Potassium is a metallic element with atomic number 19 and an average atomic weight of 39.09 daltons. Its symbol is K. It is an alkali metal and belongs to the same group as lithium, sodium, rubidium, cesium and francium. The only non-alkali element that it shares some similarities with is thallium. The thallous cation is similar in size to the potassium cation, which is the basis of the use of thallium for myocardial perfusion imaging. The thallous cation is considered a potassium cation analogue. Potassium exists physiologically in its univalent cationic state. It is the principal intracellular cation with an intracellular concentration of about 145 milliequivalents or millimoles per liter. This is 30 to 40 times greater than its extracellular concentration, which is normally 3.5 to 5.0 milliequivalents or millimoles per liter. About 98% of the body's potassium is in intracellular fluid.
The intake of potassium in a Canadian diet ranges from about 1,560 to 4,680 milligrams (40 to 120 milliequivalents or millimoles) daily. The potassium intake of vegetarians is at the high end. Foods that are rich in potassium are fresh vegetables and fruits. A medium-size banana supplies 630 milligrams of potassium or about 75 milligrams per inch; a medium orange, 365 milligrams; half a cantaloupe, 885 milligrams; half an avocado, 385 milligrams; raw spinach, 780 milligrams per three to four ounces; raw cabbage, 230 milligrams a cup; raw celery, 300 milligrams a cup. Some vegetable juices supply up to 800 milligrams per serving. A dietary intake of about 3.5 grams of potassium is considered to be a desirable intake of potassium for adults.
