Have you heard of quercetin? This plant-based antioxidant offers nutritional support for allergy sufferers, in addition to promoting healthy aging.* But it is often overlooked.

In case you’re not familiar with this nutrient, we’ll explore what quercetin is, how it can benefit your health, and some foods high in quercetin.

What is quercetin?

Quercetin is a type of antioxidant known as a flavonoid (a fancy name for a plant pigment). This plant pigment contributes to the beautiful, vibrant colors of some of your favorite fruits and vegetables, many of which are foods high in quercetin.

Flavonoids protect your body against free radicals.* Free radicals are molecules with an unpaired electron. Free radicals will readily pair their extra electron either by donating it (called oxidation) or by accepting an electron from another substance (called reduction).

Although the production of free radicals is a normal part of our metabolism, free radicals in higher amounts can begin to harm our health. When there are too many free radicals – and not enough antioxidants like quercetin to neutralize them – it can throw the body out of balance, causing what is known as oxidative stress. Free radicals can attack the DNA, carbohydrates, proteins, and fats that are present in cells, and in doing so they damage these cells.

An excess of free radicals is linked to accelerated aging, an imbalanced inflammatory response, and various adverse health conditions. Likewise, a chronic state of oxidative stress can lead to numerous negative health conditions.1

How quercetin benefits your health

So, what role can quercetin play in your health? Similar to vitamin D, quercetin supports immune function.* Quercetin is most well-known for its strong antioxidant activity, its down-regulation of histamine production (which is helpful for individuals who suffer from seasonal allergies), and enhancement of blood vessel elasticity and blood flow.*

Eating foods high in quercetin or taking a quercetin supplement can also have a positive effect on maintaining a healthy inflammatory response by modulating the release of cytokines – molecules that help immune cells communicate with each other, thus coordinating the immune response.2*

Now that you know a bit more about quercetin, you might be wondering about food sources of quercetin. 

There are a lot of foods you might find on a quercetin food chart. To help you choose, here are three of the best foods rich in quercetin:

1. Capers

Referred to by some as a superfood, capers have the highest natural concentration of quercetin of all food sources.3 These edible flower buds, which are brined or pickled before eaten, are often used to prepare Mediterranean foods such as seafood, pasta sauces, and other dishes.

Researchers at the University of California’s Irvine School of Medicine found that quercetin in pickled capers can activate proteins needed for normal brain and heart activity. This includes heartbeat, muscular contraction, and the normal functioning of organs like the thyroid and pancreas.4 

As one of the foods highest in quercetin, consider incorporating capers into your diet by adding them to nutrient-rich salads, sprinkling them on top of a bagel with smoked salmon, or incorporating them into an antipasto platter or cheeseboard. Because they are often brined, capers are high in sodium; so if you are preparing a meal using capers, then either reduce or eliminate any added salt to balance out the saltiness of the dish to ensure you keep your sodium intake in check.

2. Apples

You know what they say – eat an apple a day. Apples are one of the most popular quercetin food sources, and they are very easy to incorporate into your diet. Several studies link quercetin in apples to supporting a reduced risk of numerous adverse health conditions.

For example, researchers in Finland looked at the association between dietary flavonoid intake and health. They studied 9,959 Finnish men and women ages 15-99 over the course of 24 years with a combination of examinations, questionnaires, and structured interviews.5 The researchers found an inverse relationship between flavonoid intake and chronic adverse health conditions and said this finding was “most likely attributable to the consumption of apples.” That’s not surprising when you see the most popular flavonoid sources consumed in this study – apples and onions, which accounted for 64 percent of total flavonoid intake. Out of the flavonoids, quercetin made up about 95 percent of the population’s total flavonoid intake in the study.5

3. Onions

Also on the list for foods with quercetin? Onions. When you prepare onions and chop them up, be mindful of what you discard because they might have an uneven distribution of quercetin. For example, red onions have a higher concentration of quercetin toward the outside rings and closest to the root.6

