What is quercetin?
Quercetin is a widely distributed flavonol compound in the plant kingdom with a variety of biological activities.
In medical research, quercetin has been found to have a variety of biological properties, including tumor inhibition, anti-free radical, antioxidant, antibacterial, anti-inflammatory, anti-allergic, hypotensive, hypolipidemic, prevent diabetes complications and immunomodulatory functions. These properties are of great significance for the treatment and prevention of cancer, aging, and cardiovascular diseases.
Food source of quercetin
Quercetin is found in a wide variety of foods, vegetables include broccoli, asparagus, shallots, green peppers, tomatoes and red lettuce, fruits such as apples, strawberries, grapes, blueberries, cranberries and blackcurrants, and even green tea contains some quercetin.
What are the empirical effects (benefits) of quercetin?
1. Quercetin assists in COVID-19 disease treatment
A 30-day randomized, controlled and open-label study of 152 COVID-19 outpatients noted:
Quercetin (daily dose of 1000 mg) is used in conjunction with standard care in the early stages of viral infection to help improve clinical outcomes, including: reduced need and duration of hospitalization, need for non-invasive oxygen therapy, intensive care unit progression, and death.
Conclusion: For COVID-19 infection, quercetin combined with standard therapy may help improve early symptoms and help reduce the severity of COVID-19 disease, but it is limited by small sample sizes and needs more large studies to further validate.
2. Quercetin regulates blood pressure
A systematic meta-analysis (7 studies with 587 participants) noted:
Quercetin supplementation has a hypotensive effect and is most effective in doses greater than 500 mg per day and more than 8 weeks of use.
Conclusion: Quercetin supplementation has the effect of regulating blood pressure, but due to insufficient sample size, heterogeneity, and short period, large studies are still needed to confirm the possibility of additional therapy for hypertension.
3. Quercetin is beneficial for blood sugar control
A systematic meta-analysis (including 9 randomized controlled trials with 781 people with metabolic syndrome and related disorders) noted:
The effect of quercetin supplementation in reducing fasting blood glucose was most significant in studies ≥ 8 weeks with a daily dose of ≥ 500 mg. In addition, the effect of quercetin in lowering insulin concentration was most significant in subjects aged < 45 years and at a daily dose of ≥ 500 mg/day.
Conclusion: For patients with metabolic syndrome and related diseases, quercetin supplementation may have a positive effect on glycemic control.
4. Quercetin is beneficial for systemic inflammation
A meta-analysis (7 randomized, double-blind controlled studies with 549 participants) noted:
Quercetin/onionin supplementation had a significant C-reactive protein reduction effect, especially in subjects with daily doses greater than 500 mg and CRP less than 3 mg/l.
Another meta-analysis (including 15 randomized controlled trials) noted:
For participants with the disease, quercetin supplementation had anti-inflammatory effects (reduced C-reactive protein and interleukin-6). The underlying mechanism may be related to inhibition of the nuclear transcription factor kB pathway, inhibition of leukotrienin formation, interference with the AMPK/SIRT1 pathway, and promotion of nitric oxide production.
Conclusion: Quercetin supplementation has a positive effect on improving systemic inflammation, but due to the heterogeneity between studies, more studies are needed to confirm it.
5. Quercetin regulates blood lipids
A systematic review and meta-analysis (16 randomized, placebo-controlled trials with 1575 participants with metabolic syndrome and related disorders) noted:
Quercetin supplementation significantly reduced total cholesterol, LDL cholesterol, and C-reactive protein levels.
Conclusion: Quercetin may have a positive effect on lipid regulation, but due to the high heterogeneity of the included studies, more large trials are needed to support it.
6. Quercetin prevents upper respiratory tract infections
A randomized, double-blind, placebo-controlled trial (12 weeks, 1002 participants of all ages) stated:
Analysis of healthy subjects over 40 years of age showed lower upper respiratory tract infection severity and total number of days in the 1000 mg daily group compared with placebo.
Conclusion: For middle-aged and middle-aged people with good health, quercetin supplementation may be helpful in preventing upper respiratory tract infections, but limited by the small sample size, more studies are still needed to support it.
7. Quercetin has good anti-cancer properties when used in synergy with curcumin.
A study of lung cancer showed:
Morphological and histological analysis of lung tumor nodules confirmed that preventive treatment with curcumin and quercetin induced apoptosis of lung tumor cells by modulating p53.
Conclusion: Curcumin and quercetin have a synergistic effect, which can inhibit the development of tumor cells through the effects of promoting apoptosis and antiproliferation.
Does quercetin have side effects?
For most adults in good health, quercetin is safe to use in moderation (less than 1000 mg daily for 12 weeks).
