Quercetin

Quercetin is a plant flavonol from the flavonoid group of polyphenols.

Updated: August 28, 2019

Quercetin is a plant flavonol from the flavonoid group of polyphenols. It is found in many fruits, vegetables, leaves, and grains. Although red onions and kale are common foods containing appreciable content of quercetin, it is also found in red wine, green tea, apples, berries, Ginkgo biloba, St. John's wort, American elder, and others. Buckwheat tea has a large amount of quercetin. Quercetin is present in various kinds of honey from different plant sources. Quercetin has a bitter flavor and is used as an ingredient in dietary supplements, beverages, and foods.
Quercetin is used as a medicine most commonly taken by mouth to treat conditions of the heart and blood vessels and prevent cancer. It is also used for arthritis, bladder infections, and diabetes. But there is limited scientific evidence to support these uses.
The antioxidant and anti-inflammatory properties of Quercetin help reduce inflammation, kill cancer cells, reduce allergy symptoms, control blood sugar, and help prevent heart disease. The antioxidants in it plays an important role in helping your body combat free radical damage, which is linked to chronic diseases. Antioxidants are compounds that can bind to and neutralize free radicals. Free radicals are unstable molecules that may cause cellular damage when their levels become too high. An average person consumes 10-100 mg of it daily through various food sources as it is abundantly available in various food. It is also available as a dietary supplement in powder and capsule form and can be taken as a dietary supplement for a variety of uses.

Dietary sources:

Quercetin is found naturally in many plant-based foods, particularly in the outer layer or peel.
Good food sources include:

  •     capers
  •     peppers; yellow and green
  •     onions; red and white
  •     shallots
  •     asparagus; cooked
  •     cherries
  •     tomatoes
  •     red apples
  •     red grapes
  •     broccoli
  •     kale
  •     red leaf lettuce
  •     all type of berries, such as cranberries, blueberries, and raspberries
  •     tea; green and black

Tthe amount of quercetin in foods may depend on the conditions in which the food was grown. For example, organic tomatoes have up to 79% more quercetin than commercially grown ones.

Uses & Effectiveness:

Possibly Ineffective for:

Athletic performance:

Taking quercetin before exercise does not decrease fatigue or improve exercise ability.

Alzheimer's disease and Dementia:

The antioxidant properties of quercetin may help protect against degenerative brain disorders, such as Alzheimer's disease and dementia. A quercetin-rich diet reduced markers of Alzheimer's disease and improved brain function. Quercetin is the primary compound in coffee that is responsible for its potential protective effects against this illness.

Insufficient Evidence for:

Heart disease:

Eating foods rich in quercetin, such as tea, onions and apples, may reduce the risk of death and complications due to heart disease in elderly men. However, taking a daily quercetin supplement does not seem to improve the risk factors of heart disease in people who are healthy.

Diabetes:

Taking a combination of quercetin, myricetin, and chlorogenic acid helps to lower blood sugar in people with diabetes who are not taking antidiabetes drugs. The same combination also seems to benefitial for those people with diabetes who are already taking metformin.

Muscle damage caused by exercise:

Taking quercetin doesn't seem to help to prevent muscle soreness due to cycling or running. But it might prevent muscle damage associated with certain types of weight training.

Airway infections caused by exercise:

Taking quercetin may reduce the chance for upper respiratory infections after heavy exercise.

Autism:

Taking a product containing quercetin and other ingredients might improve behavior and social interactions in children with autism.

Benign prostatic hyperplasia or BPH:

Taking a product containing quercetin, beta-sitosterol, and saw palmetto doesn't help with urination and other symptoms in men with BPH or enlarged prostate.

High cholesterol:

Short-term use of quercetin does not appear to lower 'bad cholesterol' (low-density lipoprotein (LDL) cholesterol) or total cholesterol, or to raise 'good cholesterol' (high-density lipoprotein (HDL) cholesterol). This is believed to be true for people without high cholesterol. It's unclear if quercetin would show benefit in only people with high cholesterol.

High blood pressure:

Taking quercetin helps reducing blood pressure in people with untreated, mild high blood pressure. It's unclear if this reduction in blood pressure is clinically meaningful.

Kidney transplant:

Early function of the transplanted kidney can be improved by taking a product containing quercetin and curcumin, starting within 24 hours of kidney transplantation, when taken in combination with anti-rejection drugs.

Lung cancer:

Higher intake of quercetin as part of the diet has been linked with a lower risk of lung cancer in people who smoke.

