Supplement
Flavonols are plant compounds found in onions, kale, tea and berries that act as antioxidants in the body. People mostly look at them for brain health, and the evidence is limited: in one large study of older adults, those eating the most flavonols had roughly half the risk of Alzheimer's dementia. That study only observed diets, and most other findings come from lab work.
Sources: PMID 31996451
- Updated
- How we grade
- 7 studies cited
- Best evidence
- Grade C
- Conditions studied
- 2
- Outcomes
- 5
- Graded outcomes
- 0014
Evidence by condition
- Strong
- Moderate
- Limited
- Very limited
| Grade | Outcome | Effect | Size | Studies | People | Studies list |
|---|---|---|---|---|---|---|
| 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. | Improves (the measure goes down) | Moderate effect | 1 study | 921 people | ||
Studies that measured alzheimer's disease risk | ||||||
| Grade | Outcome | Effect | Size | Studies | People | Studies list |
|---|---|---|---|---|---|---|
| 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. | Improves (the measure goes up) | Small effect | 2 studies | |||
General
| Grade | Outcome | Effect | Size | Studies | People | Studies list |
|---|---|---|---|---|---|---|
| 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). | Changes; see studies | Small effect | 2 studies | |||
Studies that measured anticancer activity | ||||||
| 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. | Changes; see studies | Small effect | 1 study | |||
Studies that measured xanthine oxidase inhibition | ||||||
| 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. | Improves (the measure goes up) | Small effect | 1 study | |||
Key findings
- Alzheimer's Disease RiskImproves (the measure goes down)
- Antioxidant StatusImproves (the measure goes up)
- Anticancer ActivityChanges; see studies
Safety notes in the studies
- lowest quintile of dietary flavonol intake was associated with reduced Alzheimer's dementia risk (HR 0.52, 95% CI 0.33-0.84).
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- Grade C
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Studies cited
7 studies from PubMed
- Tentatively Identified (UPLC/T-TOF-MS/MS) Compounds in the Extract of Saussurea costus Roots Exhibit In Vivo Hepatoprotection via Modulation of HNF-1α, Sirtuin-1, C/ebpα, miRNA-34a and miRNA-223.
- Dietary flavonols and risk of Alzheimer dementia.
- Flavonoid Composition and Antitumor Activity of Bee Bread Collected in Northeast Portugal.
- 3-Hydroxyflavone and structural analogues differentially activate pregnane X receptor: Implication for inflammatory bowel disease.
- Small molecule inhibitors of the HPV16-E6 interaction with caspase 8.
- Dietary flavonoids as intracellular substrates for an erythrocyte trans-plasma membrane oxidoreductase activity.
- Inhibition of xanthine oxidase by flavonoids.