Heart/Weight/Inflammation

Quercetin

Plant flavonoid from onions and apples that may modestly support blood pressure, glucose, and inflammation markers in adults.

score

evidence

Caution

risk

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This supplement may interact with medications, medical conditions or sensitive populations. Review safety before use.

Overview

Forms

Safety

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Quick Take

Possible small cardiometabolic benefits, but don't expect big changes and choose an absorption-enhanced form.

Quercetin is a flavonoid found in onions, apples, berries, capers, kale, and tea. It appears to dampen NF-κB-driven inflammation and oxidative stress while supporting nitric-oxide signaling in blood vessels, but oral absorption varies a lot by form. Human trials suggest modest benefits for blood pressure, fasting glucose, and some inflammatory or lipid markers. It is most relevant for adults looking for small cardiometabolic support, especially when produce intake is low.

Potential benefits

Lowers systolic blood pressure

Improves fasting glucose

Lowers hs-CRP modestly

May lower LDL cholesterol

May improve endothelial function

Protocol

Amount

500-1000 mg

Frequency

Once daily or split into 2 doses

When

With meals; consistency matters more than timing, and enhanced-absorption forms may work at lower doses.

Onset Time

4-8 weeks for most biomarker changes

Who Should Consider

Adults with mildly elevated blood pressure

Adults with borderline fasting glucose

People with low flavonoid-rich produce intake

Those wanting non-stimulant cardiometabolic support

Food Sources

Capers (~15-25 mg per tbsp)
Red onions (~15-25 mg per 1/2 cup raw)
Apples with skin (~4-10 mg per medium apple)
Kale (~3-7 mg per cup cooked)
Blueberries (~3-5 mg per cup)
Black tea (~1-2 mg per cup)

How It Works

Quercetin is a polyphenol that can inhibit inflammatory signaling pathways such as NF-κB and reduce oxidative stress. In blood vessels it may improve nitric oxide availability and endothelial function, and it may also influence glucose transport and insulin signaling. Poor water solubility makes absorption a major limiter of real-world effect.

Updated 5/19/2026