Onions: a global health benefit.

Onions appear in your garden or on your grocery shelf in a variety of colors: red, yellow, white, and green. Each offers a unique flavor--from very strong to mildly sweet. In the United States, the Vidalia onion--a favorite--is known for its mild taste.

Onions can be eaten raw, cooked, fried, dried, or roasted and are commonly used to flavor dips, salads, soups, spreads, stir-fry, and other dishes. Onion oil is also used to flavor onion salt.

Onions (along with garlic, leeks, chives, scallions, and shallots) belong to the lily family. You'll find over 600 species of Allium distributed across Europe, North America, Northern Africa, and Asia. These perennial plants usually possess bulbs or thickened rhizomes and have found uses as ornamentals, vegetables, spices, or medicines. Researchers know of more than 120 different documented uses of the amazing Allium.

The Sulfur Connection

Onion and other Allium vegetables are characterized by their rich content of thiosulfinates, sulfides, sulfoxides, and other odoriferous sulfur compounds. The cysteine sulfoxides are primarily responsible for the onion flavor and produce the eye-irritating compounds that induce those pesky tears. The thiosulfinates exhibit antimicrobial properties. Onion has proven effective against Bacillus subtilis, Salmonella typhi, and E. coli. However, the onion is not as potent as garlic, since the sulfur content of onion is only about one quarter the level found in its stronger sibling.

Onions offer a variety of medicinal effects. Early American settlers used wild onions to treat colds, coughs, and asthma; and repel insects. In Chinese medicine, onions treated angina, coughs, bacterial infections, and breathing problems.

The World Health Organization (WHO) supports the use of onions for the treatment of poor appetite and to prevent atherosclerosis. In addition, extracts from this powerful herb provide relief in the fight against coughs and colds, asthma and bronchitis. An onion extract was found to decrease allergy-induced bronchial constriction in asthmatic patients.

Onions are a very rich source of fructo-oligosaccharides. These compounds stimulate the growth of healthy bifidobacteria and suppress the growth of potentially harmful bacteria and tumors in the colon. In animal studies, onions have also demonstrated some hypoglycemic activity and, in Asia, serve as a tool in traditional medicine for the treatment of diabetes.

Heart Healthy

Onions contain a number of sulfides--similar to those found in garlic--which may lower blood lipids and blood pressure. A study conducted in India found that in communities where people never consumed onions or garlic, blood cholesterol and triglyceride levels were substantially higher--and blood clotting times shorter--than in communities where people ate liberal amounts of both. Onions are a rich source of flavonoids and saponins; substances known to provide protection against cardiovascular disease.

This herb offers natural anticlotting agents, since it possesses substances with fibrinolytic activity and can suppress platelets from clumping together in the blood. This anticlotting effect closely correlates with its sulfur content. Persons taking coumarins and other anticoagulants should use onions cautiously.

Cancer Fighter

Onion extracts, rich in a variety of sulfides, provide some protection against minor growth. In central Georgia, where Vidalia onions are grown, mortality rates from stomach cancer are about half the average level for the United States. Studies in Greece have supported this statistic, showing that high consumption of onions, garlic, and other Allium herbs offers protection against stomach cancer.

Chinese with the highest intake of onions, garlic, and other Allium vegetables have a risk of stomach cancer 40 percent less than those with the lowest intake. Elderly Dutch men and women with the highest onion consumption (at least half an onion per day) boast half the level of stomach cancer compared with those consuming no onions at all.

Western Yellow, New York Bold, and Northern Red onions offer the richest concentration of flavonoids and phenolics, crowning them as the greatest antioxidant and cancer-protective varieties of the 10 onion brands tested. The milder Western White and Vidalia onions offer the lowest activity. The consumer trend to purchase the less pungent, milder onion varieties may not be the best idea wellness wise, since those with a stronger flavor and higher astringency appear to have superior health-promoting properties.

Use and Safety

Onions have a universal appeal and can be safely eaten by most people. However, consuming large quantities of onions can lead to stomach distress and gastrointestinal irritation, possibly resulting in nausea and diarrhea.

There are no known interactions with drugs except that they can hinder the action of coagulants. The average daily dose of onions for medicinal purposes is suggested to be about 50 grams (1.75 oz.).

Onions, and other Allium species, are highly valued herbs possessing culinary and medicinal value. Some of their beneficial properties may reveal themselves only after long-term use. Onions may be a useful herb for the prevention of cardiovascular disease and various cancers, as well as protection against certain infections. They're useful blood thinners and can improve lung function in asthmatics. Their chemical composition is similar to garlic, but with a reduced potency.

The more pungent varieties of onion appear to possess the greatest concentration of health-promoting phytochemicals. So let those tears flow and enjoy the health benefits of the amazing onion.

Winston F. Craig, Ph.D., R.D., is professor of nutrition at Andrews University, Berrien Springs, Michigan.