Oral mucositis:

Taking quercetin does not prevent mouth sores, swelling or inflammation caused by cancer drugs inside the mouth.

Ovarian cancer:

There is no link between quercetin intake from the diet and the chance of getting ovarian cancer.

Pancreatic cancer:

Eating high amounts of quercetin in the diet might reduce the chance of developing pancreatic cancer, especially in men who smoke.

Swelling (inflammation) of the prostate due to infection:

Taking quercetin by mouth seems to reduce pain and improve quality of life, but doesn't seem to help urination problems in men with ongoing prostate problems that aren't due to infection.

Polycystic ovary syndrome or PCOS:

PCOS is a hormonal disorder that causes enlarged ovaries with cysts. Taking quercetin improves hormone levels in women with PCOS by a small amount. In some people it might also improve how sensitive the body is to insulin. But it's unclear if these changes lead to improvements in symptoms of PCOS such as irregular periods.

Urethral syndrome:

Taking a product containing quercetin, bromelain, chondroitin sulfate, gotu kola, rhodiola, and barbed skullcap helps reduce how often people with urethral syndrome or painful urination due to swelling (inflammation) of the urethra need to urinate.

Urinary tract infections or UTIs:

Taking a combination of hyaluronic acid, chondroitin sulfate, curcumin, and quercetin by mouth, and applying estrogen to the vagina, helps to prevent UTIs that is infections of the kidney, bladder, or urethra in women who get them often. The quercetin product also works without the estrogen, but not as well.

Rheumatoid arthritis (RA):

Taking quercetin reduces pain and stiffness in women with RA. But it doesn't seem to reduce the number of swollen or tender joints.
More evidence is needed to rate quercetin for the below uses:

  •     Asthma.
  •     Cataracts.
  •     Chronic fatigue syndrome (CFS).
  •     Gout.
  •     "Hardening of the arteries" (atherosclerosis).
  •     Hay fever (allergic rhinitis).
  •     Pain and swelling (inflammation).
  •     Schizophrenia.
  •     Stomach and intestinal ulcers.
  •     Viral infections.
  •     Other conditions.

Side Effects & Safety:

Quercetin is possibly safe for most people when taken by mouth for short-term. Quercetin has been safely used in amounts up to 500 mg twice daily for 12 weeks. It is not known if long-term use or higher doses are safe. However, quercetin can cause headache and tingling of the arms and legs. Very high doses might cause kidney damage. Quercetin is possibly safe when given intravenously (by IV) in appropriate amounts which is less than 722 mg. Side effects may include flushing, sweating, difficulty breathing, nausea, vomiting or pain at the injection site. But larger amounts given by IV are possibly unsafe as it could lead to kidney damage.

Special Precautions & Warnings:

Pregnancy and breast-feeding :

There isn't enough reliable information to know if quercetin is safe to use when pregnant or breast-feeding. Stay on the safe side and avoid use.

Kidney problems :

Quercetin might make kidney problems worse. Don't use quercetin if you have kidney problems.

Interactions:

Be cautious with the below combination as these can have moderate Interaction:

Antibiotics (Quinolone antibiotics) interacts with Quercetin:

Taking quercetin along with some antibiotics might decrease the effectiveness of some antibiotics. Quercetin might prevent some antibiotics from killing bacteria. Ciprofloxacin (Cipro), enoxacin (Penetrex), trovafloxacin (Trovan), norfloxacin (Chibroxin, Noroxin), sparfloxacin (Zagam) and grepafloxacin (Raxar) are some of the antibiotics that might interact with quercetin.

Cyclosporin (Neoral, Sandimmune) interacts with Quercetin:

Cyclosporin (Neoral, Sandimmune) is changed and broken down by the liver. Quercetin might decrease how quickly the liver breaks down cyclosporin (Neoral, Sandimmune). Taking quercetin might increase the effects and side effects of this medication. Talk to your healthcare provider if you take cyclosporin (Neoral, Sandimmune) before taking quercetin.

Cytochrome P450 2C8 (CYP2C8) substrates interacts with Quercetin:

Some medications are changed and broken down by the liver. Quercetin might decrease how quickly the liver breaks down some medications. Taking quercetin along with these medications that are changed by the liver might increase the effects and side effects of your medication. Talk to your healthcare provider before taking quercetin if you take any medications that are changed by the liver.
Paclitaxel (Taxol), rosiglitazone (Avandia), repaglinide (Prandin), verapamil (Calan, Isoptin, Verelan), amiodarone (Cordarone), docetaxel (Taxotere) and others are some medications that are changed by the liver.

