Onions are part of the allium family of vegetables and herbs, which also includes chives, garlic, scallions and leeks.
Allium vegetables have been cultivated for centuries for not only their characteristic, pungent flavors but also for their medicinal properties. Onions can vary in size, shape, color and flavor. The most common types are red, yellow and white onion. Flavors can vary from sweet and juicy with a mild flavor to sharp, spicy, and pungent, often depending on the season in which they are grown and consumed. It is estimated that 105 billion pounds of onions are harvested each year worldwide. The possible health benefits of consuming onions include lowering the risk of several types of cancer, improving mood and maintaining the health of skin and hair.
Allium vegetables have been studied extensively in relation to cancer, especially stomach and colorectal cancers. Their beneficial and preventative effects are likely due in part to their rich organosulfur compounds. Although the exact mechanism by which these compounds inhibit cancer is unknown, possible hypothesis include the inhibition of tumor growth and mutagenesis and prevention of free radical formation. Onions are also a source of the strong antioxidant vitamin C that helps to combat the formation of free radicals known to cause cancer.
High fiber intakes from all fruits and vegetables are associated with a lowered risk of colorectal cancer.
In a study published by the Journal of the National Cancer Institute, researchers used a population-based, case-controlled study to investigate the relationship between allium vegetable intake and prostate cancer. They found that men with the highest intake of allium vegetables had the lowest risk for prostate cancer.
Esophageal and stomach cancer:
Frequent intake of allium vegetables has been inversely related with the risk of esophageal and stomach cancer. Several survey-based human studies have demonstrated the potential protective effects of consuming alliums, as well as reports of tumor inhibition following administration of allium compounds in experimental animals.
Sleep and mood:
Folate, found in onions, may help with depression by preventing an excess of homocysteine from forming in the body, which can prevent blood and other nutrients from reaching the brain. Excess homocysteine interferes with the production of the feel-good hormones serotonin, dopamine, and norepinephrine, which regulate not only mood, but also sleep and appetite as well.
Skin and hair:
Adequate intake of vitamin C is needed for the building and maintenance of collagen, which provides structure to skin and hair.