The way you cook your onions also matters for quercetin intake. One study, published in the Journal of Nutritional Science and Vitaminology analyzed the quercetin content in onions through three different cooking methods: frying, microwaving, and boiling. When frying the onions, researchers used three different frying methods – with corn oil, butter, or without oil for the control group. 7

Among the three various frying methods, researchers did not see a difference in quercetin content. Microwaving without water was more effective at retaining quercetin than with water. Finally, boiling was the least effective at retaining flavonoids with about 30 percent of quercetin being lost in the cooking process.7

A poorly absorbed nutrient

Although it's important to get enough natural sources of quercetin – just like any other nutrient – a key point worth mentioning is how well the human body naturally absorbs it. Because even if you’re eating foods high in quercetin, you might be falling short of the amount you need.  Unfortunately, only about 25 percent of ingested quercetin is absorbed into the bloodstream via from foods and supplements.8 

Although there are many quercetin-rich foods, absorption isn’t always equal; for example, the type of quercetin found in onions tends to be better absorbed than the type found in tea. In addition, quercetin is not soluble in cold water, and hot water only improves its solubility a little.2 Therefore, depending on what you eat and how you prepare quercetin foods, the bioavailability can vary.

However, there is good news. Researchers in Italy found that supplementing with quercetin that is complexed with phospholipids from sunflower oil (a complex known as a phytosome) demonstrates significantly greater absorption than non-complexed quercetin. They found that quercetin in this form was 20-times better absorbed than regular quercetin, resulting in a much greater blood level than quercetin not bound to a phospholipid.8

Bottom line – when supplementing with quercetin, it’s important to consider the source.

The takeaway

It’s important to get quercetin from a quality source. At Thorne, we want to ensure you get the most out of your daily supplement regimen. By formulating the quercetin used in Thorne supplements with phytosome technology, we optimize the nutrient’s absorbability.*

Consider Thorne’s Quercetin Phytosome, which is up to 20 times more absorbable than regular, unbound quercetin, for optimal benefit from a smaller amount.* The quercetin in Thorne’s quercetin phytosome supplements is extracted from Sophora japonica, also known as the Japanese pagoda tree. For healthy aging support, try ResveraCel®, which combines the bioavailability of quercetin phytosome with resveratrol and nicotinamide riboside to support the body’s natural aging processes and cellular metabolism.*

References

  1. Lobo V, Patil A, Phatak A, Chandra N. Free radicals, antioxidants and functional foods: Impact on human health. Pharmacogn Rev 2010;4(8):118-126.
  2. Chirumbolo S. The role of quercetin, flavonols and flavones in modulating . . . cell function. IADT 2010;9(4):263-285. doi:10.2174/187152810793358741
  3. Redford KE, Abbott GW. The ubiquitous flavonoid quercetin is an atypical KCNQ potassium channel activator. Commun Biol 2020;3(1):356. doi: 10.1038/s42003-020-1089-8. 
  4. Redford KE, Abbott GW. The ubiquitous flavonoid quercetin is an atypical KCNQ potassium channel activator. Commun Biol. 2020;3(1). doi:10.1038/s42003-020-1089-8
  5. Knekt P, Jarvinen R, Seppanen R, et al. Dietary flavonoids . . . . Am J Epidemiol 1997;146(3):223-230. doi:10.1093/oxfordjournals.aje.a009257
  6. Li Y, Yao J, Han C, et al. Quercetin . . . . Nutrients 2016;8(3). doi:10.3390/nu8030167
  7. Ioku K, Aoyama Y, Tokuno A, et al. Various cooking methods and the flavonoid content in onion. J Nutr Sci Vitaminol 2001;47(1):78-83. doi:10.3177/jnsv.47.78
  8. Riva A, Ronchi M, Petrangolini G, et al. Improved oral absorption of quercetin from Quercetin Phytosome®, a new delivery system based on food grade lecithin. Eur J Drug Metab Pharmacokinet 2019;44(2:169-177.