What Vitamins & Minerals Are in Onions?

iMichael Blann/Photodisc/Getty Images

Onions originated in Egypt, and upon their arrival in Rome became known as unio, or large pearl, translating into Middle English as unyon, explains Texas A&M University. Onions have become staples in the American diet. Laws have been made around the onion, including the one from South Carolina that forbids certain women from eating onions in public while wearing shorts. Barring that, the familiar onion is a nutritious vegetable choice.


Onions provide potassium, having about 200 mg in one medium-sized onion. Classified as an essential mineral, potassium is also a necessary electrolyte. Potassium keeps fluids from seeping out of your tissues by maintaining a positively charged ion inside the cells. A deficiency in potassium may cause hypokalemia that presents as muscle weakness, cramping, intestinal paralysis, bloating, constipation and fatigue. High dietary intake of potassium rich foods, such as onions may help prevent stroke, high blood pressure and kidney stones, according to the Linus Pauling Institute. The recommended dietary allowance for potassium is 4,700 mg per day.

Vitamin C

A medium onion may contain upwards of 20 percent of the daily recommended dietary allowance, or RDA, according to Texas A&M University. Vitamin C is an antioxidant that fights free radicals in your body. Free radicals are produced from normal metabolism or from outside toxins, such as cigarette smoke and excess sun exposure. Vitamin C, or ascorbic acid, is necessary for collagen production, a key component in the structure of blood vessels, bones, ligaments and tendons. The RDA for vitamin C is 90 mg per day.


Sodium acts as an electrolyte in your body. An average onion may contain around 10 mg of sodium, a critical element for maintaining bodily functions. Sodium is the yin to potassium's yang. While potassium maintains intracellular fluid, sodium's job is to keep extracellular fluid from entering your cells. It regulates blood pressure and plays an important role in kidney function and secretion of certain hormones. The RDA for sodium is 1.5 mg per day.