Some research suggests that eating onions may help reduce the risk of heart attack and stroke, and help control blood sugar in people with diabetes, notes WebMD. These benefits have not been conclusively proven as of 2015.
Onions contain sulfur, a chemical compound that may act as a natural blood thinner, according to Live Science. Studies done in 1992 and 2002 in the medical journal Thrombosis Research found that sulfur has anticoagulant properties and may help stop platelets from clustering in the bloodstream. An earlier study done on animals noted that sulfur intake helped to reduce and delay the onset of hypertension. More research is required to determine if the sulfurs in onions have the same effect in humans.
Chromium, a trace element found in onions, may be effective at controlling blood sugar by helping the body use insulin more efficiently. The sulfur contained in onions may also help increase insulin production in diabetics, notes Live Science. Chromium taken in a supplement form may help lower the fasting blood sugar of people with Type 2 diabetes, notes WebMD. Chromium may be more effective in higher doses.
It is unclear whether onions contain enough chromium to have a notable effect on diabetes. A 2010 study indicated that consuming red onions may temporarily lower blood sugar in patients with Type 1 and Type 2 diabetes, notes Live Science.