The 18th and 19th centuries in England were, for the most part, fairly prudish times. If passionate young people wanted to express their feelings for one another, they couldn’t just make a playlist or respond to text messages with heart emojis. Instead, they resorted to floriography or the language of flowers. A rose wasn’t just a rose: A red rose signified passion; a pink one said, “Meh;” a white rose warned, “I’m going to stay pure, so watch it, buddy;” and a yellow rose promised undying friendship.
Plants communicate with us and the world using the language of color as well. While they don’t share romantic sentiments (as far as we know — although I’ve known some blackberry brambles that could get quite handsy), they do give us clues as to their healing powers.
The compounds in plants that enable them to send such signals are called polyphenols. There are over 8,000 of them (at least that we know of), and they belong to a few distinct families. The largest of these families, with over 6,000 compounds (and counting), is flavonoids.
(If you’re eager to read a big honking article all about flavonoids and why they’re so good for you, click here.)
One of the most commonly consumed flavonoids is called quercetin. It’s also one of the most studied. And it’s often touted as a nutrient that can play a big role in the prevention and treatment of heart disease. But what does science say about quercetin? How does it work in the body? Does it have other health benefits aside from cardiovascular? What foods are the best sources? And do you need to supplement to get enough?
Let’s explore the mysterious world of quercetin, and find out all the ways this powerhouse compound is trying to express its love.
What Is Quercetin?
Quercetin is a proud member of the flavonoid family of polyphenols — a class of phytonutrients produced by plants to help them resist fungi, bacteria, and other infections, as well as deter consumption by insects and animals. Quercetin comes in several forms, and one of the most famous among them is rutin.
Rutin has antioxidant and anti-inflammatory effects, and provides some protection against cancer and other diseases. It’s found in high concentrations in buckwheat, and in ginkgo, apples, and other fruits and vegetables.
Rutin, like almost all forms of quercetin, acts as an antioxidant in the body, helping protect you from disease, much like it protects plants from bugs and harmful bacteria. In your body, antioxidants help regulate oxidative stress pathways, preventing and repairing cellular and DNA damage.
Quercetin Health Benefits
Quercetin works on so many systems in the body that it’s no surprise it appears useful in preventing and treating a wide range of conditions. It’s usually easiest for researchers to study a compound when given as a supplement because food comes with a myriad of synergistic variables (such as antioxidants, fiber, calories, and other nutrients) that can impact results. So, most of the research on quercetin has involved supplemental forms. However, keep in mind that, as with most nutrients, food forms are probably best. Here are a few health benefits of quercetin that have been solidly backed up by scientific research (many involving supplementation, for the purposes of the studies).
Quercetin and Heart Health
Quercetin has shown impressive cardiovascular effects in animal and test-tube studies. It lowers blood pressure, reduces cholesterol levels, improves glucose control, prevents the buildup of plaque in arteries, and protects the heart from damage. Clinical trials in humans have found that quercetin can contribute to healthier cholesterol numbers.
A 2016 meta-analysis of seven small controlled clinical trials (with a total of under 600 participants) found a reduction of both systolic and diastolic blood pressure with quercetin supplementation of more than 500 milligrams per day.
One way quercetin can support your heart is by protecting one of the cardiovascular system’s “weakest links:” the endothelial lining of your blood vessels. The endothelium performs a host of essential functions, including helping control the width of your blood vessels and playing a role in blood clotting, inflammation, and immune responses. As it ages, it tends to wear out, and modern drugs and surgical techniques haven’t been able to extend its working life.
Quercetin, on the other hand, appears to protect the endothelium from damage, and in doing so, could help to prevent certain types of heart disease.
Quercetin for COVID-19
Quercetin is known for its antimicrobial, antiviral, anti-inflammatory, antioxidant, and other beneficial effects in the fight against SARS, a coronavirus in the same family as COVID-19. That’s why scientists have had high hopes for the flavonoid as a means of preventing and treating COVID-19.
Researchers in 2022 found that quercetin did indeed inhibit three parts of the coronavirus cycle of infection: entry, absorption, and penetration. They suggested that it might work synergistically with vitamins C, D, and E as well as other polyphenols as a first-line prevention and treatment protocol for the novel coronavirus.
This was put to the test in a study published in early 2023, in which 50 patients with COVID-19 were given either standard of care or standard of care plus 500 milligrams of quercetin per day. The quercetin group had fewer symptoms than the control group, recovered faster, and tested negative sooner as well.
