Even though wellness influencers often have good intentions, they can sometimes overlook the safety and effectiveness of certain products or behaviors they promote on social media. Luckily, there are fewer endorsements for extremely risky practices like consuming raw beef, but there is still a tendency to overly emphasize unverified products and practices such as crystals, parasite cleanses, and essential oils.

Many recommendations for dietary supplements also exist—often based on natural micronutrient forms that are known to be beneficial, rather than their supplement counterparts, which may not be as effective. A recent example is quercetin supplements, which reached a remarkable global market value of $1.2 billion in 2022, according to one analysis, even though scientists have more questions than answers regarding their safe dosage and efficacy.

“Although numerous scientific studies examine the benefits of quercetin as a supplement, very few are conclusive or of high quality,” notes Dr. Denise Millstine, a specialist in women’s health and the director of the integrative medicine clinic at the Mayo Clinic in Arizona.

What is quercetin?

Quercetin is a plant-based pigment and belongs to a group of compounds known as flavonoids. Flavonoids are recognized for the bright colors they impart to many fruits, vegetables, flowers, and plants, including berries, broccoli, plums, kale, bananas, cherries, ginkgo biloba, peaches, red peppers, mint, cocoa, cinnamon, celery, citrus fruits, tea leaves, various herbs and spices, as well as flowers like magnolias and orchids.

Quercetin is commonly found in many healthy, whole foods including cranberries, dark grapes, garlic, and the skins of apples,” explains Millstine, adding that capers and red onions contain the highest concentrations of quercetin compared to all other fruits and vegetables. Despite its bitter taste, various recipes and wellness drinks often include quercetin for its purported health advantages.

What are the benefits of quercetin?

When ingested naturally through fruits and vegetables, quercetin offers several health benefits, especially since the body doesn’t naturally produce it, necessitating its intake from food sources.

The main advantage of quercetin is its potent antioxidant properties, which help shield the body from damage caused by free radicals. Additionally, quercetin may help alleviate allergies, lower high cholesterol, manage hypertension, and potentially decrease the risk of heart disease, dementia, and rheumatoid arthritis, according to the Mount Sinai Health System in New York.

“Smaller studies have also suggested it might help lower blood sugar and relieve symptoms of prostate infections,” Millstine explains. “Some observational studies—which don’t establish cause-and-effect relationships—indicate that a higher dietary intake of quercetin may be associated with a reduced risk of several types of cancer.”

“We’ve also observed that greater quercetin consumption correlates with lower risks of cognitive decline and various other health issues,” states Dr. Walter Willett, an epidemiology and nutrition professor at the Harvard T.H. Chan School of Public Health. However, he cautions that “we cannot definitively say that quercetin causes the benefits derived from consuming foods rich in quercetin since it could be due to other beneficial substances found in these foods.”

Is it safe to take quercetin as a supplement?

In addition to being found naturally in various foods, quercetin is available as a dietary supplement in powdered, pill, and liquid forms. “Chemically, supplemental quercetin is identical to that found in food, but it can be more concentrated and separated from other beneficial substances in these foods,” explains Willett.

Although quercetin supplements have been shown to be generally well-tolerated and have received the U.S. Food & Drug Administration’s (FDA) Generally Recognized As Safe (GRAS) designation for dietary supplement use, Millstine mentions that its supplemental form may not be absorbed as well as the natural form and that it isn’t regulated like food and medicines.

It’s crucial to be aware that dosage recommendations for quercetin supplements vary significantly among different brands and forms, with very high doses potentially being harmful, particularly to the kidneys, cautions Millstine. She also highlights that these supplements “can interact with other medications,” and some individuals may experience allergic reactions or gastrointestinal side effects when taking them.

“Quercetin is undoubtedly a biologically active compound, but I don’t advise its use as a supplement.”

According to Willett, we cannot be certain that quercetin alone is responsible for the health benefits we gain from consuming fruits and vegetables that contain it, nor do we know if taking it in large supplements might cause harm. Therefore, I recommend that we focus on eating a wide variety of fruits and vegetables while researchers continue to investigate the effects of quercetin and other flavonoids.