Despite being sometimes well-meaning, wellness influencers often miss the mark concerning the safety and efficacy of certain products or behaviors they tout on social media. While promotions for outright dangerous practices such as eating raw beef are fortunately fewer and further between, there's often still an overemphasis on unproven products or behaviors such as crystals, parasite cleanses and essential oils. 

There are also a host of dietary supplement recommendations - many of which are suggested because a micronutrient's natural form has proven healthful, even if its supplement form has not. Quercetin supplements are the latest example of this, with its global market reaching a staggering $1.2 billion in 2022, per one analysis, despite scientists having more questions than answers concerning its dosage safety and effectiveness.

"While there are many scientific studies assessing the benefits of quercetin as a supplement, very few are definitive and/or high quality," says Dr. Denise Millstine, a women's health specialist and director of the Mayo Clinic integrative medicine clinic in Arizona.

What is quercetin? 

Quercetin is a plant-based pigment compound within a family of similar compounds known as flavonoids. Flavonoids are distinct for contributing to the vibrant colors of many fruits, vegetables, flowers and other plants. These include blueberries, broccoli, plums, kale, bananas, cherries, ginkgo biloba, peaches, red peppers, mint, cocoa plants, cinnamon, celery, citrus fruits, tea leaves, many herbs and spices, and flowers such as magnolias and orchids. 

Quercetin, specifically, "is found naturally in many healthy, whole foods such as cranberries, dark-colored grapes, garlic, and apples if you eat the skins," says Millstine; with capers and red onions containing the highest concentration of quercetin among all fruits and vegetables. Despite having a bitter and unappetizing flavor, many recipes and wellness beverages call for various forms of quercetin as an ingredient because of its frequently touted health benefits. 

What is quercetin good for? 

When consumed naturally in fruits and vegetables, quercetin has some health advantages that are especially useful considering that the body doesn't produce the compound naturally, so obtaining it from dietary sources is required. 

The primary benefit of quercetin is that it's a powerful antioxidant and thereby protects the body from cell-damaging free radicals. Quercetin also has benefits related to improving allergies, high cholesterol, hypertension, and potentially reducing one's risk of developing heart disease, dementia and rheumatoid arthritis, per the Mount Sinai Health System in New York. 

"Small studies have also shown it can potentially lower blood sugar and reduce symptoms in prostate infections," says Millstine. "And some association studies - which do not prove cause and effect - have shown that (increased amounts of quercetin) in the diet may be associated with a lower risk of several cancers."

"We have also seen that higher quercetin intake is associated with lower risks of cognitive decline and other health problems," says Dr. Walter Willett, a physician and professor of epidemiology and nutrition at Harvard T. H. Chan School of Public Health. But he adds that "we can't be confident that quercetin itself is the cause of the benefits we see from eating (quercetin-containing) foods as this could be the combination of other beneficial substances in these foods."

Is quercetin OK to take as a supplement? 

In addition to its natural form as found in many different foods, quercetin is also available as a dietary supplement in powder, pill and liquid form. "Chemically, the supplemental form of quercetin is the same as in foods, but it can be more concentrated in higher amounts and separated from other potentially beneficial effects in these foods," says Willett. 

And while the supplement form of quercetin has well-demonstrated tolerability and has received the U.S. Food & Drug Administration's Generally Recognized As Safe (GRAS) status for use as a dietary supplement, Millstine says it's supplement form may not be as well absorbed as its natural form, and that it is not regulated the same way food and drugs are.

It's also important to note that quercetin supplement dosage recommendations vary widely across different brands and forms, "and very high doses of it appear to be toxic, especially to the kidneys," says Millstine. She also warns that its supplement form "has the potential to interfere with other medications." Some individuals may also experience allergic reactions or gastrointestinal discomfort from taking it.

"Quercetin is definitely a biologically active compound, but I don’t recommend taking it as a supplement because we are not confident that it is specifically responsible for the benefits we see from eating fruits and vegetables that contain quercetin, or that there are not adverse side effects from taking high amounts in supplemental form," says Willett. "Instead, I suggest eating generous amounts of fruits and vegetables as health scientists continue our research on quercetin and other flavonoids."