Some researchers and clinicians are starting to include quercetin in “inventive” drug compositions designed to treat COVID-19, pairing it with vitamins, other phytonutrients, and mainstream pharmaceuticals like Paxlovid.
Quercetin and Cancer
Quercetin appears to disrupt the progression of some cancers, particularly those of the gastrointestinal system, by pushing cancerous cells to self-destruct (a process known as apoptosis). It can also arrest the cycle through which the cancer cells divide and proliferate, as well as inhibit angiogenesis, which is the creation of new blood vessels in a growing tumor.
And that’s just scratching the surface of the ways quercetin appears to mess with cancer. Recently, researchers have been exploring the use of quercetin as an ingredient in “chemoprevention” cocktails that aim to stop cancer before it turns into a clinically significant disease. Preliminary studies have shown that quercetin is lethal to ovarian cancer cells at doses well within the range considered to be safe for daily consumption.
Quercetin for Inflammation
One of the most significant risk factors in the development of cardiovascular disease and type 2 diabetes is obesity. But why? What’s the connection?
Some researchers point to the fact that obesity causes chronic inflammation, particularly in the liver, fat cells, skeletal muscles, and circulatory system. Quercetin’s anti-inflammatory power can lessen insulin resistance (a key driver of type 2 diabetes) and combat atherosclerosis (a big component of heart disease). Also, quercetin helps gut microbiota stay healthy even when dealing with obesity-related inflammation.
A 2020 study found that treating skin cells with quercetin protected them against damage from the inflammation that accompanies skin conditions like atopic dermatitis. Quercetin increased levels of protective compounds (occludin and E-cadherin, if you’re into the details here) and reduced levels of harmful ones (matrix metalloproteinases, to be precise). What’s more, wounds treated with quercetin healed faster, due partly to an increased production of skin proteins and inhibition of the release of enzymes that can degrade skin tissue.
Quercetin’s anti-inflammatory properties suggest that it may also be a powerful booster of the immune system. But as careful scientists love to say, “More research is needed.”
Quercetin and Brain Health
Scientists are also hopeful about quercetin’s potential as a therapy to prevent the progression of neurodegenerative conditions such as Alzheimer’s. It may shield your brain cells from harmful effects caused by unstable molecules (there’s that antioxidant superpower again) while also reducing the breakdown of fats in the brain.
Quercetin also stops the buildup of specific harmful proteins, preventing cell destruction and what’s ominously known as inflammatory cascade pathways.
In addition to Alzheimer’s, other neurodegenerative diseases that are fueled by inflammation include Parkinson’s disease, multiple sclerosis, and amyotrophic lateral sclerosis (ALS). The inflammation in the brain among these disorders can lead to neuronal cell death, with devastating consequences for health, life span, and quality of life.
Recent research has uncovered a possible mechanism by which quercetin can put a stop to this inflammation — by influencing the expression of microRNA. MicroRNA is a small noncoding RNA molecule involved in various biological processes, including development, cell differentiation, and proliferation. Some researchers believe that quercetin’s ability to influence microRNA could be a powerful tool in preventing the damage that accompanies inflammation, and they’re exploring methods of delivering the nutrient in ways that increase its efficacy.
Your body can’t make its own quercetin, so the only way to take advantage of this amazing compound is to get it from food or supplements. If you’re eating a nutritionally excellent diet with a variety of whole plant foods, the good news is that you can expect to consume up to 13 milligrams of quercetin per day.
The less good news is that quercetin bioavailability is generally low. Or at least, humans don’t appear to be very good at absorbing it. All is not lost, though. It turns out that some of your gut microbes are very good at metabolizing quercetin into forms your body can use and benefit from.
There are several ways to increase the bioavailability of quercetin. A 2005 study measured the amount of quercetin in several onion cultivars that were either baked, sautéed, or boiled. Researchers found that baking and sautéing increased quercetin concentrations while boiling decreased them.
You can also absorb more quercetin if you pair quercetin-containing foods with a fat source. That’s because quercetin dissolves in fat, which is why it’s known as lipophilic. And having those foods along with sources of water-soluble fiber, such as pectin and soybeans, may also improve quercetin bioavailability.
Finally, quercetin is more bioavailable when consumed as part of a whole food. That is to say, your body appears to recognize it and know what to do with it when it is delivered in a familiar package, together with all the other phytonutrients contained in that food.
Food Sources of Quercetin
Should You Take Quercetin Supplements?
