Dietary Sodium and Hypertension

Dietary sodium, consumed mainly as sodium chloride, helps regulate extracellular fluid volume and nerve and muscle function. When intake persistently exceeds renal excretory capacity, sodium promotes water retention and can produce a sustained rise in arterial blood pressure, especially in salt-sensitive individuals.

Volume and cardiac effects

The body maintains sodium concentration by coordinating thirst, water intake and renal excretion. Excess sodium increases extracellular fluid osmolality, stimulating thirst and water retention.

• Retained sodium and water expand extracellular and plasma volume, increasing venous return to the heart.
• Greater venous return raises stroke volume and cardiac output, which initially increases arterial pressure.

Kidney and vascular mechanisms

The kidneys normally restore sodium balance through pressure natriuresis, in which higher arterial pressure increases sodium and water excretion. If renal sodium excretion is impaired, a higher blood pressure becomes necessary to achieve sodium balance.

• Persistent volume expansion can trigger tissue autoregulation, increasing peripheral vascular resistance and converting an initial volume-driven rise into sustained hypertension.
• High sodium intake may also impair endothelial relaxation and increase arterial stiffness, further raising vascular resistance and systolic pressure.

Why the response differs among people

The blood-pressure response to sodium varies, a phenomenon called salt sensitivity. It is greater when renal sodium handling or vascular adaptation is impaired.

• Salt sensitivity is more common with older age, chronic kidney disease, diabetes, obesity and certain genetic backgrounds.
• Low dietary potassium can weaken sodium excretion and vascular relaxation, magnifying sodium's blood-pressure effect.
• Because much sodium comes from processed foods, total intake may remain high even without adding salt during meals.