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Flavonols

Flavonols are a subclass of flavonoids found in colorful fruits, vegetables, tea, and wine. Includes quercetin (most studied), kaempferol, myricetin, and isorhamnetin. NOT to be confused with flavanols (catechins, cocoa compounds) - different spelling, different compounds. NO GRADED OUTCOMES in this category entry - see quercetin for specific evidence. Flavonols have antioxidant, anti-inflammatory, and potential cardiovascular benefits. Quercetin has the most research, showing effects on blood pressure, allergies, and exercise performance. Bioavailability is generally low but enhanced by fat and certain formulations.

Quick Answer

What it is

Flavonols are a subclass of flavonoids found in colorful fruits, vegetables, tea, and wine. Includes quercetin (most studied), kaempferol, myricetin, and isorhamnetin.

Key findings

  • Grade C: Alzheimer's Disease Risk
  • Grade D: Antioxidant Status
  • Grade D: Anticancer Activity

Safety

  • lowest quintile of dietary flavonol intake was associated with reduced Alzheimer's dementia risk (HR 0.52, 95% CI 0.33-0.84).
ℹ️ Quick Facts: Flavonols

Quick Facts: Flavonols

  • Best Evidence:Grade C
  • Conditions Studied:2
  • Research Outcomes:5
  • Key Effect:Alzheimer’s Disease
Outcomes by grade:
A0
B0
C1
D4
2 conditions · 5 outcomes

Detailed Outcomes

|
C
Alzheimer's Disease Risk
A large prospective cohort study (Rush Memory and Aging Project, n=921, mean age 81) found that highest vs. lowest quintile of dietary flavonol intake was associated with reduced Alzheimer's dementia risk (HR 0.52, 95% CI 0.33-0.84). Kaempferol showed the strongest association (HR 0.49), followed by myricetin and isorhamnetin (both HR 0.62). Interestingly, quercetin alone did not reach significance.
moderate↓Improves
D
Antioxidant Status
In vitro studies demonstrated that quercetin, myricetin, and fisetin serve as intracellular electron donors for erythrocyte trans-plasma membrane oxidoreductase, representing an additional antioxidant mechanism beyond direct radical scavenging. Quercetin metabolites isorhamnetin and tamarixetin showed comparable electron-donating activity to the parent compound.
small↑Improves
D
Anticancer Activity
In vitro screening found flavonols inhibit HPV16-E6 oncoprotein binding to caspase 8 with potency ranking myricetin > morin > quercetin > kaempferol, suggesting a novel anti-cancer mechanism. Separately, bee bread extracts rich in flavonol glycosides (quercetin, kaempferol, myricetin derivatives) showed low-to-moderate cytotoxicity against HeLa and NCI-H460 cancer cell lines (IC50 68-400 µg/mL).
small↓Worsens
D
Xanthine Oxidase Inhibition
An in vitro study found that planar flavonols with a 7-hydroxyl group (quercetin, kaempferol, myricetin, isorhamnetin) potently inhibited xanthine oxidase in a mixed-type mode with IC50 values of 0.40-5.02 µM. Authors suggested flavonols might suppress urate and reactive oxygen species formation in vivo, with potential relevance to ischemia-reperfusion injury.
small↓Worsens
D
Hepatoprotection
In a rat model, a Saussurea costus extract rich in flavonol aglycones (quercetin, kaempferol, isorhamnetin, myricetin) at 200 mg/kg significantly reduced paracetamol-induced liver damage by decreasing caspase 2, cytokeratin 18, TNF-α, and IL-6, while increasing liver catalase activity.
small↑Improves

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