Chronic high intake of quercetin reduces oxidative stress and induces expression of the antioxidant enzymes in the liver and visceral adipose tissues in mice

• 0.05% and 1% diets did not significantly affect the body weight, fat accumulation, and blood components.
• 1% quercetin diet reduced the lipid peroxidation markers in the liver, epididymal adipose tissues, and small intestine.
• 1% quercetin diet induced the expression of Gpx1 and Cat in the liver and the epididymal adipose tissues.
• The transcription factor Nrf2 was induced in the nuclear fraction of the livers of mice fed the 1% quercetin diet.
• Quercetin was suggested to induce antioxidant enzymes by activating the Nrf2 pathway in the liver.

To obtain knowledge regarding the safe intake of quercetin-rich functional foods, we examined the effect of chronic and high intake of quercetin. We fed mice a standard diet containing 0.05 or 1% quercetin for 20 weeks. Both quercetin diets did not significantly affect the body weight, fat accumulation, and blood components. However, 0.05% quercetin significantly increased the glutathione/oxidized glutathione ratio in the liver. The 1% quercetin diet reduced the lipid peroxidation marker malondialdehyde in the liver, epididymal adipose tissues, and small intestine. The 1% quercetin diet significantly induced the expression of the antioxidant enzymes Gpx1, Cat, and Sod1 in the liver and Gpx1 and Cat in the epididymal adipose tissues. The transcription factor nuclear factor E2-related factor 2 (Nrf2) was slightly induced in the nuclear fraction of the livers of mice fed the 1% quercetin diet. Quercetin may induce antioxidant enzymes by activating the Nrf2 pathway in the liver.