Sodium

What Is Sodium?

Sodium is a major mineral and electrolyte that is essential for life. It is the principal positively charged ion (cation) in the fluid surrounding cells (extracellular fluid). The body of an average adult contains approximately 100 grams of sodium, of which about 40 percent is found in bone and the remainder in body fluids and soft tissues.

Key Functions

• Fluid balance: Sodium is the primary determinant of extracellular fluid volume. It draws water by osmosis, regulating blood volume and blood pressure.
• Nerve impulse transmission: The sodium-potassium pump (Na+/K+-ATPase) creates the electrochemical gradient required for nerve and muscle action potentials.
• Nutrient absorption: Sodium-coupled transporters in the intestine co-transport glucose and amino acids across the gut wall.
• Acid-base balance: Sodium bicarbonate and sodium phosphate buffer systems help maintain blood pH near 7.4.

Dietary Reference Values and Food Sources

The Adequate Intake (AI) for sodium for adults is 1,500 mg per day. The Chronic Disease Risk Reduction (CDRR) intake — the level above which reducing intake is expected to reduce cardiovascular risk — is 2,300 mg per day, equivalent to about one teaspoon of table salt. Most Americans consume 3,400 mg/day or more.

Processed and restaurant foods account for roughly 70 percent of dietary sodium intake. High-sodium foods include:

• Table salt and soy sauce
• Canned soups and vegetables
• Cured meats (bacon, ham, salami)
• Bread and baked goods
• Cheese and condiments

Health Implications

Chronically high sodium intake is associated with elevated blood pressure (hypertension), a major risk factor for heart disease and stroke. The kidneys are responsible for excreting excess sodium; when intake consistently exceeds excretory capacity, blood volume expands and blood pressure rises. Individuals who are "salt-sensitive" — including older adults, people with hypertension, diabetes, or chronic kidney disease, and Black individuals — experience greater blood-pressure responses to sodium. Hyponatremia (low blood sodium) can occur with excessive water intake, severe vomiting, or certain medications and is a medical emergency.