Blackboard with the chemical formula of Quercetin

Quercetin & its Role in Supporting Healthy Kidney Function

Inflammation is a word we hear a lot in the world today and with good reason. It is well known to be a driver in many diseases, particularly chronic disease and if not addressed can impact healing and recovery. We know that diet, lifestyle and environmental factors are contributing factors in driving levels of inflammation and it doesn’t seem to be getting any better.

When considering kidney function and health, reducing inflammation and balancing any oxidative stress is a key component of treatment thus anti-inflammatory and anti-oxidant treatment is essential.

In this review article, I am discussing the evolving benefits of quercetin which has had extensive research over the recent years into its anti-inflammatory and anti-oxidant benefits.

Before we learn more about its benefits, what is quercetin?

What is Quercetin?

Quercetin is known as a flavonoid which is a type of polyphenol (chemicals) that are found in our foods, specifically plant-based foods, which are generally known to have many health benefits. It is one of the safest and most abundant naturally occurring compounds found in many medicinal herbs, dietary supplements and fruits and vegetables with various pharmacological actions and benefits attributed to its use.

Quercetin benefits are most commonly through its powerful anti-inflammatory activity and antioxidant properties and has a direct effect on regulating some of the body key mechanising including glutathione, enzyme activity and is involved in signalling pathways (which we will learn more about soon!).

As well as these powerful properties other actions include:

  • Anti-hypertensive
  • Anti-allergenic
  • Neuro-protective
  • Chemo-protective
  • Antibacterial effects
  • Immunoprotective

Quercetin is commonly prescribed as a supplement to assist with a diverse range of health conditions and can be found in a good health food store. As I previously mentioned it is commonly found in different plants and vegetables which emphasises the importance of a diverse plant-based diet.

Some foods that contain higher amounts of Quercetin include:

Fruits

Apples, cranberries, cherries, grapes, oranges

Vegetables

Onion, peppers, asparagus, lettuce, tomatoes, potatoes, brassica vegetables, broccoli, garlic

garlic rich in quercetin

Other foods

Black and green tea, nuts,

Herbs

Gingko Biloba, Hypericum perforated (St Johns Wort), Sambucus cana denses (Elder)

The bioavailability of quercetin (the amount that reaches our cells) has been shown to be quite low in early studies which may be due to its low absorption and fast metabolism. More recent studies, however, have demonstrated that we can absorb significant amounts of quercetin from our food or supplements with different forms of quercetin being more bioavailable than others.

For example, quercetin glycosides found in onions and shallots have been found to be far better absorbed than quercetin compounds found in tea.

Another important finding is that when combined with other nutrients such as Vitamin C, folate and other flavonoids, quercetin becomes more bioavailable meaning more can reach cells to exert its therapeutic effects. As Naturopaths, we learn and practice ensuring the ….

Research surrounding the most bioavailable supplemental form of quercetin is ongoing with the Alpha-Glycosyl Isoquercitrin form found to be most bioavailable. This can be found only in some supplements.

After absorption in the small intestines, quercetin is metabolised in the colon, liver and kidneys one study found the highest concentration of metabolites in the lung, liver and kidneys in animal models. With the kidneys functioning as one of the largest organs of elimination, quercetin is excreted via the urine.

Quercetin as an anti-inflammatory

As I discussed earlier most of the benefits of quercetin is due to its powerful anti-inflammatory actions and this is shown in multiple studies in both human and animal models. These anti-inflammatory benefits can be found in many health conditions including obesity, type 2 diabetes, allergic rhinitis, arthritis, gout, autoimmunity, acute kidney injury and the list goes on!

Inflammation is a driver of disease and is a complex process as there are a variety of mechanisms contributing to changes in blood flow and the release of several chemicals (mediators) within the body.

One well-known mechanism is the cyclooxyrgenase (COX) and lipooxygenase (LOX) pathway which once active, enzymes produce an inflammatory cascade of chemicals that are significant drivers of inflammation and disease.

Quercetin has demonstrated inhibitory activity on the COX-2 and LOX pathways helping to reduce inflammation and associated symptoms.

