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. Well before potassium was recognized as an element, potassium carbonate was mixed with animal fat to make soap. The carbonate was made by extracting wood ash with water before concentration by boiling — hence the name "potash" for potassium salts.

Potassium was isolated in 1807 by Sir Humphry Davy, who obtained it through the electrolysis of very dry molten caustic potash (KOH, potassium hydroxide). Potassium collected at the cathode. Potassium was the first metal isolated by electrolysis. Davy isolated sodium by a similar procedure later in 1807. The origin of the name is from the English word "potash" (pot ashes) and the Arabic word "qali" meaning alkali (the origin of the symbol "K" comes from the Latin word "kalium").

Potassium is the seventh most abundant minerals and makes up about 1.5% by weight of the earth's crust. Potassium is an essential constituent for plant growth and it is found in most soils. It is also a vital element in the human diet. Potassium is never found free in nature, but is obtained by electrolysis of the chloride or hydroxide, much in the same manner as prepared by Davy. It is one of the most reactive and electropositive of metals and, apart from lithium, it is the least dense known metal. It is soft and easily cut with a knife. It is silvery in appearance immediately after a fresh surface is exposed.

Potassium is a very significant body mineral, important to both cellular and electrical function. It is one of the main blood minerals called "electrolytes" (the others are sodium and chloride), which means it carries a tiny electrical charge (potential). Potassium is the primary positive ion (cation) found within the cells, where 98 percent of the 120 grams of potassium in the body is found.

Potassium is very important in the human body. Along with sodium, it regulates the water balance and the acid-base balance in the blood and tissues. Potassium enters the cell more readily than does sodium and instigates the brief sodium-potassium exchange across the cell membranes. In the nerve cells, this sodium-potassium flux generates the electrical potential that aids the conduction of nerve impulses. When potassium leaves the cell, it changes the membrane potential and allows the nerve impulse to progress. This electrical potential gradient, created by the "sodium-potassium pump," helps generate muscle contractions and regulates the heartbeat.

Potassium is very important in cellular biochemical reactions and energy metabolism; it participates in the synthesis of protein from amino acids in the cell. Potassium also functions in carbohydrate metabolism; it is active in glycogen and glucose metabolism, converting glucose to glycogen that can be stored in the liver for future energy. Potassium is important for normal growth and for building muscles.

Potassium is needed for growth, building muscles, transmission of nerve impulses, heart activity, etc. Potassium, together with sodium - potassium inside the cell and sodium in the fluid surrounding the cell, work together for the nervous system to transmit messages as well as regulating the contraction of muscles.

The kidneys excrete any excesses, but deficiencies are seldom found in people on normal diets, although most people could look at increasing their potassium intake. A deficiency may result in fatigue, constipation, cramping legs, muscle weakness, slow reflexes, acne, dry skin, mood changes, irregular heartbeat, irregular pulse, lack of appetite. Low potassium leads to altered heart rhythm and muscle weakness, mental apathy, muscle cramps while exercising, muscle fatigue, physical and mental stress. Deficiency can occur with excessive fluid loss from sweating, diuretic medications, diarrhea.

If you are into bodybuilding, it is also a good idea to increase your potassium intake, since potassium is needed to maintain your muscles in good form, controlling your muscle actions, and since potassium is lost in excessive sweating and urine. A great way to include this in your diet is to have a banana, citrus fruit or even a dash of apple cider vinegar.

Potassium is well absorbed from the small intestine, with about 90 percent absorption, but is one of the most soluble minerals, so it is easily lost in cooking and processing foods. Potassium is easily lost in the urine, and if large amounts of salt is ingested, it may be wise to take a potassium supplement. If you are suffering from vomiting, diarrhea or extreme sweating you may require more potassium or if your diet includes mostly processed foods, large amounts of caffeine, alcohol, or if you take diuretic pills or laxatives. If you suffer from diabetes, or suffer from kidney problems do not take a potassium supplement without your doctors consent.

Potassium is found in a wide range of foods. Many fruits and vegetables are high in potassium and low in sodium and, as discussed, help prevent hypertension. Most of the potassium is lost when processing or canning foods, while less is lost from frozen fruits or vegetables. Leafy green vegetables such as spinach, parsley, and lettuce, as well as broccoli, peas, lima beans, tomatoes, and potatoes, especially the skins, all have significant levels of potassium. Fruits that contain this mineral include oranges and other citrus fruits, bananas, apples, avocados, raisins, and apricots, particularly dried. Whole grains, wheat germ, seeds, and nuts are high-potassium foods. Fish such as flounder, salmon, sardines, and cod are rich in potassium, and many meat foods contain even more potassium than sodium.