DLM: Hypertension (2010)

Citation:
 
Study Design:
Class:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:
To study the dose-response relation between salt reduction and fall in blood pressure and compare this with two well-controlled studies of three different salt intakes.
Inclusion Criteria:
  • Random allocation to either a reduced salt intake or usual salt intake (control)
  • No concomitant interventions in either group
  • Net reduction in 24-hour urinary sodium over 40mmol (2.4g of salt per day)
  • Duration of salt reduction must have been for four or more weeks
  • Study participants were not children or pregnant.
Exclusion Criteria:
None specifically mentioned.
Description of Study Protocol:
  • Recruitment: Methods not specified
  • Design: Meta-analysis
  • Intervention: Salt intake reduction for four or more weeks.

Statistical Analysis

  • Mean effect sizes were calculated by weighting each trial by the inverse of the variance
  • Weighted linear regression was used to examine the dose-response relation between the change in 24-hour urinary sodium and the change in blood pressure
  • From the regression line, the predicted falls in blood pressure with reductions in salt intake of three, six and nine grams per day were calculated.
Data Collection Summary:
  • Timing of measurements: Reduction in salt intake for four weeks or more
  • Dependent variables: Blood pressure
  • Independent variables: Reduction in salt intake.
Description of Actual Data Sample:
  • Initial N: 734 hypertensive individuals in 17 trials, 2,220 normotensive individuals in 11 trials
  • Attrition (final N): See above
  • Age: Median 50 years (range 24 to 73 years) for hypertensive; median 47 years (range 22 to 67 years) for normotensive
  • Ethnicity: Not mentioned
  • Other relevant demographics: Study duration, median six weeks (range four weeks to one year) for hypertensive, median four weeks (range four weeks to three years) for normotensive
  • Location: United Kingdom.
Summary of Results:

 

  3g/day - HTN 3g/day - Normotensive 6g/day - HTN 6g/day - Normotensive 9g/day - HTN

9g/day - Normotensive

Meta-Analysis - SBP Fall 3.6 1.8 7.1 3.6 10.7 5.4

Meta-Analysis - DBP Fall

1.9

0.8 3.9 1.7

5.8

2.5

Salt reduction Study - SBP Fall 5.6 -- 11.2 -- 16.8 --
Salt reduction Study - DBP Fall 3.2 --  6.4 -- 9.6 --
DASH - SBP Fall 5.3 3.5 10.5 7 15.8 10.5

DASH - DBP Fall

2.9

1.8 5.7 3.5

8.6

5.3

Other Findings

  • Hypertensive individuals
    • Median 24-hour urinary sodium on usual salt intake was 161mmol (9.5g salt per day, range 125 to 191mmol) and on reduced salt intake it was 87mmol (5.1g salt per day, range 57 to 117mmol)
    • Median net change in 24-hour urinary sodium was -78mmol (4.6g salt per day, range -53 to -117mmol)
    • Pooled estimates of changes in blood pressure were -5.0±0.4mm Hg (P<0.001, 95% CI: -5.8 to -4.2mm Hg) for SBP and -2.7±0.2mm Hg (P<0.001, 95% CI: -3.2 to -2.3mm Hg) for DBP
  • Normotensive individuals
    • Median 24-hour urinary sodium on usual salt intake was 154mmol (9.1g salt per day, range 128 to 200mmol) and on reduced salt intake it was 82mmol (4.8g salt per day, range 56 to 135mmol)
    • Median net change in 24-hour urinary sodium was -74mmol (4.4g salt per day, range -40 to -118mmol)
    • Pooled estimates of changes in blood pressure were -2.0±0.3mm Hg (P<0.001, 95% CI: -2.6 to -1.5mm Hg) for SBP and -1.0±0.2mm Hg (P<0.001, 95% CI: -1.4 to -0.6mm Hg) for DBP
  • All three studies demonstrated a consistent dose response to salt reduction within the range of 12 to three grams per day
  • A reduction of three grams per day predicts a fall in blood pressure of 3.6 to 5.6 in SBP, 1.9 to 3.2mm Hg in DBP in hypertensives and 1.8 to 3.5 in SBP, 0.8 to 1.8mm Hg in DBP in normotensives
  • The effect would be doubled with a six-gram-per-day reduction and tripled with a nine-gram-per-day reduction.
  • A conservative estimate indicates that a reduction of three grams per day would reduce strokes by 13% and ischemic heart disease by 10%. The effects would be almost doubled with a six-gram-per-day reduction and tripled with a 9-gram-per-day reduction
  • Reducing salt intake by nine grams per day (from 12 to three grams per day) would reduce strokes by approximately 1/3 and ischemic heart disease by 1/4 and this would prevent about 20,500 stroke deaths and approximately 31,400 ischemic heart disease deaths in the UK.
Author Conclusion:
  • In conclusion, our meta-analysis of longer-term salt reduction trials and the two well-controlled studies with three salt intakes demonstrate a consistent dose-response relation between salt intake and blood pressure within the range of 12 to three grams of salt per day
  • Importantly, the dose-response relation exists in both hypertensive and normotensive subjects
  • The current public health recommendations to reduce salt intake from nine to 12g per day to five to six grams per day will have a major effect on blood pressure and cardiovascular disease, but are not ideal
  • A reduction of three grams of salt per day will have a much greater effect and should now become the long-term target for population salt intake worldwide.
Funding Source:
University/Hospital: St. George's Medical Hospital School (UK)
Reviewer Comments:
  • Recruitment methods not specified
  • Unclear why two studies were selected for comparison
  • No analysis of study quality.
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? No
  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? No
  5. Were specific treatments/interventions/exposures described? Were treatments similar enough to be combined? Yes
  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? ???
  10. Was bias due to the review's funding or sponsorship unlikely? Yes