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Taking onion skin-derived food supplements lowers blood pressure for people with hypertension

23 September 2015

A recent study published in the British Journal of Nutrition has concluded that regular ingestion of the polyphenol quercetin (3,3’,4’,5,7-pentahydroxyflavone) may prevent cardiovascular disease due to its ability to reduce systolic blood pressure. This flavonoid is found in glycosidic form in onions, kale, unpeeled apples, berries and citrus fruits. 

Brull et al. conducted a double-blinded, placebo controlled cross over trial, administering 162 mg/d of a quercetin-rich extract (derived from onion skin) or placebo (mannitol) to the study subjects, (n=68) who were all overweight-to-obese with pre-hypertension and stage I hypertension, over a six week period. They found that among the hypertensive patients, quercetin significantly decreased systolic blood pressure observed during 24 hour ambulatory blood pressure testing with no documented side effects. No significant differences were observed in the pre-hypertensive patients, indicating that in order to detect the BP lowering properties of quercetin, a threshold of elevated BP in the patient may be required. 

This study also investigated potential mechanisms of this BP reducing effect including improvement in vascular endothelial function and decreasing ACE activity. However, no conclusive evidence of either mechanism was found. The researchers also remarked that other components of the extract, not quercetin, might be responsible for the observed effects.

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