Have you heard of something called quercetin?  It’s another trendy substance that is beneficial for health  – but what is it and is it worth the hype? 

 

What is Quercetin? 

Quercetin is a flavonoid, a natural pigment found in plants. It is particularly beneficial due to it being antioxidant and anti-inflammatory in nature.  Antioxidants are big business and rightly so – oxidation is a natural process in our body but when there is too much oxidation then we can get chronic inflammation and damage to our tissues and cells which eventually leads to disease. 

Unresolved oxidation in the body is known to cause asthma, bronchitis, arthritis, mental conditions and brain disorders such as dementia, cardiovascular disease, eye diseases such as cataracts. diabetes and various cancers. (1) 

 

What the heck is oxidation? 

The simple definition is a chemical reaction that takes place when a substance comes into contact with oxygen or another oxidizing substance. Examples of oxidation would be the browning of an apple or rust on metal.  Adding lemon juice to the apple would stop it going brown and so the lemon juice is an antioxidant. 

Whilst our body does make its own antioxidants, we get most of our antioxidants from plants in our diet – quercetin is one of those antioxidants. (2) 

Quercetin is one the most abundant of all the flavonoids found in our food with consumption being anywhere between 10-100mg/day depending on plant consumption. (2- 3)

 

Foods rich in quercetin include (3):

• Onions
• Apples
• Grapes
• Berries
• Broccoli
• Citrus
• Cherries
• Green tea
• Coffee (yay)
• Red wine (yay again)
• Capers (not so excited)

 

It can also be taken in supplemental form (either on its own or in a formula with other nutraceuticals, vitamins and minerals) for a variety of reasons such as reducing inflammation or allergic reactions and supporting our immune system.

 

Reducing Inflammation

This is largely through its role as an antioxidant.  One study on women with rheumatoid arthritis found that 500mg/day in supplemental form over 2 months significantly reduced stiffness and pain and improved quality of life. (4)

 

Reducing Allergic Reactions

Most of the studies done on allergy have been done in labs and on animals rather than humans but so far the results have been promising showing a reduction in histamine and anaphylactic reactions. (5)

 

Reducing Brain Degeneration

Quercetin (rather than caffeine) has been shown to have brain protective effects. (6) Most studies have been on mice but a mix of studies have demonstrated that quercetin may protect the brain from degeneration as a result of disease, injury or toxic chemicals. (7) 

 

Reducing Blood Pressure

Quercetin has been found to relax blood vessels and thereby reduce pressure. Both animal and human studies have shown that quercetin reduces blood pressure significantly.  A meta-analysis in 2016 showed that >500mg/day significantly reduced both systolic and diastolic blood pressure. (8.9)

 

Gut Health as a Possible Mechanism

Quercetin has been shown to both enhance the intestinal barrier via the tight junctions and reduce inflammation thereby reducing the risk of ‘leaky gut’ and it also modulates the composition of gut microbiota all of which protects from diseases of the colon and also indirectly other diseases. (10)

Certain types of gut bacteria including Bacteroides spp., Streptococcus spp., Bifidobacterium spp., Pediococcus spp., and Lactobacillus spp.  ferment quercetin and as a result other products (metabolites) are produced such as short chain fatty acids, bacteriocins, bile acids, amino acids and vitamins ) which then travel into the bloodstream to the liver. The liver then distributes them to specific organs in the body such as the brain, the spleen, the heart or back to the gut. These metabolites modulate inflammation, hormone production, immunoregulation and fat metabolism and reduce the risk of gut diseases, obesity, cardiovascular diseases, brain diseases and cancer. (10) 

 

My Top Tips

1. Eat a wide variety of plants every day, every week.  Foods to include: 

• Onions, shallots, leeks
• Capsicums (yellow and green)
• Cherries, berries and grapes
• Apples (especially red)
• Tomatoes (organic have been found to have more quercetin in than non-organic – up to 79% more) (11). Not the case for other veggies or fruit
• Broccoli and kale
• Asparagus (cooked only)
• Lettuce (red leaves)
• Tea (green and black)
• Coffee
• Red wine

2. It appears that absorption of quercetin is improved when eating alongside fibre rich foods, fat and alcohol. Think Mediterranean diet!
3. Don’t peel veg and fruit if you can help – a lot of the quercetin is in the skin and peel! 
4. You can take it in supplemental form, Research suggests that between 500–1,000 mg per day is effective and safe (although safety of quercetin in supplemental form isn’t confirmed in pregnancy or breastfeeding) but it’s considered more beneficial when in a mix rather than on its own due to it being poorly absorbed on its own. 

 

References

1. https://pubmed.ncbi.nlm.nih.gov/23675073/
2. https://pubmed.ncbi.nlm.nih.gov/18417116/. 
3. https://pubmed.ncbi.nlm.nih.gov/18827577/
4. https://pubmed.ncbi.nlm.nih.gov/27710596/
5. https://pubmed.ncbi.nlm.nih.gov/20548131/
6. https://pubmed.ncbi.nlm.nih.gov/27479153/. 
7. https://pubmed.ncbi.nlm.nih.gov/26904161/
8. https://pubmed.ncbi.nlm.nih.gov/11325801/
9. https://pubmed.ncbi.nlm.nih.gov/27405810/
10. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8621968/#
11.  https://pubmed.ncbi.nlm.nih.gov/17590007/

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