Reduction of other inflammatory chemicals including IL-1, IL-6, TNF, IL-8 has also been observed as well as inhibiting lipopolysaccharide (LPS) induced production of TNF and IL-8 which have direct effects on lung tissue and microglial cells in the brain.

The vast mechanisms by which quercetin is able to exert an anti-inflammatory effect within the body extends its benefits to a variety of health conditions and is an important compound to consider for an inflammatory condition!

Quercetin as an Antioxidant

The antioxidant effects of quercetin also help in the prevention and treatment of many common diseases and help to keep the balance between free radicals and antioxidants.

Oxidative stress occurs in everybody and refers to the production of reactive oxygen species. Issues only arise (which they commonly do) when the balance is out causing an excess of free radicals which can damage fatty tissue, DNA and proteins. Over time this damage can lead to chronic diseases including osteoporosis, diabetes, neurodegenerative disease and cardiovascular disease.

Quercetin has been used extensively in herbal medicine and Chinese medicine due to its antioxidant activity with research now being able to demonstrate its effects within the body.

The antioxidant activity of Quercetin is primarily due to its effect on

  • glutathione (GSH),
  • key enzyme activity,
  • impact on signalling pathways in the body and
  • balancing oxidative damage caused by reactive oxidative species (ROS).

GSH is the body’s main antioxidant that we produce and is essential for reducing oxidative stress. Quercetin is able to increase the body’s antioxidant capacity by regulating and increasing the production of GSH within our body.

Quercetin has also been shown to enhance the levels of other antioxidant enzymes in the body (CAT, MnSOD)  offering further protective effects from oxidative damage.

One of the most versatile functions of quercetin is its effects on different pathways in the body….it can up-regulate, activate, down-regulate and inhibit different processes. Having this ability allows quercetin to improve the overall state of the body and help to repair injuries which scientific studies now has shown in atherosclerosis, spinal cord injury and heavy metal toxicity. 

Quercetin in Kidney health

There have been several studies demonstrating the effectiveness of Quercetin in kidney health and its protective benefits which are mostly due to its powerful antioxidant and anti-inflammatory actions we have just discussed.

Over recent years a number of scientific studies in animal models have shown significant renal protective effects of quercetin against nephrotoxic agents including heavy metals (eg. cadmium, mercury) and pharmaceutical medications (eg. methotrexate, cisplatin, Ciprofloxacin)

Some of the therapeutic benefits from treatment with Quercetin included:

– reduction of tubular, degeneration, dilation and atrophy

– maintained renal blood flow, BUN and Creatine levels

– decrease the accumulation of heavy metals in the kidney

– reduction of kidney cell death

Research involving acute kidney injury and quercetin has again highlighted its protective effects on kidney function. The effects are thought to be due to the direct reduction of oxidative stress and inflammation with results showing a decrease in inflammatory chemicals iNOS and IL-12 and regulating renal function and BUN and creatinine levels.

The protective effect of Quercetin also extends to helping to block or stop kidney lesions or dysfunction which can be caused by a viral infection, sepsis, diabetic nephropathy or ischemia (lack of oxygen). 

https://pubmed.ncbi.nlm.nih.gov/33297540/#&gid=article-figures&pid=figure-1-uid-0

So let’s look at the other benefits of Quercetin…..

Aside from its well-documented benefits for kidney health, we have already learnt so far that quercetin can be helpful in many other conditions and diseases.

Cardiovascular disease is a chronic condition that Quercetin has been found to have protective effects, especially in hypertension. Flavonoids are powerful antioxidants (as we know!) however they also have vasodilatory actions which can assist with hypertension. Vascular and endothelium dysfunction are markers in cardiovascular conditions and with the antioxidant and vasodilator benefits of quercetin, the future research into quercetin benefits is exciting!

Allergies are also a common chronic condition and I am sure we all know at least one person with an allergy.  Due to its effect on immune cells and ability to stabilise mast cells (these cells release histamine and other chemicals), quercetin has been shown in studies and in clinical practice to help with reducing symptoms of allergy and inflammation.