Since quercetin is in so many different plant foods, for most people, supplements are probably not necessary — especially since whole-food sources appear to be more bioavailable.
There might be some instances, however, in which quercetin supplements could be beneficial. For someone suffering from chronic inflammation, supplemental quercetin may help. And studies have shown that it can inhibit histamine production and pro-inflammatory mediators, which could help allergy sufferers.
A 2016 study of rats who had had noxious chemicals sprayed into their nostrils found that supplementing at 25 milligrams per kilogram of body weight for at least five days reduced nasal rubbing and sneezing. (Our view on the use of animals in medical research is here.)
As we’ve seen, quercetin supplementation can reduce the length and seriousness of COVID-19, especially if administered at an early stage. It may also be able to improve performance and recovery in athletes, who seem to need more antioxidants than other people to counter the oxidative damage brought on by intense physical exertion.
In terms of safety, clinical trials of supplemental quercetin have shown no significant side effects with doses of up to 1,000 milligrams per day for up to 12 weeks. As quercetin isn’t very bioavailable to begin with, supplements often include another bioactive compound that can help with absorbability. Quercetin may be absorbed more effectively when combined with bromelain, zinc, and/or vitamin C.
Side Effects of Quercetin Supplements
The most common side effects of quercetin supplements are headache and upset stomach.
In terms of drug interactions — quercetin can impact how the body responds to certain medications, including blood thinners, antibiotics, and other drugs with a similar chemical structure. Quercetin may also interact with chemotherapy drugs used to treat cancer. Whether it improves their effectiveness or gets in their way is still up for debate.
And in female rats with estrogen-induced breast cancer, even dietary quercetin was problematic, as it increased tumor severity. However, it remains to be seen whether the same can be said for humans.
Since studies show that quercetin can significantly lower blood pressure and may protect cardiovascular health, it may enhance the effects of blood pressure and blood-thinning medications. Therefore, it’s probably best to talk with your health care provider before starting quercetin supplementation if you’re taking these types of medications.
Recipes with Quercetin
From delightful salads featuring quercetin-packed blueberries to a hearty dish that incorporates quercetin-rich artichokes, these recipes provide delicious ideas for how to enjoy everyday quercetin-filled foods. Enjoy the healing benefits of quercetin to help nourish your heart health, immune system, brain function, and more — all while indulging in plenty of delicious whole food, plant-based ingredients!
Indulge in our Cinnamon Apple Breakfast Smoothie, a delightful morning treat that not only tantalizes your taste buds but will also boost your day with quercetin and other vital nutrients. At the heart of this smoothie lies the unassuming apple, packed with quercetin, a potent flavonoid renowned for its antioxidant prowess. By including an apple in your smoothie, you’re also inviting the goodness of quercetin to join the party, enhancing both flavor and nutrition.
We just love how The Shine Brightly Salad can’t help but put a smile on people’s faces. The addition of sweet and juicy blueberries is one big reason why! Blueberries are bursting with quercetin, which is your ally in the fight against oxidative stress and inflammation. Plus, when combined with fresh leafy greens and toasty sunflower seeds, you’ll enjoy a fresh and vibrant salad that will help you shine from the inside out!
Artichokes are among the top quercetin-rich veggies — and boy, oh boy, do we love them (and hope you do, too!). This Cheesy Artichoke and Asparagus Penne is loaded with powerful antioxidants, phytochemicals, and essential minerals like magnesium, potassium, niacin, and folate. Adding artichokes to your diet regularly is a great way to lower inflammation and increase healing through plant power. What’s more, this colorful pasta has tons of fiber from the veggies, whole grains, and lentils, as well as protein from the lentils — so you’ve got the complete package when it comes to this meal.
Embrace the Power of Quercetin
Quercetin, a compound found in some of our most popular fruits and vegetables, is a powerhouse of nutritional goodness. Thanks to its antioxidant, anti-inflammatory, and immune-boosting abilities, it appears to be something of a dietary medicine cabinet in a single nutrient.
Some people, such as athletes and those suffering from respiratory illnesses like COVID-19, may benefit from supplementation. But for most people, eating a varied and balanced diet will allow you to get the quercetin (and other phytonutrients and antioxidants) you need to optimize your health.
Tell us in the comments:
- Which colors of the “food rainbow” do you want to eat more often?
- What are your favorite quercetin-containing foods?
- Which quercetin-rich recipe will you try next?
Featured Image: iStock.com/Marko Jan
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