Onions contain antioxidants and compounds that may reduce your risk of heart disease by fighting inflammation and lowering triglyceride and cholesterol levels.
They contain a large amount of quercetin, a flavonoid antioxidant and anti-inflammatory that may help lower high blood pressure.
A small 2015 study in 70 people with overweight and hypertension suggests that a daily dose of 162 mg of quercetin-rich onion extract may significantly reduce systolic blood pressure by 3.6 millime of mercury.