Quercetin: Benefits, side-effects, research

Quercetin, a naturally occurring compound, has caught the attention of health enthusiasts worldwide. 

Found abundantly in foods like apples and onions, this flavonoid boasts potential health benefits that many are keen to explore. 

From traditional medicine to modern research, quercetin’s role in promoting wellness remains a topic of interest. 

This article aims to provide a comprehensive overview of quercetin, highlighting its sources, benefits, research, and more.

What is quercetin?

Quercetin is a natural compound classified as a flavonoid. These flavonoids are pigments that give many fruits, vegetables, and flowers their colors. Apart from adding vibrancy to our foods, quercetin offers a range of potential health benefits. 

Many studies suggest that it can act as an antioxidant, combating free radicals that can damage our body’s cells [1]. 

Some people turn to quercetin for its anti-inflammatory effects, which might help alleviate symptoms of conditions like allergies. Apples, onions, berries, and even tea contain significant amounts of this flavonoid. 

As interest grows, more individuals seek to understand and harness its potential benefits for health and well-being. 

While nature generously provides quercetin in various foods, it’s also available as a dietary supplement for those seeking concentrated doses.

Health benefits of quercetin

Health benefits of quercetin

Quercetin, a natural flavonoid found in various fruits, vegetables, and plants, has piqued the interest of researchers and health enthusiasts alike due to its potential health benefits. Here’s a look at some of the key advantages associated with quercetin:

1. Neutralizes harmful free radicals

Quercetin acts as a robust antioxidant, meaning it can neutralize harmful free radicals. These unstable molecules, when left unchecked, can lead to cell damage, potentially contributing to aging and various diseases.

2. Soothes inflammation

Chronic inflammation has links to several health conditions ranging from arthritis to heart diseases. Quercetin offers anti-inflammatory properties [2] that can help soothe inflammation, providing relief to individuals suffering from related ailments.

3. Reduces allergy symptoms 

Allergies can be a significant concern for many. Quercetin might come to the rescue, acting as a natural antihistamine. It has the potential to reduce the release of histamines, chemicals in the body responsible for allergy symptoms such as itching, swelling, and sneezing.

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4. Enhances heart health

Cardiovascular health remains a top priority for many. Quercetin could play a role here, with studies suggesting it may help reduce blood pressure levels. Additionally, its antioxidant nature might protect against LDL cholesterol oxidation, a critical factor in heart disease development.

5. Boosts respiratory health

There’s growing evidence that quercetin might offer benefits for respiratory health. Some studies suggest it can help reduce symptoms associated with respiratory infections and even asthma.

6. Protects the brain

The brain, like any other organ, is susceptible to oxidative stress. Quercetin’s antioxidant properties might safeguard the brain, potentially reducing the risk of neurodegenerative diseases like Alzheimer’s.

7. Regulates blood sugar

Quercetin may benefit those monitoring their blood sugar. Preliminary research indicates that it might help improve glucose absorption and insulin regulation [3], crucial for individuals with diabetes or metabolic syndromes.

While the above benefits highlight quercetin’s potential, it’s important to exercise caution. Not all effects are guaranteed for every individual, and the body’s response can vary. 

Moreover, while many studies back the benefits listed, ongoing research continues to further our understanding of this flavonoid.

Those eager to tap into quercetin’s potential health benefits can consider integrating quercetin-rich foods into their diet, such as apples, onions, and capers. Alternatively, dietary supplements offer a more concentrated form of quercetin for those interested.

Natural sources of quercetin

Quercetin naturally thrives in various foods. Many of these sources are staples in everyday diets, making it relatively easy for individuals to incorporate quercetin into their meals. Here’s where you can find this flavonoid:

1. Apples

Often hailed for their health benefits, apples are a primary source of quercetin. Opting for the crunchy fruit, especially with its skin on, boosts your intake.

2. Onions

Especially red and yellow ones, these flavorful vegetables serve as a rich source, enhancing dishes while providing the benefits of quercetin.

3. Berries

Blueberries, raspberries, and blackberries, apart from their sweet taste, offer a good dose of quercetin.

4. Capers

Commonly used in Mediterranean dishes, capers pack a punch both in flavor and quercetin content.

5. Tea

Both green and black teas provide quercetin, making your daily cup even more beneficial.

How much quercetin should you take?

Understanding the right dosage is crucial when considering quercetin supplements. While this flavonoid naturally appears in many foods we consume, taking it in supplemental form requires more precision. Here’s what you should know:

General guidelines

Most studies examining the benefits of quercetin supplements have participants take doses ranging from 500 to 1000 mg per day [4]. It’s often divided into two administrations, like a split between morning and evening.

Factors affecting dosage

  • Purpose: The reason for taking quercetin plays a significant role in determining the dose. For instance, someone aiming to alleviate allergy symptoms might require a different dose than someone focusing on heart health.
  • Form: Quercetin supplements come in various forms, including capsules, powders, and liquid extracts. Each form might have a distinct concentration, influencing the ideal dosage.
  • Duration: Short-term use and long-term supplementation may have varying recommendations. Always monitor any changes in your body and adjust accordingly.

