General Overview:

Phytochemicals, compounds derived from plants, have been utilized for centuries to address a variety of conditions. Among these, quercetin, a potent antioxidant, emerges as a notable phytochemical with therapeutic attributes crucial for overall well-being.

Understanding Quercetin:

Quercetin is a naturally occurring phytochemical categorized as a flavonol, a subset of flavonoids. It usually takes the form of quercetin glycoside, which can bind with glucose, xylose, and rutinose, enhancing its water solubility in comparison to quercetin itself, which exhibits poor water solubility. Common sources of quercetin include black tea, red wine, various fruits (grapes, apples, berries, and citrus fruits), as well as certain vegetables (onions, tomatoes, and kale). Its concentration and availability vary based on the sources. In addition to imparting color to certain plant parts, quercetin offers numerous therapeutic advantages for human health. (Salehi et al., 2020)

Role of Quercetinin the Body:

The bioavailability of quercetin hinges on three crucial processes that transpire within the body post-consumption: absorption, metabolism, and elimination. Quercetin absorption fluctuates based on its bonded form with specific sugars. Quercetin glycoside (found in onions, for instance) and quercetin glucuronide exhibit superior absorption compared to pure quercetin or quercetin linked to rutinosides (found in tea). Following ingestion, quercetin withstands the stomach's acidic pH and is absorbed via sodium-dependent glucose transporters situated in the early segments of the small intestine. Under the influence of beta-glucosidases, quercetin glycosides are cleaved, facilitating their absorption. Subsequently, quercetin undergoes processes of methylation, sulfation, and glucuronidation in various organs. Quercetin metabolites are generated by bacteria and enzymes in the small intestine, including phenolic acid. Depending on quercetin intake, metabolites and excess quercetin accumulate in pertinent organs. The excretion of quercetin metabolites correlates with its intake. (Li et al., 2016)

Benefits of Quercetin for Health:

Quercetin confers a plethora of health benefits, including:

1. Anti-inflammatory Properties: Quercetin modulates inflammation, the body's protective response to aggression. It achieves this by inhibiting lipoxygenase and cyclooxygenase enzyme activity, subsequently diminishing prostaglandin production and other inflammatory mediators like C-reactive protein and nitric oxide synthase. Additionally, it plays a pivotal role in inhibiting xanthine oxidase enzyme, linked to gout. Hence, quercetin mitigates inflammatory symptoms and enhances the quality of life for individuals grappling with systemic inflammatory disorders.
2. Cardiovascular Disease Prevention: Quercetin addresses endothelial dysfunction, curtails platelet aggregation and atheroma plaque formation, thereby augmenting blood flow to the heart and safeguarding against ischemic heart ailments. It also reduces blood cholesterol levels and offers protection against hypertension. These effects minimize the risk of heart ailments in individuals struggling with excess weight by fostering adipocyte necrosis and deterring new adipose tissue formation.
3. Neurological Disorders Protection: By influencing blood flow in cerebral vessels, quercetin prevents neurotoxins from harming neurons, thus guarding against neurodegenerative conditions such as Alzheimer's disease. Its antioxidant traits shield brain tissues from oxidative stress, ultimately enhancing cognitive function in patients with this affliction.
4. Anticancer Properties: Quercetin hampers tumor growth and thwarts metastases by inducing apoptosis in cancer cells. It additionally obstructs the production and release of growth factors, thereby curtailing cancer cell proliferation. These protective characteristics extend to colon, prostate, liver, and brain cancers.
5. Antimicrobial Property: Quercetin impedes the replication of bacterial and viral entities, effectively diminishing their infectivity. It furnishes safeguarding against numerous bacterial strains and certain viruses, like adenovirus and herpes simplex virus.
6. Hypersensitivity Reaction Prevention: By averting and diminishing the severity of allergy symptoms and allergic reactions such as asthma and colds, quercetin functions as an antihistamine, hindering histamine release.
7. Diabetic Retinopathy Protection: Quercetin obstructs the formation of vascular endothelial growth factor (VEGF), thus curbing the proliferation of retinal endothelial cells in response to elevated blood glucose levels characteristic of diabetes mellitus. This action safeguards against neurodegenerative changes in the retina and deterioration of vision. (Anand David et al., 2016)

Synergy of Quercetin and Vitamin C:

Vitamin C, also known as ascorbic acid, shares antioxidant attributes with quercetin, conferring protection to the body's cells against oxidative damage and microbial infections. Moreover, vitamin C heightens quercetin's bioavailability and collaborates with it to combat viral infections. In fact, the combination of quercetin and vitamin C thwarts viruses from entering human cells, retards their replication by inhibiting the reverse transcriptase enzyme, and bolsters the immune system's ability to counteract and eradicate harmful pathogens. (Colunga Biancatelli et al., 2020)

Conclusion:

Quercetin, a flavonol belonging to the class of flavonoid compounds found in fruits and vegetables, furnishes a multitude of advantages for human health. Its antioxidant, anti-inflammatory, anticancer, antimicrobial, antiallergic, antihypertensive, antiatherosclerotic, and neuroprotective properties render it a valuable component for addressing various health concerns. The incorporation of vitamin C amplifies the positive effects of quercetin.

References:

1. Anand David, A. V., Arulmoli, R., & Parasuraman, S. (2016). Overviews of Biological Importance of Quercetin: A Bioactive Flavonoid. Pharmacogn Rev, 10(20), 84-89. https://doi.org/10.4103/0973-7847.194044
2. Colunga Biancatelli, R. M. L., Berrill, M., Catravas, J. D., & Marik, P. E. (2020). Quercetin and Vitamin C: An Experimental, Synergistic Therapy for the Prevention and Treatment of SARS-CoV-2 Related Disease (COVID-19). Front Immunol, 11, 1451. https://doi.org/10.3389/fimmu.2020.01451
3. Li, Y., Yao, J., Han, C., Yang, J., Chaudhry, M. T., Wang, S., Liu, H., & Yin, Y. (2016). Quercetin, Inflammation and Immunity. Nutrients, 8(3), 167. https://doi.org/10.3390/nu8030167
4. Salehi, B., Machin, L., Monzote, L., Sharifi-Rad, J., Ezzat, S. M.,Salem, M. A., Merghany, R. M., El Mahdy, N. M., Kılıç, C. S., Sytar, O., Sharifi-Rad, M., Sharopov, F., Martins, N., Martorell, M., & Cho, W. C. (2020). Therapeutic Potential of Quercetin: New Insights and Perspectives for Human Health. ACS Omega, 5(20), 11849-11872. https://doi.org/10.1021/acsomega.0c01818