Quercetin is a plant pigment (flavonoid) that people sometimes take as a medicine.
It is found in many plants and foods. Most studies look at the impact of flavonoids like quercetin within the diet rather than as a supplement.
Why do people take quercetin?
People take quercetin to try to manage a variety of issues, including:
- Heart and vessel problems
- Lowering blood pressure
- Prostate infections
- Preventing upper respiratory infections
- Disease prevention
Early quercetin research on heart and vessel disease is mixed. Some study results are positive but some are open to debate. For example, researchers link eating lots of foods high in quercetin to a lower risk of heart-related death in older men. But other studies are less convincing.
Some research suggests that oral doses of quercetin may decrease pain from prostate infections.
Some athletes try to increase endurance and improve athletic performance by using quercetin. Although animal studies are promising, the effects in humans, if any, are likely small. One of the biggest benefits to athletes taking quercetin is in protection from URI after intense workouts.
Some studies link a diet high in quercetin with a lowered risk of cancer. But more research is needed. Cancer research in animal models has been promising, but has not yet panned out for human trials. The latest meta-analysis looks at ovarian cancer and shows no detectable benefit.
And some research indicates that quercetin may have some ability to help prevent diseases, such as cancer and heart disease, and reducing choronic inflammation. Research suggests it does this by preventing harmful cells from building up in the body.
In general, much of the research on quercetin has been in animals or in cell cultures. More study is needed to prove quercetin's benefits and safety in humans, especially when taken as a supplement instead of in food.
Common oral dosages are 500 milligrams twice a day. People have also used lower dosages as well. However, optimal doses of quercetin have not been established for any condition. Quality and active ingredients in supplements may vary widely from maker to maker. This makes it hard to establish a standard dose.
Can you get quercetin naturally from foods?
Quercetin is abundant in nature and foods. People typically get between 5 and 40 milligrams a day from food. But if you eat lots of fruits and vegetables, you can get as much as 500 milligrams daily.
For example, think "quercetin" the next time you pour a glass of red wine, bite into a crunchy apple, treat yourself to some berries, flip a buckwheat pancake, slice an onion, or sip a cup of green tea. Other vegetables that have high amounts of quercetin include:
- Raw Asparagus
- Raw red onion
- Nuts and seeds
- Olive oil
- Red grapes
Quercetin is also in herbs such as:
- American elder
- St. John's wort
- Ginkgo biloba
What are the risks of taking quercetin?
When you take it as a food, quercetin is likely safe. As a supplement, quercetin may be safe if you take reasonable amounts for a short time, such as 500 milligrams twice a day for 12 weeks. Taken longer, the risks are unknown.
Side effects. Quercetin may cause headache or tingling in arms and legs. Other side effects may occur if you receive quercetin treatment by IV (intravenously).
Interactions. Be careful if you are taking drugs such as antibiotics, cyclosporine, warfarin, or drugs that are changed by the liver. Quercetin may change how these drugs work and raise the risk of side effects.
There don't appear to be interactions between quercetin and foods or other herbs and supplements.
The FDA does not regulate supplements. Be sure to tell your doctor about any supplements you're taking, even if they're natural. That way, your doctor can check on any potential side effects or interactions with medications, foods, or other herbs and supplements. He or she can let you know if the supplement might raise your risks.