and/or quantitative synthesis? Was variation in findings among studies analyzed? Were heterogeneity issued considered? If data from studies were aggregated for meta-analysis, was the procedure described? Yes
  8. Are the results clearly presented in narrative and/or quantitative terms? If summary statistics are used, are levels ofsignificance and/or confidence intervals included? Yes
  9. Are conclusions supported by results with biases and limitations taken into consideration? Are limitations ofthe review identified anddiscussed? Yes
  10. Was bias due to the review's funding or sponsorship unlikely? Yes