While quercetin boasts a good safety record, exceeding the recommended dose can lead to side effects such as headaches or tingling of the extremities.

Combining quercetin with certain medications might lead to interactions. It’s essential to discuss potential combinations with a healthcare provider.

Everyone’s body is unique, and reactions to supplements can vary. Hence, always consult with a healthcare professional before starting quercetin supplements. They can offer personalized advice tailored to individual health needs and goals.

Remember, while quercetin supplements offer a concentrated dose, obtaining quercetin from natural food sources is also beneficial. Balance is the key, to ensuring you harness the benefits without overdoing it.

Who should and should not take quercetin

Quercetin presents many potential health benefits. But like all dietary components, it might not be suitable for everyone. Let’s explore who might benefit most from quercetin, and for whom caution or avoidance might be advisable.

Who can benefit from quercetin?

1. Allergy sufferers

Quercetin acts as a natural antihistamine, helping to reduce allergy symptoms like sneezing, itching, and swelling [5]. Individuals tormented by seasonal allergies might find relief.

2. Athletes and fitness enthusiasts

Some studies suggest that quercetin can enhance athletic performance and muscle recovery. Thus, those involved in regular workouts might benefit.

3. People with inflammatory issues

Quercetin’s anti-inflammatory properties can soothe various conditions tied to inflammation, from arthritis to certain skin disorders.

4. Individuals seeking antioxidant support

For those looking to combat oxidative stress, which is linked to aging and several health issues, quercetin offers robust antioxidant properties.

Side effects and precautions when taking quercetin

Who should be cautious of quercetin?

1. Pregnant and breastfeeding women

There’s limited research on quercetin’s effects during pregnancy or lactation [6]. It’s always safer to consult a healthcare provider before introducing any supplement during these periods.

2. People on medication

Quercetin can interact with certain medications, including antibiotics and blood pressure drugs. If you’re on prescribed medication, it’s essential to discuss potential quercetin interactions with a doctor.

3. Those with kidney disorders

Excessive quercetin might affect kidney function. If you have any kidney-related issues, ensure you consult with a healthcare expert before starting a quercetin regimen.

4. People awaiting surgery

Quercetin might influence blood pressure and blood clotting. It’s wise to stop quercetin supplements a couple of weeks before any surgical procedure. Always inform your surgeon about any supplements you take.

Side effects and precautions when taking quercetin

When considering any supplement, awareness of potential side effects and precautions is essential. Quercetin, while natural and often beneficial, isn’t exempt from this rule. Here’s what you need to know before adding it to your regimen:

Common side effects

  • Headaches: Some users report mild to moderate headaches after taking quercetin supplements, especially in higher doses.
  • Stomach discomfort: Digestive issues such as stomach cramps, bloating, or nausea might arise, especially when taken on an empty stomach.
  • Tingling sensation: A few people experience a tingling sensation in their extremities after quercetin intake.

Rare but serious side effects

  • Kidney damage: High amounts of quercetin, especially for prolonged periods, might affect kidney function. It’s vital to stick to recommended doses and consult with a healthcare provider if any unusual symptoms appear.
  • Drug interactions: Quercetin can influence the effectiveness of certain medications, especially antibiotics and blood pressure drugs. Ensure you discuss with a doctor if you’re on any medications.

Precautions to consider

  • Dose matters: Overdoing it can lead to problems. Always adhere to recommended dosages or the advice of your healthcare professional.
  • Timing: Consuming quercetin with meals might reduce the risk of stomach discomfort.
  • Pregnancy and breastfeeding: Due to limited research on quercetin during pregnancy or lactation, always consult with a healthcare provider before taking any supplement during these times.

Upcoming surgery: Since quercetin can affect blood pressure and clotting, consider pausing its intake a few weeks before any planned surgery. Inform your healthcare team about all the supplements you’re taking.

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Recent research on quercetin

Several studies have shown the effects of quercetin on several illnesses and conditions. Here are some examples of quercetin’s effects: 

Diabetes

Studies [7,8] have shown that quercetin is a promising drug in treating diabetes. It improves plasma insulin levels while reducing blood glucose levels. 

In addition, also maintains the function and number of beta-cells in the pancreas responsible for producing insulin. It also decreases oxidative stress, which delays the progression of diabetes and its complications. 

Further, the studies revealed that glucose uptake of cells in the body is increased when quercetin is taken. Through several mechanisms, quercetin can modulate free radicals and their effects on cells while increasing the insulin sensitivity of these cells.

Cardiovascular diseases 

Due to its anti-inflammatory effects, quercetin is also suggested to reduce the risk of cardiovascular diseases. 

A 10-week study published in the International Journal of Preventive Medicine [9] examined the effects of 500 mg of daily intake of quercetin on inflammatory biomarkers and cardiovascular risks of female patients with type 2 diabetes. 

Results of this study suggested that daily intake of quercetin for ten months decreased systolic blood pressure.

The results were significant, meaning the difference in the experimental group’s average systolic pressure was significantly lower compared with the group that only received placebo medicine. 

