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Higher plasma quercetin levels following oral administration of an onion skin extract compared with pure quercetin dihydrate in humans



To investigate the plasma kinetics of quercetin derived from hard capsules filled with onion skin extract powder or quercetin dihydrate in humans.


In a randomized, single-blind, diet-controlled crossover study, 12 healthy subjects (six men and six women) aged 21–33 years were administered a single oral supra-nutritional dose of approximately 163 mg quercetin derived from onion skin extract powder (containing 95.3 % of total flavonoids as quercetin aglycone) or quercetin dihydrate (134 mg quercetin aglycone equivalent). Blood samples were collected before and during a 24-h period after quercetin administration. The concentrations of quercetin and its two monomethylated derivatives, isorhamnetin (3′-O-methyl quercetin), and tamarixetin (4′-O-methyl quercetin), were measured using HPLC with fluorescence detection after plasma enzymatic treatment.


The systemic availability, determined by comparing the plasma concentration–time curves of quercetin, was 4.8 times higher, and the maximum plasma concentration (C max) was 5.4 times higher after ingestion of the onion skin extract than after ingestion of pure quercetin dihydrate. By contrast, t max did not differ significantly between the two formulations. The C max values for isorhamnetin and tamarixetin were 3.8 and 4.4 times higher, respectively, after administration of onion skin extract than after pure quercetin dihydrate. The plasma kinetics of quercetin were not significantly different in men and women.


Quercetin aglycone derived from onion skin extract powder is significantly more bioavailable than that from quercetin dihydrate powder filled hard capsules.

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Fig. 1
Fig. 2
Fig. 3



Area under the plasma concentration–time curve

C max :

Maximum plasma concentration

k :

Elimination rate constant

t max :

Time at maximum quercetin plasma concentration C max

t 1/2 :

Elimination half-life


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We are indebted to Anke Ernst, Ute Hartung, Petra Schulz, and Martina Quambusch for excellent technical assistance, Frithjof Egert for helpful comments on data analyses, and Rudolf Wild GmbH & Company KG (Matthias Saß) for the onion skin extract. This study was supported by Grant No. EG292/3-1 of the German Research Foundation (to SE).

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Correspondence to Sarah Egert.

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The authors declare that they have no conflict of interest.

Ethical standards

The study was conducted according to the guidelines laid down in the 1964 Declaration of Helsinki, and its later amendments and all procedures involving human participants were approved by the ethical committee of the Medical Faculty of the Rheinische Friedrich-Wilhelms-Universität Bonn, Germany. Written informed consent was obtained from all participants.

Additional information

Constanze Burak and Verena Brüll contributed equally to this study.

This trial was registered at and as DRKS00004350.

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Burak, C., Brüll, V., Langguth, P. et al. Higher plasma quercetin levels following oral administration of an onion skin extract compared with pure quercetin dihydrate in humans. Eur J Nutr 56, 343–353 (2017).

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