Quercetin – Onion, fruits …

“Let food be thy medicine and medicine be thy food” – was expressed by Hippocrates more than 2000 years ago and the health benefits of natural food products have been considered for different goals since the ancient times.   What is Quercetin?

Image result for quercetin in food onions


Quercetin is a plant pigment (flavonoid). It is found in many plants and foods, such as red wine, onions, garlic, green tea, apples, berries, Ginkgo biloba, St. John’s wort, American elder, and others. Buckwheat tea has a large amount of quercetin.

People use quercetin also as a medicine. 


In collaboration with the UC San Diego Center for Integrative Nutrition, the Berry Good Food Foundation convenes a panel of experts to discuss the rise of comprehensive medicine and nutritional healing to treat chronic disease and maintain general well-being…



Speaking of garlic, people immediately think of it being nature’s antibiotics, it  is also rich in soluble fiber, minerals, and especially antioxidants, anti-aging and anti-inflammatory ingredients.  And, Quercetin in Vietnam Black Garlic is an indispensable active ingredient in this list, more about that later.

Various studies have been done about garlic:


Quercetin is found in many fruits and vegetables and is safe to consume. As a supplement, it appears to be generally safe with little to no side effects. In some instances, taking more than 1,000 mg of quercetin per day may cause mild symptoms like headaches, stomach aches, or tingling sensations 

Quercetin is contained in abundance in apples, honey, raspberries, onions, red  grapescherriescitrus fruits, and green leafy vegetables.   Among vegetables and fruits, quercetin  content is highest in onions. The bulb color and type seems to be a determining factor for quercetin concentration in onions.


Onions for example, are an overlooked vegetable.   Onions are most known for their pungent flavor, not necessarily their nutritional value.  A single serving of onions is considered to be one medium onion, which contains around 52 milligrams (mg) of quercetinQuercetin is one of the most studied dietary flavonoids and is associated with multiple health benefits. Two of this compound’s most notable benefits are supporting heart health and protecting against oxidative stress. 

Heart health: Quercetin plays a positive role in supporting healthy blood pressure and endothelial health. The endothelium is the thin layer of cells lining the body’s blood vessels and heart. It is considered an active organ in the body as it helps control when blood vessels relax or constrict.

Protection against oxidative stress: Everyone undergoes oxidative stress, which is caused when there is an imbalance of harmful free radicals, which damage cells and tissues. This process happens inside the body, so although you may not feel immediate effects from oxidative stress, it can affect both health and the immune system over time. Antioxidants can help quell some of that stress. And since quercetin acts as a free radical scavenger and supports antioxidant processes, it’s especially good at this.

Because these health benefits are mainly seen at higher levels of quercetin intake, it’s important to maximize what you can from the diet.

  1. Choose the right variety:    Quercetin is a major compound in all varieties of red onions and chartreuse onions.  All onions are healthful and are rich in antioxidants.
  2. Don’t overpeel:    Quercetin is unevenly distributed in onions and is more highly concentrated in the outer layers of the peel. So after you peel back that thin paper covering, the first two to three layers, which tend to be thicker and maybe even a little slimy, have the most quercetin. Don’t peel and discard those layers. Chop or slice them up with the rest of the onion. And it’s always a good idea to wash onions under cold water after peeling to get rid of any dirt or contaminants that may have slipped through the outermost layer.
  3. Cook without water or eat raw:   One study looked at the effect that various cooking methods have on flavonoid intake from an onion.  The results showed that frying onions with oil or butter did not affect quercetin intake status, microwave cooking without water better retained flavonoids than with water, and boiling onions resulted in in about a 30% loss of quercetin into the water. However, eating onions raw is the likely the best way to ensure the quercetin content remains at its peak at the time of ingestion. Try thinly slicing red onions and adding them to sandwiches and salads.



Studies at Wageningen Agricultural University, the Netherlands, showed that the absorption of quercetin from onions is twice that from tea and more than three times that from apples. 

Based on studies conducted at The Queen’s University at Belfast, Ireland and Wageningen Agricultural University, the content of quercetin in onions is estimated to be between 22.40 mg and 51.82 mg per medium-sized onion (100 grams). Further research at the Agricultural University of Wageningen showed that daily consumption of onions may result in increased accumulation of quercetin in the blood.   