Further, high-density lipoprotein cholesterol and triglycerides were significantly lower in the experimental group than in the control group. 

High-density lipoprotein cholesterol and triglycerides have been implicated in developing cardiovascular diseases in patients with type 2 diabetes. 

The same study also reported that the experimental group significantly reduced inflammatory cells such as interleukin-6 and tumor necrosis factor-alpha. 

These inflammatory cells are known to increase the risk of cardiovascular diseases and complications in patients with type 2 diabetes. 

Lowering these inflammatory cells suggests that quercetin is anti-inflammatory and can be used as a supplement to prevent cardiovascular diseases.

Alzheimer’s disease 

Alzheimer’s disease is characterized by progressive cognitive impairment, memory loss and difficulties performing daily functions such as eating. Many patients with moderate to severe forms also have wandering behavior, further complicating their care. 

A study [10] revealed that quercetin is part of formulations for drugs for Alzheimer’s disease. Quercetin is used due to its ability to regulate apoptosis or cell death mechanisms and its neuroprotective effect against oxidative stress. 

Neuron longevity is crucial in delaying the progression or the onset of Alzheimer’s disease. Quercetin has been shown to promote the longevity of neurons while increasing the production of neurons.

Alzheimer's disease 

Arthritis

Arthritis is a common condition associated with swelling, redness, stiffness and joint pain. As a result, individuals who have arthritis have difficulties moving around. This condition is related to several environmental, genetic and hormonal factors. 

Treatment of arthritis includes surgery use of nonsteroidal anti-inflammatory drugs and steroids. 

However, when steroids are used for a long time to manage arthritis, this can result in fractures and osteoporosis. 

The use of NSAIDS can also result in renal damage and gastric ulcers. Chronic inflammation of the joints would require surgery called arthroplasty, where destroyed joints are replaced. 

Quercetin has been reported to reduce inflammation and pain associated with arthritis [11]. Hence, supplementation of quercetin can help reduce inflammation and pain in arthritis. 

Since quercetin can help promote longevity, supplementation with this antioxidant could also improve health span as individuals suffer from fewer or no chronic conditions.

Comparing forms of quercetin supplements

Choosing the right form of quercetin supplementation can be a pivotal decision for many, given the variety available in the market. Let’s break down the most common forms to help make an informed choice:

Capsules and tablets

  • Pros: Offer precision in dosage and are convenient for daily intake.
  • Cons: Some might contain fillers or binders, and the body may not always absorb them efficiently.

Powders

  • Pros: Allow flexibility in dosage and can mix easily with drinks or foods.
  • Cons: Measurement might require more care to ensure the correct dosage, and taste can sometimes be a deterrent for some.

Liquid extracts

  • Pros: Often provide rapid absorption and are easy to blend in beverages.
  • Cons: Might come with a shorter shelf life and can be more perishable than other forms.

Softgels

  • Pros: Enhance bioavailability, ensuring more efficient absorption in the body.
  • Cons: Could be slightly pricier than other forms.

While each form has its merits, individual preferences, lifestyle, and specific health goals will guide the best choice. It’s also wise to check for any added ingredients or preservatives.

Closing thoughts

Quercetin stands out as a naturally occurring powerhouse, offering a range of potential health benefits. From the food we eat to the supplements we choose, it can be a valuable addition to our wellness routine. 

But as with all things, balance and awareness are key. Always prioritize natural sources, be mindful of dosages, and consult with healthcare professionals when in doubt. 

Embracing quercetin in a holistic, informed manner can pave the way for enhanced well-being and vitality.

FAQs

What is quercetin used for?

Known for its antioxidant and anti-inflammatory properties, quercetin is commonly used to support cardiovascular health, combat allergies, and bolster overall immune function.

Is it safe to take quercetin daily?

Quercetin is generally considered safe when taken in recommended doses. However, as with any supplement, it’s essential to consult a medical professional before incorporating it daily into your routine.

Is quercetin safe for kidneys?

In moderate doses, quercetin is usually considered safe for most individuals, including those with kidney concerns. However, excessive intake over prolonged periods might pose risks, so those with kidney conditions should consult a healthcare professional before using quercetin supplements.

Does quercetin fight viruses?

Quercetin has demonstrated antiviral properties in various laboratory studies. However, more comprehensive research is needed to confirm its efficacy in combating human viruses.

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[1] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6470739/ 
[2] https://www.frontiersin.org/articles/10.3389/fimmu.2021.689044/full 
[3] https://www.sciencedirect.com/science/article/pii/S0753332221013470 
[4] https://www.drugs.com/npp/quercetin.html 
[5] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7227109/ 
[6] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9497971/ 
[7] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2992896/ 
[8] https://pubmed.ncbi.nlm.nih.gov/12927910/ 
[9] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3775217/ 
[10] https://pubmed.ncbi.nlm.nih.gov/18602817/ 
[11] https://pubmed.ncbi.nlm.nih.gov/29197723/

Photograph: Danijela Maksimovic/Shutterstock
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