Sounds strange! But onion really fights heat and cold. In summer time, the Sulphur rich onion would keep your body cool and regulate the heat effectively, thus would protect you against sun-stroke. Similarly, during cold winter time, onion would protect you against cold and flu attacks. It has strong anti-viral properties that will work against flu virus.
Onion is loaded with phyto-chemical compounds Allyl disulphide and allium which gets converted into allicin because of the cutting and crushing of the leaves. Allicin has anti-mutagenic properties that fights against the cancer cells. Research has also shown that this compound controls the blood sugar levels due to its unique anti-diabetic properties.
Like all other vegetables of Allium Genus family, onion has also shown positive results for those suffering from hypertension. Allicin reduces the stiffness of blood vessels and hence regulates blood pressure levels. The platelet clot formation is checked because of onion and would act as savior for those at risk of peripheral vascular disease (PVD), coronary artery disease (CAD), and stroke.