#386 The Bland Supremacy: Salt and cardiovascular disease
CLINICAL QUESTION
Does reducing sodium intake or substituting table salt with sodium-potassium alternatives improve cardiovascular outcomes?
BOTTOM LINE
Based on one large randomized, controlled trial (RCT) in patients with hypertension/previous stroke with above average daily salt intake (example 4.8 g/day), replacing table salt with a salt substitute may decrease mortality (from ~4.5% to ~4%) and stroke (from ~3.5% to 3%) per year. Whether reducing sodium by other means reduces mortality or cardiovascular events is unknown.
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EVIDENCE
- Results statistically significant unless indicated.
- Table salt substitution (75% sodium-chloride/25% potassium-chloride), largest RCT:1
- 20,995 participants from rural China (age ~65, mean blood pressure ~154/89, 73% with stroke history, sodium intake ~4.8g at baseline),2 estimated incidence per year:
- Mortality: ~4% (salt substitution) versus ~4.5 % (usual salt), Number Needed to Treat (NNT)=200.
- Strokes: ~3% (salt substitution) versus ~3.4 % (usual salt), NNT=250.
- Systolic blood pressure: Reduced by 3.3mmHg (salt substitution) compared to continuing regular salt.
- Limitation: Likely higher than average salt intake.
- 20,995 participants from rural China (age ~65, mean blood pressure ~154/89, 73% with stroke history, sodium intake ~4.8g at baseline),2 estimated incidence per year:
- Four systematic reviews (including above trial) showed similar results for mortality.3-6
- Adverse effects:
- Serum potassium: 0.12-0.18mmol/L higher with salt substitution.3,6
- Overall, few cases severe hyperkalemia/worsening renal function. 3,6
- Limitations: Severe kidney disease excluded.1
- Sodium reduction: No RCT powered to detect change in mortality/cardiovascular events.7,8
CONTEXT
- Guidelines:
- Recommend sodium reduction (example: <2g/day) but there is no reliable way for patients to estimate sodium consumption.9
- Average sodium intake (Canadians): ~2.7-3.6g/day.10,11
- In Canada, 75% sodium-chloride/25% potassium-chloride not available. Products with different blends of salt and potassium chloride (containing 50% less sodium than regular salt) are available (example: Half-SaltTM).
- Blood pressure:
- RCT: Lowering sodium intake (~3.6 to ~2.6 grams/day) reduces BP by ~4mmHg at 2.5 years.7,8 However, this was achieved with coaching to reduce sodium; unknown if brief interventions/self-help materials helpful long-term.
- Effect of sodium substitution/reduction on blood pressure is comparable to blood-pressure medications.12
- If processed food important source of sodium intake (common in North America, but not rural China), salt substitution/reduction may have less impact.
- Focusing on healthier food choices important; the Mediterranean diet has been shown to reduce the risk of cardiovascular events.13
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