So how much Quercetin do we need?

It is estimated that the average daily intake of quercetin is between 3-40 mg per day in typical western diets and up to 250mg per day for individuals who consume a higher plant-based diet, which has been shown in Japan.

In clinical practice, supplemental quercetin is prescribed between 300mg – 1200mg per day for therapeutic effects however this varies depending upon the specific health condition.

As with many other of our great nutrients, quercetin has a synergistic effect when combined with other nutrients which enhances its health benefits and effectiveness!

Well known synergistic nutrients when combined with Quercetin include:

  • Bromelain (found in pineapple)
  • Vitamin C
  • Green tea extract
  • Rutin (polyphenol)
  • Resveratrol
  • Folate

These synergistic combinations can often be found together in a formula for enhancing benefits.

When considering a diet, ensuring you are consuming a diverse range of plant-based foods is key to increasing intake of quercetin (and many other beneficial polyphenols) Not only are they rich in polyphenols but plant-based foods also contain other nutrients and compounds to further help with absorption and bioavailability.

Should you be cautious with Quercetin?

As with any medicinal product (herbal, nutritional or pharmacological), there may be a risk of side effects, especially if taken outside of the recommended dosage guidance.

Quercetin is generally very safe with no known severe side effects unless taken in large doses. This can include hypertension, hypokalaemia, headaches or ….. however, if you experience any changes it is recommended to follow up with your health care provider.

It is estimated that people who take supplements consume approximately 100 times more polyphenols than those commonly found in a Western-style diet therefore caution and guidance from a Health practitioner is always recommended.

Currently, there is insufficient evidence for the safety of quercetin in pregnancy and lactation therefore it is advised to avoid this as a supplement.

Potential interactions with pharmaceutical medications are always recommended to be assessed as there can be some contraindications.

Conclusion

Quercetin is a powerhouse flavonoid with its anti-inflammatory and anti-oxidant properties leading the way for its therapeutic benefits.

Quercetin already provides protective effects for many common health issues including chronic kidney disease of which it provides great benefit.

The future of Quercetin and its role in chronic health conditions is already evolving in research and it is exciting.

If you have been advised or are looking to decrease inflammation and improve health, quercetin is definitely a consideration and under the care of a good health care practitioner, may help to improve your health and quality of life.

Never underestimate the power of plant medicine. 

Research links

Lúcio Ricardo Leite Diniz , Marilia Trindade de Santana Souza , Allana Brunna Sucupira Duarte, Damião Pergentino de Sousa. Mechanistic Aspects and Therapeutic Potential of Quercetin against COVID-19-Associated Acute Kidney Injury. Molecules 2020, 25, 5772; doi:10.3390/molecules25235772

Susanne Andres, Sophie Pevny, Rainer Ziegenhagen, Nadiya Bakhiya, Bernd Scha ̈fer,* Karen Ildico Hirsch-Ernst, and Alfonso Lampen. Safety Aspects of the Use of Quercetin as a Dietary Supplement. Molecule Nutrition and Food Research. 2018, 62, 1700447

https://www.researchgate.net/profile/Karen-Hirsch-Ernst/publication/321014123_Safety_Aspects_of_the_Use_of_Quercetin_as_a_Dietary_Supplement/links/5c03d507a6fdcc1b8d502a93/Safety-Aspects-of-the-Use-of-Quercetin-as-a-Dietary-Supplement.pdf

Xu D, Hu MJ, Wang YQ, Cui YL. Antioxidant activities of quercetin and its complexes for medicinal application. Molecules. 2019. doi:10.3390/molecules24061123

Yao Li Jiaying Yao, Chunyan Han, Jiaxin Yang, Maria Tabassum Chaudhry, Shengnan Wang, Hongnan Liu, Yulong Yin. Quercetin, Inflammation and Immunity Nutrients 2016, 8, 167; doi:10.3390/nu8030167 https://ndnr.com/autoimmuneallergy-medicine/enhancing-bioavailability-of-quercetin/

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