This 2015 study, published in the British Journal of Nutrition, concluded that supplementation with 162 mg/d quercetin from onion skin extract lowers ambulatory blood pressure in patients with hypertension, suggesting a cardioprotective effect of quercetin.    This study found that onion had an anti-diabetic effect in animals and a blood sugar lowering effect in humans.     This study, published in April 2020 in the American Journal of Clinical Nutrition, found that a diet rich in flavonoids — commonly found in onions — can reduce the risk of developing Alzheimer’s Disease and related dementias.    A study published in August 2019 showed a clear link between the amount of onions and garlic consumption and the reduced risk of breast cancer.    Several studies have shown quercetin to have beneficial effects against many diseases and disorders including cataracts, cardiovascular disease as well as cancer of the breast, colon, ovarian, gastric, lung, and bladder.

  • High in Vitamin C, onions are a good source of dietary fiber, and folic acid.
  • They also contain calcium, iron, and have a high protein quality (ratio of mg amino acid/gram protein).
  • Onions are low in sodium and contain no fat.
  • Onions contain quercetin, a flavonoid (one category of antioxidant compounds).
  • Onions contain organosulfur compounds that may offer unique health benefits

Onion Health Research


Various studies done




Quercetin is a natural polyphenolic antioxidant, which is present in vegetables, fruits and juices.   All of these activities indicate that quercetin could be a compound with potential clinical application. 


Some fruits are commonly known for high levels of vitamin C and fiber. One serving provides about 10% of the daily value for vitamin C.   An apple or pear contains about 20% daily value for fiber for adults, while a peach or two apricots or two plums provide about 10% of the daily value for fiber. Apricots are also rich in vitamin A and carotenoids.  These fruits also contain phenolic compounds known as quercetin, with strong antioxidant properties. Red apples contain the largest amount of quercetin, with lesser amounts in yellow and green apples, peaches, pears and plums.

Click to access Apples%20pears%20peaches.pdf


Quercetin content in fruits and ratios to total flavonols and total flavonoids



Black garlic also contains nitrogen oxide, which has strong antiviral and antitumor effects. It also contains 2-linoleoyl-glycerol, an anti-inflammatory molecule.  Black garlic is rich in antioxidant and anti-inflammatory compounds, including Amadori/Heyns compounds formed during the Maillard reaction.

Black garlic

Black garlic was developed in the early 21st century in Korea, then Japan, and China. Today, black garlic is widely used and recognized after many published research showed its impressive nutritional properties. 

Linh Dan Vietnam Black Garlic is made by fermenting only fresh whole garlic in a temperature-controlled (65–80°C) and humidity-controlled environment for about 30 days, without using any additives or preservatives. After these garlic bulbs are removed from the heat, they are then oxidized in a clean room for another 45 days. This long process turn garlic cloves black and create a sweet taste. Many people believe that this taste will entice even those who don’t like to eat garlic. Compared to fresh garlic, black garlic has less allicin but double the concentration of antioxidants. During the fermentation process, it also produces melanoidin which is the substance that turn white garlic black.

Green Med Info has compiled a list of studies demonstrating the positive effects of garlic on 150 diseases which are classified into four main groups:

  • Anti-inflammatory (reduce the risk of osteoarthritis)..
  • Immune-boosting (antibacterial, antifungal, antiviral and antiparasitic).
  • Improving cardiovascular and circulatory health (anti-coagulation, prevent plaque, improve blood fat levels, lower bad cholesterol, lower blood pressure).
  • Protecting against 14 types of cancer cells (including brain, lung, breast and pancreatic cancer).



Afgesien dat waatlemoene baie voedsaam is, is dit ook ‘n vrug met vele gebruike.   Dit vertoon ook mooi saam met blomme en selfs groente rangskikkings by geleenthede. 

Waatlemoene – Watermelon – Hydroponic


Gebruik dit in jou guns en ook selfs vir beveiliging.  Prickley pears are easy growers and there are different ones.  Prickly pear cactus — or also known as nopal, opuntia and other names — is promoted for treating diabetes, and possible other diseases, such as high cholesterolobesity and hangovers.

Turksvye – Prickley pears


It is a good idea to fall back on vegetables and fruits owing to their many health benefits. And what better than beetroot and carrots along with some apples to boost your immunity system.

Healthy food – Gesonde voedsel


4 gedagtes oor “Quercetin – Onion, fruits …”

  1. […] “Let food be thy medicine and medicine be thy food” – was expressed by Hippocrates more than 2000 years ago and the health benefits of natural food products have been considered for different goals since the ancient times.   What is Quercetin?Quercetin  – Onion, fruits […]


  2. […] Onteiening ‘n tydbom – geen voedselFood and VitaminsNetherland – Food – farming – landZimbabwe – “bread basket” into a “basket case” ~~~ No farmer – No foodKiwi fruits – vrugteTurksvye – Prickley pearsQuercetin – Onion, fruits … […]


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