Meta-analysis or Systematic Review

M - Click here for explanation of classification scheme.

POSITIVE: See Quality Criteria Checklist below.

To estimate the effects of low-sodium vs. high-sodium intake on blood pressure (BP) renin, aldosterone, catecholamines and lipids.

Studies randomizing persons to low-sodium and high-sodium diets evaluating at least one of the parameters such as:

• Blood pressure
• Renin
• Aldosterone
• Catecholamines
• Lipids.

Studies systematically investigating unhealthy patients with diseases other than elevated BP.

Recruitment

Randomized controlled trials allocating persons with normal or elevated BP irrespective of race and age to either a low-or a high-sodium diet and in which the sodium intake was estimated by the 24-hour urinary sodium excretion (either measured on the basis of a 24-hour urine collection or estimated from a sample of at least eight hours).

Design

Systematic literature review.

Statistical Analysis

• Two authors independently recorded the following data from each trial such as the sample size, the mean age of participants, the fraction of females, males, Caucasians, blacks and Asians
• The duration of interventions, the sodium reduction measured as the difference between 24-hour urinary sodium excretion during low-sodium and high-sodium diets and SD
• SBP (SD) and DBP (SD) before and after intervention
• Difference between changes in SBP and DBP obtained during low-sodium and high-sodium diets and the SD of these differences
• For crossover studies, when possible, the overall effect estimate and SE
• Levels of hormones and lipids in the blood and their SD during low-sodium and high-sodium diets
• Concerning lipids, cholesterol units of mmol per L were transformed to mg per dL by means of the factor 38.6; triglyceride units of mmol per L were transformed to mg per dL by means of the factor 88.4
• If there were discrepancies between reviewers, they looked at the data together and came to an agreement.

Timing of Measurements

An electronic literature search in PUBMED, EMBASE and Cochrane Central was performed using the following combinations of search terms:

• Salt or sodium
• Restriction or dietary
• Terms of outcome measures
• Randomized or random.

 Dependent Variables

Outcome measures were effects on:

• Systolic blood pressure (SBP)
• Diastolic blood pressure (DBP)
• Renin
• Aldosterone
• Adrenaline
• Noradrenaline
• Triglyceride
• Cholesterol
• LDL and HDL.  

• Initial N: 167 studies
• Attrition (final N): 167 studies
• Location: Denmark.

 

Key Findings

• A total of 167 studies were included
• The effect of sodium reduction in Normotensives:
  • Caucasians: SBP -1.27mm Hg (95% CI: -1.88, -0.66; P=0.0001); DBP -0.05mm Hg (95% CI: -0.51, 0.42, P=0.85)
  • Blacks: SPS -4.02mm Hg (95% CI: -7.37, -0.68; P=0.002); DBP -2.01mm Hg (95% CI: -4.37, 0.35; P=0.09)
  • Asians: SBP -1.27mm Hg (95% CI: -3.07, 0.54; P=0.17); DBP -1.68mm Hg (95%CI: -3.29, -0.06; P=0.04).
• Hypertensives:
  • Caucasians: SBP -5.48mm Hg (95% CI: -6.53, -4.43; P<0.00001); DBP -2.75mm Hg (95% CI: -3.34, -2.17; P<0.00001)
  • Blacks: SBP -6.44mm Hg (95% CI: -8.85, -4.03; P=0.00001); DBP -2.40mm Hg (95% CI: -4.68, -0.12;P=0.04)
  • Asians: SBP -10.21mm Hg (95% CI: -16.98, -3.44; P=0.003); DBP -2.60mm Hg (95% CI: -4.03, -1.16; P=0.0004)
• Sodium reduction resulted in significant increases in:
  • Renin (P<0.00001)
  • Aldosterone (P<0.000001)
  • Noradrenaline (P<0.00001)
  • Adrenaline (P<0.0002)
  • Cholesterol (P<0.001)
  • Triglycerides (P<0.0008).

Sodium reduction resulted in a significantly decrease in BP of 1% (normotensives), 3.5% (hypertensives); and a significant increase in plasma renin, plasma aldosterone, plasma adrenaline and plasma noradrenaline; a 2.5% increase in cholesterol; and a 7% increase in triglyceride.

Not-for-profit

AP Moller Foundation