What is Quercetin?
Quercetin is a type of plant pigment, known as a flavonoid, that is naturally present in a wide variety of foods, including apples, onions, berries, red wine, and green tea. It is recognized for its antioxidant and anti-inflammatory properties. Because of these characteristics, it is often sold as a dietary supplement and promoted for various health benefits, though scientific evidence supporting many of these claims in humans is still limited. The U.S. Food and Drug Administration (FDA) generally recognizes quercetin as safe (GRAS) when used as an ingredient in foods and beverages.
General Safety and Usage
For most healthy adults, quercetin supplements appear to be safe when taken orally for short durations. Certain amounts have been used safely for a limited time in studies. However, the long-term safety of taking higher amounts is not well-established. Common, mild side effects can include headaches and upset stomach. Tingling in the arms and legs has also been reported.
Key Groups Who Should Avoid or Be Cautious with Quercetin
Despite its general safety profile, several groups of people should avoid taking quercetin supplements due to potential risks and a lack of sufficient research.
Pregnant and Breastfeeding Individuals
There is not enough reliable information to know if quercetin supplements are safe to use when pregnant or breastfeeding. While consuming quercetin through food is considered safe, the concentrated amounts in supplements are a concern. Animal studies suggest that quercetin can cross the placenta and affect the fetus, though no birth defects were noted. Due to the lack of human safety data, experts advise against its use during pregnancy and lactation.
Individuals with Kidney Disease
People with a history of kidney disease or compromised kidney function should avoid quercetin supplements. Some reports suggest that high amounts of quercetin may cause kidney damage, and this risk may be elevated for those with pre-existing kidney problems. Pregnancy can also stress the kidneys, adding another reason for expectant mothers to avoid the supplement. While some studies suggest quercetin may have protective effects on the kidneys in certain contexts, these are not conclusive enough to recommend supplementation for those with kidney disease.
Children
There is insufficient evidence to recommend the use of quercetin supplements in children. Due to the lack of safety data in this population, it is best to avoid giving them quercetin supplements unless directed by a healthcare provider.
Cancer Patients
Individuals undergoing cancer treatment should speak with their oncologist before taking quercetin. Quercetin can interact with certain chemotherapy drugs. While some research suggests it might enhance the effects of drugs like doxorubicin and cisplatin, it could also interfere with others. There are also concerns from animal studies about a potential risk of tumor promotion in estrogen-dependent cancers, though this is not confirmed in humans. Given the complexity, medical supervision is essential.
Potential Medication Interactions
Quercetin can interact with various medications, which is a critical consideration for anyone taking prescription drugs. It can affect how the liver breaks down certain medicines by interacting with cytochrome P450 enzymes.
| Medication Class/Drug | Potential Interaction | Source(s) |
|---|---|---|
| Blood Thinners (Anticoagulants) | May increase the risk of bleeding when taken with drugs like warfarin (Coumadin), aspirin, or clopidogrel. | , |
| Blood Pressure Medications | Since quercetin may lower blood pressure, taking it with antihypertensive drugs could cause blood pressure to drop too low. | , |
| Antibiotics | Can interact with certain antibiotics, particularly quinolone antibiotics like ciprofloxacin. | , |
| Cyclosporine | Quercetin may affect how the body processes this immune-suppressing drug. | , |
| Digoxin | Co-administration of quercetin with this heart medication should be avoided. | |
| Medications Changed by the Liver | Can interfere with drugs metabolized by cytochrome P450 enzymes (e.g., CYP3A4, CYP2C19), potentially increasing side effects. | , |
Conclusion
While quercetin offers potential antioxidant and anti-inflammatory benefits and is safe for many when consumed in food, its use as a concentrated supplement requires caution. Individuals who are pregnant or breastfeeding, children, and people with kidney conditions should avoid quercetin supplements altogether due to a lack of safety information and potential risks. Furthermore, anyone taking prescription medications—especially blood thinners, blood pressure drugs, or chemotherapy—must consult with a healthcare provider before starting quercetin to prevent potentially harmful interactions. Responsible supplementation always begins with an informed conversation with a medical professional.
For more information on quercetin, you can visit WebMD.
Disclaimer: This information is for general knowledge and should not be taken as medical advice. Consult with a healthcare professional before starting any new supplement regimen.
