Posted on: October 7, 2025
Quercetin is an antioxidant that has many beneficial and protective effects on our health. It is present in fruits and vegetables as a flavonoid, which is a molecule that protects our cells against damage.
The numerous metabolic processes in our bodies create free radicals as a by-product, and in low levels they are not a cause of concern. However most of us are also exposed to environmental factors that increase free radicals such as radiation, pollution, heavy metals, smoking, and other toxins. With a higher amount of free radicals present, oxidative damage can result and affect the proper functioning of our cells. This is where antioxidants such as quercetin are important because they work to neutralize the free radicals.
Research has shown that quercetin is effective in the prevention and treatment of various chronic diseases including:
- Allergies & asthma – regulates inflammation and histamine release
- Arthritis – reduces pain and inflammation
- Alzheimer’s disease – protects neurons from damage
- Cancer – acts as an anti-inflammatory and anti-oxidant
- Cardiovascular disease – protects the walls of the blood vessels, helps with high blood pressure and cholesterol
- Diabetes – improves insulin sensitivity and glucose metabolism
- Viral infections – blocks viral entry into cells and can influence viral replication
Quercetin also supports healthy immune function and is helpful in reducing allergy symptoms such as eye itching, sneezing, nasal discharge, sleep disturbance and quality of life. It does this by reducing the activation of mast cells (immune cells that release the allergy-causing molecule histamine) and controlling the release of cytokines (molecules that interact with immune cells).
Certain fruits and vegetables are high in quercetin, particularly apples, onions, capers, berries, cherries, tea, asparagus, kale, cauliflower and broccoli. It is worth noting that the amount of quercetin varies based on the food and the cooking method used. Sauteed foods retain quercetin content better than boiled foods. Quercetin is also available in supplement form, and its bioavailability (the amount that you can actually absorb from the supplement) varies based on whether it is complexed with another compound or not, such as sunflower oil. In general though, quercetin is not very highly absorbed, and only about 25% is absorbed from food or supplements. Nonetheless, it has been studied to be a powerful antioxidant and an effective part of treatment for various conditions.
References:
Desai, A. S., Mohite, A. S., Pathan, D. I., Sharangdher, S. T., Koli, J. M., Brennan, C. S., … & Vishwasrao, V. V. V. Quercetin: A Versatile Flavonoid Antioxidant.
Di Petrillo, A., Orrù, G., Fais, A., & Fantini, M. C. (2022). Quercetin and its derivates as antiviral potentials: A comprehensive review. Phytotherapy Research, 36(1), 266-278.
Salehi, B., Machin, L., Monzote, L., Sharifi-Rad, J., Ezzat, S. M., Salem, M. A., … & Cho, W. C. (2020). Therapeutic potential of quercetin: New insights and perspectives for human health. Acs Omega, 5(20), 11849-11872.
Yamada, S., Shirai, M., Inaba, Y., & Takara, T. (2022). Effects of repeated oral intake of a quercetin-containing supplement on allergic reaction: a randomized, placebo-controlled, double-blind parallel-group study. Eur Rev Med Pharmacol Sci, 26(12), 4331-4345.