Tier 2 — strong

Plasma concentrations and urinary excretion of the antioxidant flavonols quercetin and kaempferol as biomarkers for dietary intake

J H de Vries, P C Hollman, S Meyboom, M N Buysman, P L Zock, W A van Staveren, M B Katan
The American journal of clinical nutrition 1998 68(1):60-5

Bibliography

PubMed
PMID 9665097
DOI
10.1093/ajcn/68.1.60
Funding
Funding was not specified in the indexed record or the disclosure metadata available for this entry.
Competing interests
A competing-interest declaration was not available in the indexed record or the disclosure metadata used for this entry.

Study snapshot

DesignRandom-order crossover dietary biomarker study
ModelHuman intervention research
Sample15 adults
InterventionBlack tea or fried onions providing different quercetin amounts
Duration3-day treatments with a 4-day washout
EndpointsSource-specific outcomes described in the key findings

What the study showed, in plain terms

Published in 1998, this source examined forms, absorption and food sources. Design: Random-order crossover dietary biomarker study. Sample/model: 15 adults. The exposure or intervention was Black tea or fried onions providing different quercetin amounts. Follow-up or treatment period: 3-day treatments with a 4-day washout.

Plasma and urinary flavonols reflected short-term intake; recovery differed between tea and onions.

Dietary biomarker validation rather than clinical efficacy. Different food doses and matrices prevent a simple supplement-equivalence conclusion.

Continue with Quercetin Data Center

For topic-level interpretation, read Foods High in Quercetin: Practical Sources and Portions. This is a related guide; the citation panel separately identifies articles that directly cite this paper.

Key findings

  • Plasma and urinary flavonols reflected short-term intake; recovery differed between tea and onions.
  • The recorded outcome domains were Source-specific outcomes described in the key findings.
  • The result applies to the tested exposure: Black tea or fried onions providing different quercetin amounts; 3-day treatments with a 4-day washout.

What this study can and cannot tell us

  • Dietary biomarker validation rather than clinical efficacy. Different food doses and matrices prevent a simple supplement-equivalence conclusion.
  • An individual controlled trial must be interpreted alongside its comparator, sample size, endpoint selection and independent replication. It does not validate a different commercial formulation or a general longevity claim.
  • Source basis: Source check: PubMed abstract and indexed metadata; full methods were not independently confirmed for this entry. Missing method details, funding information or participant denominators are not inferred.

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Editorial review

Reviewed by the Biohack Blueprint research team

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Dr. Khaled Mahmoud, MBBChCritical Care Medicine, Longevity Science & Editorial Direction Dr. Amr Yasser, PhDCardiometabolic, Musculoskeletal, Gut & Bioavailability Dr. Abdulla Mostafa, PhDCellular Senescence, Neurological, Mitochondrial & Brain-Ageing Biology