What is quercetin and how does it work?

Quercetin is a plant flavonol which is one of six subclasses of flavonoid compounds. Flavonoids are compounds that are found in plants. These plant compounds have many health benefits when consumed. They have antioxidant, anti-inflammatory, and anti-carcinogenic activity. Flavonoids can help in the prevention of various chronic diseases including cardiovascular disease, Alzheimer’s, and atherosclerosis (buildup of plaque in arteries).

Quercetin is part of one of the subclasses of flavonoids, flavonols. Flavonols are found in many fruits and vegetables as well as tea and red wine. Flavonols have strong antioxidant activity and can reduce the risk of vascular disease (relating to blood vessels).

Quercetin is a powerful antioxidant and anti-inflammatory agent. Quercetin helps neutralize reactive oxygen species (also called ROS). ROS cause damage in cells. In addition, studies have shown that it has other health benefits and can protect against diseases like osteoporosis, certain forms of cancer, lung and heart diseases, and can even help with aging.

Does quercetin have high bioavailability?

One of the biggest things to consider when looking at plant compounds is whether or not they are bioavailable. What does this mean? Well, just because quercetin is found in lots of fruits and vegetables, it doesn’t mean that our bodies can absorb it. Bioavailability refers to the portion of a substance (in our case, quercetin) that enters into circulation and is able to have an effect on our bodies when consumed. This is a really important concept because if we are consuming a lot of something, but aren’t actually absorbing the bioactive compounds, then we would have to eat a lot of it to see or feel any benefits. 

The bioavailability of quercetin is somewhat dependent on the source. Foods that are higher in quercetin have better bioavailability and are better absorbed by our bodies. In general, quercetin is actually not very bioavailable meaning we do not absorb and use a lot of what we consume.

But, once we eat foods with quercetin, the quercetin is absorbed through our small intestine. From there it makes its way to various organs including our colon, liver and kidneys. Once the quercetin has reached some of our other organs, it is further metabolized (broken down) so that our body can begin to use it.

Now that we know how quercetin works, and its benefits, let’s talk about some of the foods that are high in quercetin.

Here are the top 10 foods that are high in quercetin.

1. Capers

 Capers are best known as small, little flower buds that are often pickled when consumed. They are native to various Mediterranean countries. Believe it or not, capers have the highest levels of naturally occurring quercetin of all foods. For every 100 grams of capers, you will be consuming 234 milligrams of quercetin. Even in its pickled form, as they are often consumed, capers still contain a considerable amount of quercetin.

2. Hot peppers

Fan of spicy foods? If you are then you might be glad to hear that hot peppers make the list. Both yellow and green hot peppers are high in quercetin with about 51 milligrams and 15 milligrams of quercetin per 100 grams of peppers respectively.

3. Herbs

Dill and cilantro are some of the best sources of quercetin. They contain 55 milligrams and 53 milligrams per 100 grams of the herbs respectively. While these herbs are great sources of quercetin, 100 grams is a lot of dill and cilantro. However, adding herbs to recipes is a great way to add flavour and sneak in a little quercetin!

4. Red onions

Onions have been used in traditional and folk medicine for centuries due to their wide range of health benefits. So, it comes as no surprise that onions, and red onions in particular, contain high levels of quercetin. Quercetin levels in various colours of onions have been studied. Red onions have the highest levels of quercetin followed by yellow onions and chartreuse onions. Additionally, the outer peel of red onions contains more quercetin than the inner peel!   

5. Asparagus

Asparagus is a spring vegetable that is abundant in quercetin. If you are Canadian (like us!), then you’ll be glad to hear that asparagus are available all year round. These vegetables are a great staple to add to your diet to increase your quercetin intake.

6. Cranberries (and a few other berries)

Cranberries are a great source of quercetin. Seen in their bright red colour, cranberries contain 15 milligrams of quercetin per 100 grams of cranberries. Other berries including blueberries, lingonberries and elderberries also contain high levels of quercetin!

7. Broccoli

Broccoli is a cruciferous vegetable. It is related to other vegetables like cabbage, kale and cauliflower. Broccoli is another source of quercetin, but did you know that the cooking method used can affect quercetin levels in this vegetable? The best way to ensure that your broccoli maintains its quercetin levels is by eating it raw, or by steaming it!

8. Kale

Looking for a way to spice up your salads? Try swapping lettuce for kale! While some lettuce contains low levels of quercetin, kale contains considerably more. In addition, kale is super rich in other nutrients such as vitamin A and vitamin K making it an incredible addition to your diet.

 9. Apples 

Apples are another great source of quercetin. Red and yellow apples such as red delicious, gala and golden delicious contain higher amounts of quercetin than green apples. Did you know almost all of the quercetin is found in the peel? That’s right! So make sure if you reach for an apple the skin stays on!

10. Tomatoes 

Tomatoes also contain quercetin, but again it is mainly in the skin! Approximately 98% of the quercetin found in tomatoes is found in the skin with the rest in the seeds and flesh. Tomatoes not only contain quercetin but are also high in another flavonol, kaempferol.

Other notable sources:

Some beverages are also sources of quercetin. These include red wine, tomato juice and various teas. Quercetin is also found in orange juice, white wine and coffee at lower concentrations.

Those foods not for you?

Don’t worry. There is another option – supplements! Quercetin supplements are available and provide an easy way to increase your quercetin intake. Our Quercetin supplement contains 500 milligrams of quercetin in an easy to take capsule! Just take one in the morning and one in the evening with food for your daily antioxidant boost.

The takeaway:

Quercetin is a plant flavonol. Flavonols are part of the flavonoid family which is a group of plant compounds with health benefits. Quercetin is a powerful antioxidant and anti-inflammatory agent. It can even help reduce the risk of various diseases including heart disease and some cancers.

Quercetin is found in many fruits and vegetables. It is highest in foods such as capers, hot peppers, red onion, berries, dark green cruciferous vegetables, apples, and citrus fruits. It can also be found in lower levels in various beverages. Alternatively, quercetin supplements are also on the market for those who do not consume high levels of quercetin through their diet. Supplements are a good alternative to increase quercetin consumption and boost the antioxidant activity in your body!

How will you incorporate more quercetin into your day-to-day life? Share your tips with us through our social media accounts (Facebook and Instagram)!

References

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5. Kwak, J.-H., Seo, J. M., Kim, N.-H., Arasu, M. V., Kim, S., Yoon, M. K., & Kim, S.-J. (2017). Variation of quercetin glycoside derivatives in three onion (Allium cepa L.) varieties. Saudi Journal of Biological Sciences, 24(6), 1387–1391.
6. Lakhanpal, P., & Rai, D. K. (2007). Quercetin: A Versatile Flavonoid. Internet Journal of Medical Update - EJOURNAL, 2(2).
7. Stewart, A. J., Bozonnet, S., Mullen, W., Jenkins, G. I., Lean, M. E. J., & Crozier, A. (2000). Occurrence of Flavonols in Tomatoes and Tomato-Based Products. Journal of Agricultural and Food Chemistry, 48(7), 2663–2669.