Quercetin is a plant pigment, from the flavonoid group of polyphenols, abundantly found in many colourful fruits, vegetables, herbs, seeds, and grains.
Studies have shown that Quercetin at appropriate doses can exhibit neuroprotective, anti-allergic, anti-oxidant, anti‐inflammatory, immunomodulatory, anti-microbial, and anti-tumour effects.
What does the evidence say about Quercetin foods or supplements to prevent or treat autoimmune diseases?
Quercetin Foods
Red onion, common onion, cranberry, blueberry and fig have 39, 20, 15, 8 and 5 mg of Quercetin aglycone per 100 g of fresh weight of edible portion, respectively.
Other common Quercetin rich foods include; Capers, Red apples, Grapes, Berries, Cherries, Kale, Broccoli, Cabbage, Citrus fruits, Peppers, Buckwheat, Green & Black Tea, Asparagus, Tomatoes, Coriander.
Quercetin can also be taken as a dietary supplement with daily recommended doses of 200–1200 mg. Dietary supplementation with quercetin is highly supported by data on its safety.
Quercetin is metabolised quickly, has poor oral bioavailability and absorption, and rapid body clearance. Evidence suggests when Quercetin is introduced in its glycosylated form, such as the compound Rutin, better absorption results are observed.
What does the science say so far?
The powerful anti-oxidant activity of Quercetin is mainly exerted via the activity of glutathione, enzymes, reactive oxygen species (ROS), and cell signalling pathways such as Nrf2, MAPK, TLR4.
The well studied anti-inflammatory effects are mainly achieved through inhibition of pro-inflammatory cytokine production eg. TNF-α, IL-1β, and IL-6.
Quercetin can reduce expression of major inflammatory genes COX1, COX2, ALOX5.
Quercetin maintains the stability of mast cells, by downregulating inflammatory mediators and allergic responses.
Quercetin significantly induces the gene expression and production of Th-1 derived IFN-γ and down-regulates Th-2 derived IL-4, resulting in immune balance.
Studies on Quercetin in Autoimmune Diseases:
Rheumatoid Arthritis (RA)
In a randomised, controlled clinical study, Quercetin significantly alleviated morning stiffness and pain in RA patients. Quercetin has reduced arthritic scores and improved symptoms significantly in RA mice. In another murine arthritis model, Quercetin reduced IL-1β, TNF-α cytokines, and inhibited NF-κB and Nrf2 signalling.
Irritable Bowel Disease (IBD)
Studies support Quercetin as promising potential for IBD. Oral Rutin, releases the active biomolecule Quercetin at the site of inflammation, and may be an effective therapy for IBD.
Multiple Sclerosis (MS)
In a study conducted using peripheral blood mononuclear cells from MS patients, treatment with Quercetin reduced their proliferation, and modulated levels of inflammatory IL-1β, MMP-9, and TNF-α. Through various immune mechanisms, studies suggest Quercetin may be useful in the complementary treatment for MS.
Lupus
Quercetin reduced symptoms of lupus nephritis in a lupus mouse model, partly via inhibition of CD4+ T cell activation and inflammatory reactions by macrophages.
Graves Disease
Quercetin can reportedly inhibit DNA damage by modulating oxidative stress in lymphocytes from Graves’ disease patients.
Atopic Dermatitis
In a mouse model of atopic dermatitis, treatment with Quercetin reduced concentrations of the inflammatory cytokines; TNF-α, CCL17, IL-4, IL-6, IFN-γ in skin tissues, downregulated NF-κB inflammatory pathways and upregulated the anti-inflammatory Nrf2 pathway.
Oral Lichen Planus (OLP)
Quercetin inhibited the proliferation and migration of T lymphocytes in the OLP immune microenvironment. It also led to a considerable increase in the level of IFN-γ and decreased level of IL-6, which interfered with the Th1/Th2 balance to modulate the immune system.
What can we conclude?
Without a doubt, a diet rich in Quercetin foods and/or safe supplementation is beneficial for immune balance, antioxidant and anti-inflammatory benefits, which are all essential for Autoimmune patients.
Using Quercetin to actually treat Autoimmune diseases will require further studies and randomised clinical trials. Most of the underlying mechanisms have been reported in animal models and need to be demonstrated for their pharmacological application. It is necessary to study doses further to detect any detrimental side effects however, Quercetin's potential is an exciting prospect.
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