Until the 18th century no distinction was made between potassium and sodium. This was because early chemists did not recognise that "vegetable alkali" (K₂CO₃, potassium carbonate, coming from deposits in the earth) and "mineral alkali" (Na₂CO₃, sodium carbonate, derived from wood ashes) are distinct from each other. Eventually a distinction was made.

Sodium, from the English word "soda" (the origin of the symbol "Na" comes from the Latin word "natrium"), was first isolated in 1807 by Sir Humphry Davy, who made it by the electrolysis of very dry molten sodium hydroxide, NaOH. Sodium collected at the cathode. Davy isolated potassium by a similar procedure, also in 1807. Shortly after, Thenard and Gay-Lussac isolated sodium by reducing sodium hydroxide with iron metal at high temperatures.

Like the other alkali metals, sodium is a soft, light-weight, silvery white, reactive element that is never found unbound in nature. Sodium floats in water and decomposes it, releasing hydrogen and forming hydroxide. If ground to a fine enough power, sodium will ignite spontaneously in water. However, this metal does not normally ignite in air below 388 Kelvin.

Sodium is required by the body, but most people have a far too high intake of sodium (salt) in their diet. Sodium is an electrolyte in the body and is required in the manufacture of hydrochloric acid in the stomach, which protects the body from any infections that may be present in food.

Sodium is a vital element. The human diet must contain a sensible amount of sodium. The sodium cation is the main extracellular (outside cells) cation in animals and is important for nerve function in animals. The importance of sodium as salt in the diet was recognized well before sodium itself was understood to be an element. This recognition formed the basis of trading of salt deposits lining the Dead Sea in biblical times by the Romans. Prolonged sweating results in sodium ion loss in sweat and it is most important that the sodium ion is replaced through proper diet.

Sodium metal is a major fire risk. Sodium compounds are relatively harmless as long they are as not ingested in excess. This includes common salt, NaCl. People with heart diseases may need to ensure their diet does not contain too much sodium.

Excessive sodium may cause high blood pressure, which may lead to a host of health problems. Excessive long-term use of sodium may also cause a loss of calcium from your body.

WAYS TO DECREASE YOUR SODIUM INTAKE

• Cook from scratch. De-emphasize the use of processed foods.
• Use the salt shaker sparingly. Taste your food before adding salt. Remove the salt shaker from your table or get a shaker with smaller holes.
• Choose fresh, frozen, or canned vegetables without added salt.
• Choose fresh or frozen fish, shellfish, poultry, and meat more often than canned or processed forms.
• Snack on fresh fruits and vegetables, which are low in sodium.
• Balance a high sodium food with others of low sodium content. Limit processed, cured or pickled foods.
• Read the Nutrition Facts Label to compare the amount of sodium in processed foods - such as frozen dinners, packaged mixes, cereals, cheese, breads, soups, salad dressings, and sauces. The amount of sodium in different types and brands often varies widely.
• Ask your grocer or supermarket to offer more low-sodium foods.
• Try to keep your daily sodium intake below 2500 mg.
• Read food labels. Buy products low in sodium, MSG, baking soda and other sodium-containing compounds.
• Choose foods labeled "low-sodium, " "reduced sodium" or "sodium free."
• Take note of the sodium content of your favorite condiments, particularly meat tenderizer, steak sauce, soy sauce, salsa, and catsup.
• Use alternate spices and herbs to season your food. Fresh vegetable and citrus juices work great too.
• Some people can use salt substitutes. These are high in potassium so people with kidney or other medical problems may not be able to use them. Ask your physician first.
• Try seasoning mixes such as Mrs. Dash or Mr. Pepper.
• Choose nonprescription medications low in sodium. Ask your pharmacist about the sodium content of your prescription medication.
• When you go out to eat, choose low sodium menu items and ask that they prepare your meal without salt or MSG. Use pepper instead of salt to season your meal.