Quercetin supplementation does not alter antioxidant status in humans

Abstract

This study measured the influence of ingesting quercetin on plasma measures for oxidative stress and antioxidant capacity. Male and female subjects (n = 1002) varying in age (18–85 years) and body mass index (BMI) (16.7–52.7 kg/m²) were studied. Subjects were randomized to one of three groups using double-blinded methods: placebo, 500 mg or 1000 mg quercetin/day with 125 mg or 250 mg vitamin C/day, respectively. Pre- and post-study fasting blood samples show that plasma quercetin increased in a dose-responsive manner. The pattern of change in plasma F₂-isoprostanes, oxidized low density lipoprotein, reduced glutathione, ferric reducing ability of plasma (FRAP) and oxygen radical absorbance capacity (ORAC) did not differ between supplementation groups or after adjustment for gender, age, BMI and disease status. In summary, quercetin supplementation over 12 weeks in doses of 500 mg or 1000 mg/day significantly increased plasma quercetin levels, but had no influence on several measures of oxidative stress and antioxidant capacity.

Keywords::

• Quercetin
• ferric reducing ability of plasma (FRAP)
• oxygen radical absorbance capacity (ORAC)
• F2-isoprostanes
• oxidized low density lipoprotein (LDL)
• glutathione
• antioxidant
• oxidative stress

Acknowledgements

Supported by grants from Coca-Cola and Quercegen Pharma.

Declaration of interest: D. C. Nieman is a board member of Quercegen Pharma, the remaining authors have no conflict of interest.

This paper was first published online on Early Online on 30 November 2009