Quercetin is a type of plant pigment known as a flavonoid. It’s naturally found in a variety of foods and beverages.1 Quercetin is also available in supplement form.
Quercetin is an antioxidant and has anti-inflammatory effects that may help reduce swelling, regulate blood sugar levels, and prevent heart disease.1 Research shows that supplemental quercetin may also protect brain health, support immune function, and aid weight management.234
Dietary supplements are minimally regulated by the FDA and may or may not be suitable for you. The effects of supplements vary from person to person and depend on many variables, including type, dosage, frequency of use, and interactions with current medications. Please speak with your healthcare provider or pharmacist before starting any supplements.
Quercetin has been studied for a variety of conditions and has been shown to have an array of potential benefits, from aiding the immune system to reducing disease risk. Here are some of the main health benefits of quercetin:
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Has Antioxidant Effects
As a part of normal metabolism, the human body produces compounds called free radicals. Free radicals damage healthy cells, trigger gene mutations, accelerate aging, and increase the risk of various diseases, including heart disease and diabetes.5
Quercetin has been shown to counter the harmful effect of free radicals through its strong antioxidant activity. This antioxidant effect can help the body maintain a stable state, ward off premature aging, and reduce chronic disease risk. Much of this research has been done in cells or animals, but researchers suggest the effect is likely true for humans too.5
Has Antimicrobial Effects
Several studies have found that quercetin offers broad-spectrum antibacterial properties. Quercetin has been shown to protect against Salmonella enteritidis (salmonella), Staphylococcus aureus (staph), and Escherichia coli (E. coli) in part by destroying bacterial cell walls and changing cell function.5
Quercetin has also been shown to interfere with the growth of drug-resistant microorganisms. This means quercetin may help fight against strains of bacteria that don’t respond to treatment. Quercetin is particularly effective against bacteria that affect the skin, as well as the digestive, respiratory, and urinary systems. It’s also been shown to combat some viruses and fungi.6
Protects Heart Health
Quercetin guards heart health in several ways. It has been shown to reduce both systolic (the top number) and diastolic (the bottom number) blood pressure. Quercetin can also reduce the pressure on arteries.5 That’s important because, over time, high blood pressure can damage arteries and lead to heart disease.7
Quercetin has also been shown to curb total cholesterol and triglycerides.5 Triglycerides are a type of fat that, in high amounts, can increase your heart disease risk.8
Quercetin can also counter a process called oxidation, which changes “bad” low-density lipoprotein (LDL) cholesterol in ways that harden arteries.5
Quercetin can also help regenerate blood vessels to improve blood flow, which supports healthy heart function.5
May Help With Weight Management
Only a limited number of human studies have evaluated the effects of quercetin on obesity treatment, but the results are promising.
In one small study, six men and 30 women who were overweight or had obesity were randomly assigned to take either 100 milligrams (mg) of quercetin or a placebo every day for 12 weeks.
The researchers found that the quercetin group had significant decreases in weight; body mass index; and waist, hip, and thigh measurements. The quercetin group also had a reduction in overall body fat percentage, particularly in the arms.2
More research—especially in larger numbers—would be needed to say for certain the effect quercetin can have on weight loss or how quercetin would fit into an overall weight management plan.
May Protect Brain Health
Alzheimer’s disease is the most common cause of dementia among older adults. Over time, it destroys memory and thinking.9
Flavonoids, the family of antioxidants to which quercetin belongs, have been extensively studied for their antioxidant and anti-inflammatory activities—both of which are important in the prevention of Alzheimer’s.10 Research has shown that flavonoids as a whole may be able to help prevent the development or progression of Alzheimer’s.11
Research on how the flavonoid quercetin affects Alzheimer’s has been primarily animal-based. But one study in humans looked at the impact of quercetin-rich onion powder on cognitive function in 70 healthy Japanese adults aged 60-79. The participants were randomly assigned to consume either 11 grams of air-dried, high-quercetin onion powder or a placebo daily for 24 weeks.4
The results showed quercetin-rich onion powder may delay cognitive decline in older adults with early stage Alzheimer’s.4
The researchers also found the quercetin group experienced better cognitive function scores, improved depressive symptoms, and increased overall motivation.4
May Support Immune Function
Studies regarding quercetin and immune function have had mixed results, but there is some promise that the flavonoid can support immune function.
In one trial, 1,002 participants took 500 mg or 1,000 mg of quercetin or a placebo each day for 12 weeks. Overall, quercetin supplementation did not have a significant effect on rates of upper respiratory tract infections, such as colds, compared with the placebo.
However, in a subgroup of participants aged 40 or older who rated themselves as physically fit, 1,000 mg of quercetin per day resulted in fewer total sick days and a reduced severity of upper respiratory tract infection symptoms.3
Another small study among athletes found that supplementing with 100 mg of quercetin per day did not impact several measures of immune function after three days of intense exercise, but it did significantly reduce upper respiratory tract infection risk. In the two-week period after the exercise sessions, just one out of 20 participants in the quercetin group got sick compared to nine of 20 in the placebo group.12
May Help Improve COVID-19 Outcomes
There have been more than a dozen clinical trials to evaluate the effects of quercetin on the prevention and treatment of COVID‐19.13
One of those studies looked at the effect that a product made from quercetin and sunflower lecithin—which increases the rate of quercetin absorption by up to 20 times compared to pure quercetin—had on 152 people with COVID-19.14
Researchers found when the supplement was used in the early stage of COVID‐19 infection alongside conventional COVID‐19 therapies, patients had improvements in early symptoms and a reduced risk of severe COVID‐19 outcomes, including hospitalization.14
Still, more clinical trials are needed to firmly establish the effectiveness of quercetin supplements against COVID‐19.
