a1 Nutrition, Food & Health Research Centre, Department of Nutrition and Dietetics, King's College London, Franklin-Wilkins Building, 150 Stamford Street, London SE1 8WA, UK
a2 Wolfson Centre for Age-Related Diseases, Guy's, King's and St Thomas' School of Medicine, Guy's Campus, London SE1 8RT, UK
a3 Department of Clinical Biochemistry, The Queen's University of Belfast, Institute of Clinical Science, Royal Victoria Hospital, Grosvenor Road, Belfast B12 6BJ, Northern Ireland, UK
a4 Department of Biochemistry, National University of Singapore, 10 Kent Ridge Crescent, Singapore 119260
The effect of dietary intake of flavonols (predominantly quercetin) on oxidative DNA damage was studied in thirty-six healthy human subjects (sixteen men, twenty women). The study was a randomised crossover study, comprising two 14 d treatments of either a low-flavonol (LF) or high-flavonol (HF) diet with a 14 d wash-out period between treatments. Subjects were asked to avoid foods containing flavonols, flavones and flavanols during the LF dietary treatment period and to consume one 150 g onion (Allium cepa) cake (containing 89·7 mg quercetin) and one 300 ml cup of black tea (containing 1·4 mg quercetin) daily during the HF dietary treatment. A 7 d food diary was kept during each dietary period and blood samples were taken after each dietary treatment. Products of oxidative damage to DNA bases were measured in DNA from leucocytes. The study had more than 95 % power to detect a change of 20 % in DNA damage products Plasma vitamin C and plasma quercetin concentrations were also measured. No significant differences in intake of macronutrients or assessed micronutrients, measured DNA base damage products, or plasma vitamin C were found between the HF and LF dietary treatments. The plasma quercetin concentration was significantly higher after the HF dietary treatment period (228·5 (SEM 34·7) nmol/l) than after the LF dietary treatment period (less than the limit of detection, i.e. <66·2 nmol/l). These findings do not support the hypothesis that dietary quercetin intake substantially affects oxidative DNA damage in leucocytes.
(Received September 08 1999)
(Revised May 24 2000)
(Accepted June 06 2000)