Cytochrome P450 2C9 (CYP2C9) substrates interacts with Quercetin:

Some medications are changed and broken down by the liver. Quercetin might decrease how quickly the liver breaks down some medications. Taking quercetin along with these medications that are changed by the liver might increase the effects and side effects of your medication. Talk to your healthcare provider before taking quercetin if you take any medications that are changed by the liver.
Celecoxib (Celebrex), diclofenac (Voltaren), fluvastatin (Lescol), glipizide (Glucotrol), ibuprofen (Advil, Motrin), irbesartan (Avapro), losartan (Cozaar), phenytoin (Dilantin), piroxicam (Feldene), tamoxifen (Nolvadex), tolbutamide (Tolinase), torsemide (Demadex), warfarin (Coumadin), and others are some medications that are changed by the liver.

Cytochrome P450 2D6 (CYP2D6) substrates interacts with Quercetin:

Some medications are changed and broken down by the liver. Quercetin might decrease how quickly the liver breaks down some medications. Taking quercetin along with these medications that are changed by the liver might increase the effects and side effects of your medication. Talk to your healthcare provider before taking quercetin if you take any medications that are changed by the liver.
Amitriptyline (Elavil), imipramine (Tofranil), metoprolol (Lopressor, Toprol XL), codeine, flecainide (Tambocor), haloperidol (Haldol), ondansetron (Zofran), paroxetine (Paxil), risperidone (Risperdal), tramadol (Ultram), venlafaxine (Effexor), and others are some medications that are changed by the liver.

Cytochrome P450 3A4 (CYP3A4) substrates interacts with Quercetin:

Some medications are changed and broken down by the liver. Quercetin might decrease how quickly the liver breaks down some medications. Taking quercetin along with these medications that are changed by the liver might increase the effects and side effects of your medication. Talk to your healthcare provider before taking quercetin if you take any medications that are changed by the liver.
Lovastatin (Mevacor), estrogens, indinavir (Crixivan), triazolam (Halcion), verapamil (Calan, Isoptin, Verelan), clarithromycin (Biaxin), cyclosporine (Neoral, Sandimmune), diltiazem (Cardizem), alfentanil (Alfenta), fentanyl (Sublimaze), losartan (Cozaar), omeprazole (Prilosec), lansoprazole (Prevacid), fluoxetine (Prozac), midazolam (Versed), ondansetron (Zofran), propranolol (Inderal), fexofenadine (Allegra), amitriptyline (Elavil), amiodarone (Cordarone), citalopram (Celexa), sertraline (Zoloft), ketoconazole (Nizoral), itraconazole (Sporanox), and numerous others are some medications that are changed by the liver.

P-glycoprotein Substrates interacts with Quercetin:

Some medications are moved by pumps in cells. Quercetin might make these pumps less active and increase how much of some medications get absorbed by the body. This might cause more side effects from some medications.
Diltiazem (Cardizem), saquinavir (Invirase), amprenavir (Agenerase), nelfinavir (Viracept), verapamil (Calan, Isoptin, Verelan), digoxin (Lanoxin) cyclosporine (Neoral, Sandimmune), loperamide (Imodium), quinidine, paclitaxel (Taxol), vincristine, etoposide (VP16, VePesid), cimetidine (Tagamet), ranitidine (Zantac), fexofenadine (Allegra), ketoconazole (Nizoral), itraconazole (Sporanox), and others are some medications that are moved by these pumps.

Dosing:

The appropriate dose of quercetin depends on several factors such as the user's age, health, and several other conditions. Typical dosages range from 500-1,000 mg per day. As quercetin has a low bioavailability, which means your body absorbs it poorly, the supplements may include other compounds, such as vitamin C or digestive enzymes like bromelain, as they may increase absorption.

Rheumatoid arthritis:

500 mg of quercetin can reduced early-morning stiffness, morning pain, and after-activity pain in women with rheumatoid arthritis.

High Blood Pressure:

Taking more than 500 mg of quercetin in supplement form daily reduced systolic and diastolic blood pressure by an average of 5.8 mm Hg and 2.6 mm Hg, respectively.  
However, always keep in mind that natural products are not always necessarily safe and accurate dosages are important. Make sure to follow relevant directions on product labels and consult your pharmacist or physician or other healthcare professional before using any product.


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