Abstract
Phytochemicals have received a considerable attention in the present day world. Epidemiological studies have established that phytochemicals contribute more qualitatively to the total antioxidant activity of foods than nutrient antioxidants like vitamin C and vitamin E. Among polyphenols, quercetin constitutes the main flavonoid in our daily diet being particularly abundant in onions and apples. Since the realization that many folk medicines in use contain flavonoids, interest in this class of compounds has intensified. Quercetin acts as a strong reducing agent, which together with other dietary reductants such as vitamin C, vitamin E, and carotenoids protect body tissue against oxidative stress. Recent reports suggest that quercetin as antioxidant improves normal cell survival and as pro-oxidant induces apoptosis in cancerous cells whereby prevents tumor proliferation. Among other important properties like modulation of genes related to cell cycle, signal transduction, and xenobiotic metabolism, quercetin has also been attributed with antiviral, anti-inflammatory, antibacterial, and muscle-relaxing properties. In the literature, only a few in vivo studies have been carried out; therefore, before making any authentic health claim about this compound, it is essential to know its nature and its dietary origin. Furthermore, it is important to know the amount present in different diets and its bioavailability, followed by clinical trials and investigations, if researchers are to use it as an chemo-preventive and chemotherapeutic agent against various deleterious degenerative diseases.