The National Institutes of Health (NIH) included quercetin in its review of supplements for COVID-19. In that review, the NIH said that there wasn’t enough information to make a determination for or against the use of any supplement when preventing or treating COVID-19.14
May Aid in Autoimmune Conditions
Autoimmune diseases occur when the immune system mistakenly attacks your body’s healthy cells. Some of these conditions include rheumatoid arthritis (RA), inflammatory bowel disease, multiple sclerosis, and lupus.
Due to its protective anti-inflammatory and antioxidant abilities, quercetin may help prevent or manage autoimmune conditions.15
For example, in one small study, 50 women with RA were randomly assigned to receive either 500 mg of quercetin or a placebo every day for eight weeks. The quercetin group experienced significant reductions in early morning stiffness, morning pain, and post-activity pain compared with the placebo group.
In addition, the number of patients with active RA disease in the quercetin group significantly decreased.16
May Help Regulate Effects of PCOS
Polycystic ovary syndrome (PCOS) is a common cause of infertility, affecting 6%-12% of U.S. women of reproductive age. People with PCOS have higher levels of the male hormone androgen than people with female reproductive systems usually have. The levels of androgen can lead to several symptoms, including a stop in ovulation.17
People with PCOS are also often insulin resistant, which means their bodies make insulin but can’t use the insulin effectively. This can increase the risk of type 2 diabetes.17
A limited number of human studies have looked at the impact of quercetin supplements vs. a placebo on PCOS for up to 12 weeks. So far, the research has shown positive outcomes, with quercetin users experiencing improvements in both hormone and insulin regulation.18
However, scientists say there are not enough studies to make strong conclusions about the use of quercetin supplements for PCOS.18
Sources of Quercetin
While quercetin can be taken in supplement form, it is also naturally found in a variety of plant foods. Fruits, vegetables, herbs, and beverages are all potential sources of quercetin.
Here are examples of foods and drinks that might be good natural sources of quercetin:1920211
Fruits:
Vegetables:
Herbs:
- Chives
- Cilantro
- Dill
- Oregano
Beverages:
- Green tea
- Black tea
- Red wine
How To Take Quercetin
Queretin is taken in naturally through the food, drinks, and herbs you consume. If you are taking supplementary quercetin, it’s possible to use it topically, intravenously, and orally. Most people take quercetin orally, through a supplement capsule you’d buy at the store.22
Dosage
Tthere is no recommended daily quercetin intake for general health, wellness, or disease prevention. It’s typically used in doses of 250-1,000 mg daily for up to 12 weeks.22
Worth noting is that fruits and vegetables are the major sources of quercetin, and the 2020-2025 Dietary Guidelines for Americans advise adults to consume 1.5-2 cups of fruit and 2-3 cups of vegetables per day.23
It’s estimated that people take in anywhere from 50-800 mg of flavonoid antioxidants per day. It’s believed that quercetin accounts for 75% of that intake, depending on the consumption of fruits, vegetables, and tea.23
Is Quercetin Safe?
When used as an ingredient in food and drinks, quercetin is believed to be safe in amounts up to 500 mg per serving, according to the U.S. Food and Drug Administration (FDA).24
While you can also take quercetin in supplement form, the safety and effectiveness of long-term use hasn’t been well established. Currently, it is only known that up to 1 gram of quercetin supplements a day for 12 weeks has been considered safe. More research on longer use and higher doses is needed.1
People with kidney problems should avoid quercetin—especially when administered through the vein—since the supplement can make kidney issues worse. It’s unknown how safe quercetin is for people who are pregnant or breastfeeding, so these groups should also avoid the supplement.22
Potential Drug Interactions
Quercetin supplements may interact with some medications. For instance, quercetin might reduce blood pressure in people with high blood pressure, so the supplement could increase the effects of medications used to treat the condition, lowering blood pressure too much1
Quercetin might affect other medications, including Pravachol (pravastatin, used to treat high cholesterol) and Allegra (fexofenadine, an antihistamine used to manage allergy symptoms).1
Many of the studies on how quercetin interacts with other medications were done on animals or in test tubes. If you are taking any medication, talk with your healthcare provider about any potential risk there is before starting quercetin.22
What To Look For
As with any supplement, quercetin isn’t regulated by the FDA. To ensure what you are buying was manufactured correctly, is true to the ingredient list, and doesn’t contain harmful levels of contaminants, purchase a product that has been third-party tested. Reputable third-party testing organizations include ConsumerLab, NSF International, and U.S. Pharmacopeia.25
Can You Take Too Much Quercetin?
Kidney damage has been reported but only with the use of intravenous quercetin in large amounts. It’s unknown how safe large doses or long-term use of oral quercetin supplementation is.
Side Effects of Quercetin
Quercetin has not been shown to be toxic or to cause any serious side effects in any of the human clinical trials in which it’s been studied.15
Generally, quercetin is considered to be safe when gotten naturally through food and drinks.
While less is known about quercetin supplements, no serious side effects have been reported in clinical trials that used up to 1,000 mg a day for up to 12 weeks. One study that used 200 mg of quercetin twice daily for 30 days did show mild effects. These effects included stomach pain and reflux, constipation, diarrhea, gas, and sleep disorders. However, the rate of these effects was similar to that of the placebo group.24
A Quick Review
Quercetin, a plant pigment specifically known as a flavonoid, has antioxidant and anti-inflammatory effects. Research has shown that quercetin may help with a wide variety of issues, including Alzheimer’s disease, infections, and blood pressure. It is readily available in a variety of whole, plant-based foods and tea. You can also take quercetin in supplement form.
While quercetin supplements have been studied for certain medical conditions, there are currently no guidelines or recommendations for the use of these supplements for general health or disease prevention. If you are interested in taking quercetin, speak with your healthcare provider first to hear more about its potential benefits and side effects based on your specific health.
