Onions contain a number of sulfides similar to those found in garlic, both of which belong to the family of the lilies, compounds that can reduce blood lipids and blood pressure.

In India, according to statistics, those communities who did not eat onion or garlic, and cholesterol were significantly higher triglycerides and altered blood clotting times in relation to the communities that ate liberal amounts of garlic and onion.

Onions are a rich source of flavonoids, substances known for its protective property against cardiovascular disease and natural anticoagulants are also agents since they possess substances with fibrinolytic activity and can suppress platelet aggregation.

The anticoagulant effect of the onion is closely correlated with its sulfur content, which prevents blood clots and therefore strokes.

Extracts of onion to be very rich in sulfides, provide some protection against tumor growth, in central Georgia (USA) where Vidalia onions are grown, mortality rates from stomach cancer are about half the average level in the United States.

Studies in Greece have shown that high consumption of onions, garlic and herbs, Allium, are protective against stomach cancer.